PSM 500
PSM 500
PSM 500
PSM-500/PSM-500L/500LT
Revision 0.91
Table of Contents
Appendices
Appendix A – PSM-500 Technical Specifications ............................................................... A–1
Appendix B – Remote Control Command Protocol ............................................................ B–1
Appendix C – Cabling Specifications .................................................................................. C–1
Appendix MUX – Framing/Multiplexer Addendum ......................................................... MUX–1
Appendix TPC – Turbo Product Codes FEC Addendum ............................................... TPC–1
Appendix HSSI – High Speed Serial Interface Addendum ........................................... HSSI–1
Appendix SNIP – SnIP Ethernet Interface Addendum .................................................. SNIP–1
Appendix LDPC – LDPC FEC Addendum ................................................................... LDPC–1
Note: All appendices may not be present in manual. Some Appendixes may be shipped with
the option.
Safety Notice
This equipment has been designed in accordance with UL and CSA standards for Safety of
Information Technology Equipment.
The PSM-500 Modem contains potentially lethal voltages inside the case. Extreme caution should
be exercised when the cover is removed by following the precautions listed below
Never operate the equipment with the cover removed. Never remove the cover with power applied.
As a safety measure the power cord should be disconnected from the unit when preparing to
remove the cover.
This modem is designed for indoor use. Do not operate this equipment in a wet environment or
outdoors.
Do not operate the modem in an unsafe environment near explosive or flammable gases or liquids
Insure good grounding practices. The grounding lug on the rear of the modem should be connected
to a good earth ground with low impedance cable in rack installations.
The modem is supplied with an IEC filtered power inlet module designed to accept a 3-wire mains
connection consisting of an earth ground, neutral and line conductors. The mating power cord
should have a line cord and plug suitable for the country of operation.
EMC Notice
This equipment has been designed in accordance with FCC and CE standards.
To maintain compliance with these standards the following the precautions must be observed.
The equipment must be operated with the cover and all cover screws in place.
Do not remove the rear panel option plate without replacing it with one designed for a specific option
assembly.
All rear connections are designed to have integral shielding on the cable and connector assembly.
“D” type signal connectors must have grounding fingers on the connector shell.
This manual is available in a printed form and as an electronic “Portable Document Format” or .PDF
file. The electronic format is produced as a universal Adobe Acrobat readable file, and can be
requested directly from Datum Systems, Inc., or via download from the web at
www.datumsystems.com. The electronic format on the web is always the latest revision.
Revision History
Revision 0.8 3/17/2006 Initial Public Release. ** Preliminary ** Requires minimum Modem
Software Revision 0.12.
Revision 0.83 12/4/2006 Still. ** Preliminary ** Includes additional FEC modes. Requires minimum
Modem Software Revision 0.21.
Revision 0.85 12/14/2006 Includes additional FEC modes and corrections. Requires minimum
Modem Software Revision 0.26.
Revision 0.86 8/12/2007 Includes additional FEC modes, corrections and new menu features for
Unit Configuration, RTS Monitor and Transmit Mute. Requires minimum
Modem Software Revision 0.52.
Revision 0.87 1/10/2008 Includes added Advanced TPC modes and corrections. Requires minimum
Modem Software Revision 0.63.
Revision 0.88 4/10/2008 Includes added 8QAM modulation, HSSI references, revised M500 Update
procedures and corrections. Requires minimum Modem Software Revision
0.72.
Revision 0.90 10/20/2010 Removes references to PSM-500H modem which is not available in the
PSM-500 Series.
Revision 0.91 7/15/2011 Update data rate limits and add more LDPC information. Added AUPC
setup example.
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The PSM-500 with a standard 70 (or 140) MHz IF is the first member of Datum Systems’ M500
Class Modem products, representing a major extension to our fifth generation of innovative design
concepts proven and refined over ten years of production. The PSM-500L is the second, utilizing L-
Band frequencies for both the Transmit and Receive IF, it creates the ability to build extremely
simple and low cost high performance VSATs All M500 class products encompass significant
performance improvement over previous modems at reduced cost. The PSM-500LT is the third,
providing an integrated BUC power supply.
The modem is designed for service in varied types of satellite systems. Either SCPC systems where
two modems are set for continuous operation with each other, or shared resource systems where
modem carriers are not continuous in nature, such as DAMA networks, where outgoing signals from
the modem can be operated in an extremely fast acquisition mode.
The modem is designed to be easily integrated into either a master or remote station via rack
mounting. A highly integrated design allows the PSM-500 to be built into a one rack unit (1 RU,
1.75”) high mounting case, using minimal power for dense applications. The modem is an integral
part of a satellite earth station’s equipment operating between the Data Terminal Equipment and the
station Up and Downconverter equipment.
1.0.1 How to Use This Manual
This manual provides Installation, Operating and Maintenance procedures for the PSM-500 Satellite
Modem and available options at the time of printing.
This manual is an integral part of the modem and is used to explain the installation and operating
procedures for the PSM-500 and present its capabilities and specifications. The manual is divided
into 4 Chapters with Appendices. The 4 Chapters are the Modem Description, Installation, Operation
and Maintenance. The Appendices include the Specifications, Remote Control Protocol and gives
further information on Options, Cabling and information related to placing the Modem in service.
The divisions of the manual are intended for use by personnel to answer questions in general areas.
Planners and potential purchasers may read the Introduction and Specifications to determine the
suitability of the modem to its intended use; Installers should read the Installation Chapter and the
Cabling Specification Appendix; Operating Personnel would use the Operations Chapter to become
familiar with the Modem; while System Programmers would use the Remote Control Protocol to
determine control requirements.
The PSM-500, 500L and 500LT modems are fully interchangeable with the single exception of the IF
input frequency range. In addition all options available for the PSM-500 are usable with the L or LT
version. The term PSM-500 is used throughout this manual where references apply to either the
PSM-500, 500L or 500LT modems. Where a subject is specific to one modem the “L” or “LT” suffix is
used or the specific differences in operation between the three modem versions are detailed.
1.0.2 Quick Start for Experienced Modem Users
If you are experienced with modems, but not this particular one, you may want to skip some of the
introductory material and learn how to operate the front panel to set up the modem immediately. Go
directly to Section 3.1 – “Operating Procedures” and get a feel for how the front panel operates.
Then scan Tables 3-1 through 3-4 listing the parameters that can be changed, and set up the
modem for your application. We strongly recommend that you go back to learn more, as these
modems have extensive capabilities and features that are unique. A list of abbreviations is located at
the end of the “Frequently Asked Questions” (FAQ) in Chapter 4.
1.0.3 What’s New – This Modem and This Manual
If you are familiar with Datum Systems modems, especially the PSM-4900, then you should feel
comfortable with both this modem’s operation and this manual. There are some significant
differences you should review in the list below.
New in This Modem:
• The PSM-500 series is the first to include 8PSK, 8QAM and 16QAM modulation modes,
requiring new procedures and remote control interaction.
• The PSM-500 now includes remote control and firmware update via USB interface on the
rear panel. This was especially necessary since the 10 fold increase in firmware requires a
faster method to load new firmware configurations.
• Each PSM-500 IF version is capable of 3 standard value software upgradeable “Feature
Sets”, as described in section 1.1.2. Many features of the modem are field upgradeable
without adding new hardware. Subsets of these Feature Sets are available.
• There are two option slots on the main PCB used for FEC/processing options. One is
always used for the standard FEC set as a minimum. They are wired in parallel like the PCI
slots on a computer, but use an SO-DIMM form factor. Please don’t plug memory in!
• The IBS multiplexer with AUPC is now standard and built into the main board FPGA logic.
• The Reed-Solomon concatenated FEC is now standard and built into the standard FEC
card.
New in This Manual:
• A new “How-To” Appendix is added in Appendix H. It gives quick instructions on setting up
common features and capabilities.
Max Data Rate M523 rates slightly higher at higher FEC rates. See Notes below.
BPSK 2.46 Mbps 2.5 Mbps 5 Mbps 7.38 Mbps
QPSK/OQPSK 4.92 Mbps 5 Mbps 10 Mbps 14.76/28 Mbps
8PSK/QAM/TCM N/A N/A 10 Mbps 29.52 Mbps
16QAM/APSK N/A N/A N/A 29.52 Mbps
FEC Modes
Disabled N/A � � �
Viterbi � � �
Reed-Solomon Option � � �
TPC – 4K (2) Option Option Option Option
TPC – 16K N/A Option Option Option
LDPC-16k (2k) N/A Option Option Option
There are multiple items lists as “Options”. Options are specifically hardware items that are installed
in the modem, while a “feature” is a software installation listed as an “upgrade”. To upgrade the
modem from one feature set to another refer to the instructions in Section 4.4.
Maximum data rates are dependent on many factors besides the basic capabilities of the interface,
including cabling, interface type, features and options installed. The TPC4K hardware codec is
limited to 5Mbps.
1.1.3 Applications
Following are just a few representative forms of satellite communications links and networks in
which the PSM-500 modem series may be used.
1.1.3.1 SCPC Point-to-Point Links
The most straightforward application for a satellite modem is to serve as the Data Communications
Equipment (DCE) for a point-to-point data link. When used in this mode, two modems located at two
different sites are tuned to complementary transmit and receive frequencies. Each direction of the
communications link may have the same or entirely different transmission parameters. In this
application it is typical that the link is established and maintained on a continuous basis, although a
special “on demand” case is described later.
In SCPC point-to-point links the power required from the satellite or the size of the receive antenna
is dependent upon the modem receive performance. The PSM-500 modem uses the most rigorous
methods to maintain performance as close to the theoretical “waterfall” curves as possible. In most
cases the modem will perform at 0.1 to 0.2 dB from the curve (although we say “typically” 0.3 dB).
This consistent performance, plus advanced technology such as TPC results in the absolute
minimum power requirements, which equates to the minimum operating.
Ku Band satellite systems are subject to changing performance due to rain at one or more sites. The
PSM-500 contains built in software to perform Automatic Uplink Power Control (AUPC). If the
modems at each link end are provided with an external asynchronous channel of 300 bps they can
be set to automatically maintain a constant Eb/No within programmable limits. This can result in
significantly lower satellite power requirements in a large system in addition to maintaining proper
performance in any system. The optional Multiplexer/interface card can provide this low rate channel
in addition to an Earth Station to Earth Station overhead service channel.
1.1.3.2 SCPC Point to Multi–Point Links in a Broadcast Application
A broadcast application might involve the necessity of sending continuous or intermittent data from
one source and
“broadcasting” the
information to many
remote locations. For
instance, constant Satellite
pricing information and
updates may be sent by
a central location to
many store locations.
Remote C
There may be minor Remote A
return information from
the remotes
acknowledging receipt.
Another broadcast
application could be
Remote D
transmitting background
music from a central
location to many store Remote B
Hub Station
sites. In this case there
would be no return path. Figure 1-1 Simple Star Network
The topology of the
network in both of these broadcast examples would typically be called a “Star” network. As shown in
Figure 1-1, the shape of the configuration is drawn with the central “Hub” as the center of the star
and the remotes as points of the star. In both cases the transmit frequency and other parameters
may be shared by the receive of all the remotes.
The PSM-500L and LT are ideally suited for use at remote or small stations. Since the receive down-
converter requirement is significantly reduced in this version, requiring only that a data grade LNB
(Low Noise Block down-converter) be connected to the modem. The L-Band version modems can
even supply power and reference to the LNB if needed. In addition the PSM-500L and PSM-500LT
modems are designed for use with a Block Up Converter or “BUC” and can supply power and
reference signals on the transmit cable. Most BUCs today are designed to receive these signals on
the cable.
In Broadcast type systems where the remotes only require a receiver, the L or LT is very low cost
and the transmit modulator section can be simply turned off.
A “Star” network configuration is also commonly used with multiple point-to-point links where the hub
is common to every link. An example might be where each remote represents a house or building
with voice or data traffic all destined for a common switch located near the hub. Each link is then
usually dedicated to that customer and the link resources are wasted when no traffic is carried. That
loss is partially offset by being able to use smaller antennas and power at each of the remotes,
concentrating costs at the hub.
1.1.3.3 DAMA (Demand Assigned Multiple Access)
Suppose that we wanted to simulate a telephone network with a virtual switch between modems
carrying digitized voice information. We might use a central computer to assign a pair of frequencies
for any conversation and send this connection information to the proper sites to set up the
connection. Many systems of this type use “Star” network topology, but this has the disadvantage
that for a person at Remote A to talk to someone at Remote D the traffic must go through the hub.
The resulting delay through 2 satellite hops is just at the limit of what is tolerable for voice traffic.
In this application a new network configuration is usable. That is a “Mesh” network where any of the
voice modems at any site can be programmed to link with any other modem directly at any other
site. The resulting link diagram looks like a mesh of interconnects. Now there must be sufficient
antenna size and power at each remote to link to every other remote. The station costs can go up
significantly, and are multiplied by the number of stations.
Since the frequencies can be assigned on demand, the network is then called “Demand Assigned,
Multiple Access”, or DAMA. One important characteristic of a DAMA system used for voice
information is the lock-up time of the modem. At the low data rates used to digitize voice today (4.4
to 32 kbps) the modem receive acquisition method of sweeping results in lock-up times of tens of
seconds to minutes. The PSM-500 modem is uniquely designed to significantly reduce this time:
The fast acquisition digital signal processor used in the PSM-500 looks at the receive signals within
its acquisition range much like a person might view the same region using a spectrum analyzer. It
then “homes in” and locks to the most probable carrier. This acquisition mode can reduce the
rd
receive acquisition time to approximately 1/3 of a second at 9.6 kbps in QPSK mode over +/- 30
kHz, and less in BPSK mode.
1.1.3.4 TDMA (Time Division Multiple Access) Remote Site Application
In a TDMA network the central Hub continually transmits a stream of outbound data containing
information for multiple remote sites, while the remotes transmit back to the Hub on a timed basis.
Each of these remotes is said to “burst” its information back on a specific frequency. This may be the
same inbound frequency for all sites. Each of the remotes is responsible for accessing its own
information from the outbound data stream by reading the address assigned to specific parts of the
data.
The TDMA network usually looks like the Star network described above. The outbound (from the
Hub) data rate may be quite high to accommodate many remotes with low latency, while the inbound
data rate may be low to allow use of a small antenna and power amplifier at the many remote sites.
The PSM-500L is specifically designed to be usable as the remote site modem of a TDMA network
when coupled with a proper “Burst” demodulator at the hub site. Note: As of the time of this
manual the “TDMA burst” mode is a special factory request option and not installed in
standard modems.
Another variation could use both the DAMA (star or mesh configuration) with a concurrent TDMA
system as the monitor/control network for the DAMA. Again the PSM-500 modem is ideally suited for
both modem applications at both low and high speeds.
RTS RS-449 P1
or
Figure 1-2
Attenuator
Ext. Reference In
Interface & Loop- MODULATOR Modem
Back Circuits Reference
DEMODULATOR Oscillator
Term
RCV In
70 MHz
RData Program DSP Aquisition (or L-Band)
Receive Synthesizer
mable Processor
Receive Doppler
Interface FIFO Buffer
Ext
RS-449 Clock
FIFO P1
or Control
Clk
V.35
or V.35/Intelsat
Ready RS-232 and FEC Baseband Signal A/D Front end
Demodulator
etc. Differential Decoder Processing Conversion AGC/Amp
Decoder
Page 1-7
Figure - M500 Modem Block Diagram
Description
Description PSM-500/500L/500LT SCPC Satellite Modem
1.2.1 Modulator
The PSK/QAM modulator in the modem employs a unique digital modulation scheme requiring no
heterodyne operations (mixing and filtering to an IF) to arrive at the transmit RF frequency. The
desired carrier frequency is synthesized and directly modulated with the baseband signal. The
baseband signal is itself digitally derived and generated using a digital to analog (D/A) converter.
The digital signal processing of the transmit signal includes the equivalent of a 144 tap FIR filter
function.
As previously shown in Figure 1-2, synchronous transmit data and clock signals are accepted by the
modulator, then processed by the V.35/Intelsat scrambler and differential encoder. The modulator
can be set by the processor to operate at a number of data rates between 1.2 kbps (BPSK, rate 1/2)
and 20 Mbps (8PSK +, M520 feature set). Refer to the specification in Appendix A for exact rate
capabilities. The data is then encoded for Forward Error Correction (FEC) at rate 1/2, 3/4, 5/6 or 7/8
resulting in an encoded signal at between 2.4 and 14,760 ksps (kilo symbols per second). The
Viterbi convolutional encoder can be programmed for rate 1/2, 3/4, 5/6 or 7/8 and is set for a
constraint factor (K) of 7 for use by a (receiving end) Viterbi convolutional decoder with the same
rate and K factor. A Reed-Solomon FEC is available for concatenated operation with the Viterbi
Codec and two types of “Turbo Codes” Codecs are also available to replace the Viterbi Codec. A
special case is 8PSK, which only operates in a Trellis Code Modulation (TCM) mode at rate 2/3,
unless a non-Viterbi FEC is added such as TPC or FlexLDPC.
The FEC is followed by an optional differential encoder. The differential encoder output is then sent
to the transmit baseband signal processor whose main function is to convert the data stream into
analog baseband I and Q channels for modulating the carrier. The actual conversion process is
accomplished in a lookup table, latch and D/A converter. The lookup table represents a digitally
preprocessed function required to produce the proper RF signal output when mixed with the desired
carrier frequency. A low-pass filter is applied to the D/A output to reduce the level of sampling
components.
Transmit Local Oscillator generation is accomplished in two parts. A PLL step synthesizer is used to
generate a basic LO in the 52 to 92 (or 104 to 184 or 952 to 1752) MHz range with 500 kHz step
size. A Direct Digital Synthesizer (DDS), consisting of an NCO and D/A conversion, is used to
generate an approximate 2 MHz signal with fine step size of approximately 1 Hz and a range of
±1.25 MHz. When the DDS is subtracted from the step synthesizer output in a second PLL, the
available LO can be tuned in 1 Hz steps over the full range of 50 to 90 MHz (100 to 180 MHz if built
for that version).
The processed baseband signal is then mixed with the transmit synthesizer's LO carrier signal to
generate an output modulated carrier in the 50 to 90 MHz range (or 950 to 1750 MHz in the L-Band
modem). A classic IQ modulator with two mixers is used and the LO is fed into the second mixer
shifted 90 degrees from the first. The modulated baseband signal can take two forms at this point
depending on whether BPSK or QPSK modulation is used. In BPSK mode, the baseband signal fed
to the two mixers is identical. In QPSK mode, the two signals represent the baseband I and Q
channels of the baseband.
The resultant RF signal is then low pass filtered and amplified to produce a signal at approximately
over 5 dBm into 75Ω. An output attenuator controlled by the onboard processor is used to set the
modulator output level over a range of +5 to –35 dBm. The actual attenuator is a set of pin diodes
whose voltage is derived from the processor via a 12-bit D/A converter. The processor also holds a
calibration table of DAC input vs. RF output level/frequency in non-volatile memory.
No physical adjustments are present in the modulator. All necessary adjustments are electronically
performed during calibration and are intended to last the life of the unit without requiring resetting.
The modulator is capable of operating in two different modes: Continuous mode for SCPC use and
“Burst” mode for use at a VSAT location. When set to VSAT operating mode, the transmit signal is
turned off and on according to the status of the data interface control lines and framing information in
the data stream as described in the “Operation” Chapter of this document. The burst mode allows
multiple station modulators to link up consecutively with a single master station “burst demodulator”.
Note: As of the time of this manual the burst mode is a special factory request option and not
installed in standard modems.
The Modulator IF output can be routed to the Demodulator input using a built-in “IF Loop-back”
function. The loop-back path provides a 25 dB attenuator to avoid overloading the receive input.
1.2.2 Demodulator
The Modem Demodulator uses direct conversion techniques for recovery of data from an incoming
carrier, and therefore like the modulator does not use heterodyning, and has no internal IF signal or
processing. Referring to Figure 1-2, the input RF signal is first input to the receive AGC amplifier.
The AGC amplifier has a range of greater than 40 dB at any data rate, allowing inputs over that
range while still meeting performance criteria. The range is controlled in several steps depending on
the data rate extending over the range of –20 dBm at high data rates to –84 dBm at low data rates.
The proper AGC gain is digitally determined as that which produces an optimal output from the A/D
converters and is thus derived after the A/D converters.
The RF input is then demodulated using a “Costas Loop”, phase locked loop demodulator where the
signal is split using a 90 degree hybrid into I and Q channels. In BPSK mode, the I channel carries
the data information and the Q channel represents the noise and carrier phase information in the
Costas loop. For QPSK operation, the I and Q channels each carry data information. The I and Q
channel “eye” signals are not available as in many other modems because the signal/data
representation at this point is still strictly digital for direct signal processing.
A receive synthesizer generates the demodulator local oscillator which is at the desired receive
carrier frequency. The synthesizer is tunable over the range of 50 to 90 MHz (or 950 to 1900 MHz in
the L-Band modems) and has two tuning components; the LO step synthesizer used to tune in steps
of 500 kHz, and a Direct Digital Synthesizer (DDS) component used to acquire and track the
received carrier. The DDS control has two tuning sources; (1) the digital Costas demodulation loop
phase detector used to track an already “locked” signal and (2) the processor control used to set the
carrier frequency and acquire new signals. The processor controls the acquisition search over a
programmable range from ±100 Hz to ±1.25 MHz.
The I and Q channel baseband outputs of the Costas Loop demodulator are converted to digital data
streams by parallel 12 bit D/A converters. The digital information is then filtered via a Datum
Systems’ proprietary programmable digital filter. The filtered sample output is sent to the input of the
Forward Error Correction (FEC) process (either Viterbi convolutional, concatenated Reed-Solomon,
8PSK TCM rate 2/3, Turbo Codes or LDPC decoder) circuit. Multiple bits of the filtered A/D
converter are used for “soft decision” decoding in the FEC, providing an improvement in
performance over hard decision decoding.
The A/D output is also available to a special Digital Signal Processor (DSP), which is used to
examine the incoming signals for known energy patterns and acquire carriers significantly faster
than conventional sweep acquisition. This DSP controlled acquisition is especially useful at low data
rates and can improve over a typical sweep by more than 2 orders of magnitude.
The receive signal processing shown in Figure 1-2 serves the following multiple functions:
1. Generates the soft decision symbol information for input to the FEC.
2. Recovers the bit rate clock from the incoming signal.
3. Measures the Es/No of the received signal.
4. Generates the receive AGC signal to set the input stage gain.
The FEC decoders are contained on one or two adaptor cards plugged into the main board (all
except the TPC are contained with the adaptors FPGA), which is under control of the onboard
processor.
A differential decoder and INTELSAT / V.35 descrambler for the received data signal can be
individually enabled or disabled by the processor based on the current FEC and other settings. It is
no longer under control of the front panel or command interface. This configuration is held in the
nonvolatile EEPROM and does not have to be reconfigured on power-up. The resulting received
data and clock signals are sent to the interface assembly. Receive interface clocking can take
several forms as explained below.
Send Data
From DATA
Interface
Send
Timing To CLOCK
Interface
Modulator
Terminal Terminal
Timing Timing
From
Interface
From
Receive
Clock
Receive
Data To DATA OUT IN DATA
Interface
Receive FIFO
Demodulator
Buffer
Receive CLOCK
Timing To OUT IN
Interface
External
FIFO Clock Demodulator RCV Demod output
From CLOCK clock is phase
Interface locked to receive
From Modulator
bit timing bit timing
These Clock sources may be used in various ways in a system implementation to provide correct
timing at a destination. Each of the clock sources can be set either from the front panel or from an
external monitor and control system.
The un-terminated versions of these standard interfaces and are used to implement one for one
(1:1) redundancy between two PSM-500 units.
A single 37 pin “D” type female connector is available on the rear panel at J3 providing the terrestrial
data interface. The interface standard is electronically selectable via front panel or remote control.
Optional interfaces are provided by a separate option interface card which is mounted inside the
modem chassis. The provision of an optional interface “adds” to the available interfaces which can
be selected under program control. An interface field kit of parts to add an option interface is
available from the manufacturer for installation by qualified technical field service personnel. When
an optional interface is installed the main processor automatically queries and installs the necessary
software controls for accessing the interface.
When the modem is placed into either the “Enhanced” or “Custom” modes the AUPC control
channel becomes available. The AUPC operation itself is under control of the modem while the
AUPC facility in the MCC provides the channel for the information. This channel provides a minimum
300 baud control channel in each direction to allow the modems at two ends of a link to interactively
maintain the receive Eb/No by controlling the power output at the transmit site.
Refer also to the AUPC operation description of the main manual in Section 3.8 titled “Automatic
Uplink Power Control (AUPC)” Operation.
1.2.7.1.2 Remote Modem Control Channel (RMC)
When the modem is placed in the “Custom” mode the Remote Modem Control Channel becomes
available. This channel allows the control of a far end modem from the near end site. This control is
not however allowed from the near end front panel, but only via the remote control interface port.
The command protocol for remote unit control is explained in Appendix B, “Remote Control
Protocol”.
Note that the Automatic Configuration Recovery or ACR is partially designed as a safety feature to
be used with the remote programming of modems. It can help prevent “losing” the modem at an
unattended site. Refer to the ACR section of the main manual in 3.14 “Automatic Configuration
Recovery”.
1.2.7.1.3 Auxiliary Bit Control Channels (RFC)
When the Multiplexer is placed into the “Custom” mode the auxiliary bit control RFC channels
becomes available. These consist of two single line or “one-bit” control channels that can be used to
send control information independently in both directions over the link. The input signals on these
channels can be either a contact closure or a logic type signals while the output is a form C relay
contract set whose state depends on the state of the input signal. The low input logic level is 0 to 0.4
VDC, while the logic high level can be from 2.4 to approximately 20 VDC. The input is current limited
to accept this wide voltage range without damage. Higher voltages may damage the inputs however
and caution should be exercised. Pin connections for these one bit channels are shown in the RS
Appendix.
error correction. For example, the common rate ½ means that for every data bit two bits are
transmitted, and in rate 5/6, 6 bits are transmitted for every 5 data bits. Better performance is
commonly considered higher coding gain at a given rate. There are always other factors to consider,
such as the latency (processing time) required, time to recover from a synch loss, signal acquisition
time, etc, etc.
FECs technology is often specifically adapted to a particular use. For example, it is common to use
special forms of Reed-Solomon, TPC and LDPC for video signals. These type signals and FECs
typically have a fairly high performance floor that are of little consequence for a wideband video
signal, but would be entirely unacceptable for most data information especially at low data rates.
Viterbi has been the standard high performance FEC used in satellite communications for
approximately 10 years. It has only been in the past few years that new technologies have emerged
which provide more coding gain with reasonable implementations. The standard PSM-500 FEC card
includes the circuitry for a Viterbi, TCM and Reed-Solomon Codec providing the PSM-500 with basic
functional capability for all standard operating parameters including 8PSK TCM and 16QAM. The
following are general descriptions of the characteristics of each of these functions.
The table below shows the currently available modes depending on modulation.
Note in Table A that the front panel selection number for each of the options is listed as the “Sel #”.
For example The Modulation modes show the selection numbers 0 through 6, and the FEC Type,
Option and Code Rate selection numbers are listed in the column to the right of each item. These
numbers can be referred to for front panel operation but are even more applicable to the SnIP Telnet
command line program named “m500ctl”. This program has specific commands that allow entering
either just the 3 digit FEC options or the full Modulation, FEC Type, Option, Code rate and Reed-
Solomon mode (MTOCR) in a single entry. Refer to the SnIP documentation for more information.
1. The TPC M5 Full, Short and Legacy modes are intended for PSM-4900 Compatibility only
2. * TPC 4k/16k restrictions apply to that line and Code Rate only
3. TPC4k Max data rate limits see below
4. TPC16k operates up to 20 Mbps depending on Feature Set and modulation
5. The Viterbi, Rate 3/4 & 7/8, 16QAM CT modes are only for Comtech modem compatibility as
they only operate in this mode with R-S at 220, 200, depth of 4. R-S is auto-enabled
6. TPC Advanced modes are Datum Systems proprietary implementations that require the
TPC16k option only for the colored lines. They offer superior performance to CT modes
Transmit
Transmit Data Channel
Terrestrial Data
Channel Transmit Reed-Solomon
Transmit Reed-Solomon
Block Encoder &
Block Interleaver
Synchronous Scrambler
Control
Clock
XMT
IBS
Clock and Frame Main Modem
Multiplex Processor Clocks
Generation Assembly
Option
RCV
Control
Clock
Receive
Terrestrial Data Receive Data
Channel Channel
Receive Reed-Solomon
FIFO From Block Decoder & Receive Reed-Solomon
Main Modem Synchronous Block De-Interleaver
Descrambler
The Reed-Solomon modes shown available below can be selected from the front panel or remote
control. The CT220,200 mode is a special compatibility mode and is automatically set by certain CT
FEC modes, for example when Viterbi, Rate ¾ is selected when in 16QAM mode. It can be over-
ridden by choice from the Reed-Solomon parameter.
Chapter 2 - Installation
2.0 Installation Requirements
The PSM-500 VSAT/SCPC Modem is designed for installation in any standard 19-inch
equipment cabinet or rack, and requires 1 RU mounting space (1.75 inches) vertically and 12
inches of depth. Including cabling, a minimum of 15-inches of rack depth is required. The rear
panel of the PSM-500 is designed to have power enter from the left and IF cabling enter from the
right when viewed from the rear. Data and control cabling can enter from either side although
they are closer to the left. The unit may be placed on a table or suitable surface as required.
2.1 Unpacking
The PSM-500 Modem was carefully packed to avoid damage and should arrive complete with the
following items for proper installation:
1. PSM-500 Modem Unit. L-Band Units may include an external BUC power supply.
2. Power Cord, 6 foot with applicable AC connector.
3. Installation and Operation Manual plus other information on CD.
2.1.1 Removal and Assembly
If using a knife or cutting blade to open the carton, exercise caution to ensure that the blade does
not extend into the carton, but only cuts the tape holding the carton closed. Carefully unpack the
unit and ensure that all of the above items are in the carton. If the Prime AC power available at
the installation site requires a different power cord/AC connector, then arrangements to receive
the proper device will be necessary before proceeding with the installation.
The PSM-500 Modem unit is shipped fully assembled and does not require removal of the covers
for any purpose in normal installation. All normal hardware configuration, including setting the
data interface type and IF impedance is under software control. The type of Feature Sets, FEC
Options and Interface Options installed can be read from the LCD display on the front panel
under <Unit: Status – > column by scrolling down after initial application of power.
Should the power cable AC connector be of the wrong type for the installation, either the cable or
the power connector end should be replaced. The power supply itself is designed for world-wide
application using from 90 to 264 VAC (100 to 240 VAC +/- 10%).
providing a 1 RU space for airflow. Modem units should not be placed immediately above a high
heat or EMF generator to ensure the output signal integrity and proper receive operation.
Do not mount the PSM-500 in an unprotected outdoor location where there is direct contact with
rain, snow, wind or sun. The modem is designed for indoor applications only.
The only tools required for rack mounting the PSM-500 is a set of four rack mounting screws and
an appropriate screwdriver. Rack mount brackets are an integral part of the front panel plate of
the unit and are not removable.
The following interface connections should be available at the mounting location as a minimum:
1. Prime AC power.
2. A 75Ω Transmit IF cable with BNC male connector. (50Ω optional) or a 50Ω Transmit
IF cable with type N male connector for the L-Band version.
3. A 75Ω Receive IF cable with BNC male connector. (50Ω optional)
or a 75Ω Receive IF cable with type F male connector for the L-Band versions.
4. A Terrestrial data interface cable to mate with the modem or installed option; either a
37-pin male “D” sub connector for all standard or appropriate connector for an
optional interface (such as G.703 or Ethernet 10 Base T).
Other optional connections are shown below.
The ESC channel connection at 37-pin male “D” sub connector J4 (AUX). (When the optional
IBS multiplexer is enabled). See Appendix C, “Cabling Specifications” for the pins used
for each of the following interfaces available on the “AUX” connector.
J1
J10 MADE IN U.S.A.
90 - 260 VAC, 50 W.
J8 XMT IF OUT
AC AUX J5
S1
Line J4 EXT. REF IN
Alarm BUC PWR IN BUC PWR RCV IF IN
J7 Status J9
Control J6 J11
J3 Data Interface
L-Band IF Modem
Page 2-5
Installation
Installation PSM-500/500L/500LT SCPC Satellite Modem
1 Shield (GND) Shield (GND) Shield (GND) SHD (GND) GND (4)
4 Transmit Data (A) – SD A (SD-) SD TD A Input
21 External data Clock Ext Data/FIFO Clock Ext Data/FIFO Clock Ext Data/FIFO Clock Input
(transmit data clock or B (+)*(3) B (+)*(3) B (+)*(3)
receive FIFO Buffer
output Clock (B) + *(3)
10 Mod Fault Alarm *(2) Mod Fault Alarm *(2) Mod Fault Alarm *(2) Mod Fault Alarm *(2) OC TTL
output
28 Demod Fault Alarm Demod Fault Alarm Demod Fault Alarm Demod Fault Alarm OC TTL
*(2) *(2) *(2) *(2) output
32 Aux RS-232 Receive Aux RS-232 Receive Aux RS-232 Receive Aux RS-232 Receive Input
*(1) *(1) *(1) *(1)
34 Aux RS-232 Transmit Aux RS-232 Transmit Aux RS-232 Transmit Aux RS-232 Transmit Output
*(1) *(1) *(1) *(1)
The USB type B connection is also available for use as a remote control connection, although its
primary purpose is loading new firmware. Computers that do not have an available RS-232 port
could use of this port for control, but it requires that a special USB device driver be loaded into
the computer to access the modem via this port. This driver makes the control port appear similar
to a serial port. The latest driver is available on our web site.
Table 2–2.
Remote Control Connector J6 Pin Assignment
Refer to Appendix C, “Cabling Specifications” for information on making a remote control cable.
2.3.3 Alarm Connection
The modem has two form-C dry contact alarm relays on board and an alarm connector located
on the rear panel, the 9-pin male “D” sub connector J5.
The two relays are designated “A” and “B” and the particular alarms that are summarized on each
relay are programmable from the front panel of the unit or via remote control. Connection to the A
and B relays is via the proper set of pins as shown in Table 2-5 below and programming the
applicable alarm entries via the front panel control or remote control. Non-Alarm is defined as the
powered state of the relay resulting in an alarm when power is lost.
The analog monitor output is programmable from the front panel to select either receive Eb/No,
receive AGC voltage or transmit output power.
Table 2–3.
Alarm Connector J5 Pin Assignment
J5 Pin # Connection
1 Relay A - NO on Alarm Note:
2 Relay A - Common By convention “NO”
3 Relay A - NC on Alarm means Normally Open,
and “NC” means Normally
4 No Connection Closed.
5 Analog Monitor Output (1kOhm) Both conditions are the
non-powered, Alarm State.
6 GND for analog monitor
7 Relay B - NO on Alarm
8 Relay B - Common
9 Relay B - NC on Alarm
Note: The two modems should be at the same firmware revision for proper redundant operation.
The two modems operate in a “non-priority” redundancy mode, that is, no modem is specified as
“primary”, or having preference when both modems are operational. The first modem turned on
assumes a non-redundancy mode until the second connected unit is powered up. The on-line
unit can be set to send its configuration information to a second unit via the front panel. The
modems will remain in this state, constantly sending status information back and forth until one
unit indicates a failure. If that modem is currently on line, it is switched off-line and the alternate
unit is switch on.
The modem is also capable of operating in 1:N and M:N redundancy switching schemes. The
necessary connections to monitor and control switching are available on the data connector itself
in the form of the modulator and demodulator fault outputs and the auxiliary RS-232 control port.
The alarm outputs are also available. The other facility provided to aid in these redundancy
schemes is the ability to save and recall configuration information. Thus a back-up modem can
obtain and save the configurations from 8 other modems and switch immediately to the
necessary parameters to replace any of those units by simply recalling that unit’s stored
configuration. In addition, the programmable interface and common physical data connector
allows different interface protocols between the primary modems.
A diagram of the connections required for installing 1:1 redundancy is shown in the figure below.
Station IF
Data "Y" Cable Paired Modems
Equipment
Xmt IF
Transmit
Modem A IF
Combiner
Aux Xmt
Rcv IF
Aux Rcv
Aux Xmt
Receive IF
Modem B
Splitter
Rcv IF
It is important in L-Band systems to use special splitters and combiners that have the ability to
pass DC used to power the BUC and LNB with sufficient current capacity. One type of these is
termed “Wilkinson” combiners. For the lower power receive LNB connection there are low cost
DC pass combiners that may be suitable. Visit our web site for recommendations.
⇒ CAUTION: Before initial power-up of the modem, it is a good idea to disconnect the
transmit output from the operating satellite ground station equipment. This is especially
true if the current modem configuration settings are unknown, where incorrect setting
could disrupt existing communications traffic. New modems from the factory are normally
shipped in a default configuration which includes setting the transmit carrier off.
Turn the unit “ON” by placing the rear panel switch (above the power entry connector) to the “ON”
position. At every power-up, the modem processor tests itself and several of its components
before beginning its main monitor/control program. These power-up diagnostics take
approximately 1 second and show no results if successful. If a failure is detected, the indications
vary by the type of fault detected. A serious failure will result in the front panel Alarm LEDs
flashing at a rate of approximately 4 times a second, and the unit beeper sounding.
Most potential failures will result in the modem giving a verbal indication of the problem on the
front panel LCD display. Status indications are shown highest priority first.
The initial field checkout of the modem can be accomplished from the front panel or in the
Terminal Mode. The Terminal Mode has the advantage of providing full screen access to all of
the modem’s parameters, but requires a separate VT100 terminal or computer running a terminal
program in VT100 or ANSI mode. The modem unit is placed into terminal mode by setting two
options via the front panel. First set the <Unit: Remote – Protocol> parameter to “VT100”
(option 0), then set the <Unit: Remote – Port> parameter to “RS–232” (option 0). The <Unit:
Remote – Bit Rate> and Format also require setting to match the terminal settings. The <Unit:
Remote – Address> serves no function in the Terminal mode. See below for a quick introduction
on the use of the front panel and steps for entering parameters.
and down arrow keys to arrive at the “Level” parameter. This is shown by convention in this
manual as <Mod: IF – Level>
“2047” pattern or “2” for a “2^23-1” pattern. The “0” key will disable the BER test mode. BERT test
readings are displayed in the <Int’f: Status - BER> parameter and the 6 items below it.
Since there is no noise added in the IF Loop-back mode the BER results should show no errors.
This test is more useful once the modem is configured and a Loop-back over the satellite is
performed by setting the receive frequency to that output by the modulator.
The IF Loop-back state and the BERT state are both stored in EEPROM, therefore if the unit is
powered off during IF loop-back and/or BERT test it will return to this state when powered up
again.
More information on the BERT functions is given in Section 4.1.2 “Using the Built-in BERT”.
2. The L-Band modems with L-Band Receive can be set to supply power at either 13 or
18 VDC and/or a 10 MHz reference signal on the receive input connector for coupling
to the LNB via the receive cable.
enable this feature simply supply the <Mod: BUC – LO Frequency> parameter with a value
other than “0”. When the value set here is equal to the BUC’s LO frequency then the modem can
automatically compute the RF frequency at the BUC output.
The PSM-500L modem will also determine if the LO is high or low side and sets the spectrum so
that it is always “Normal”, i.e. not inverted. You do not have to change the IF spectrum setting
from “Normal” to achieve this.
Note: After entering a new BUC LO frequency the modem requires a new Transmit IF
frequency input to recalculate the proper output frequency setting.
To return to using the L-Band IF frequency setting, simply enter a value of “0” into the BUC LO
parameter. A common BUC LO frequency for the C-Band 5.925 to 6.425 GHz Range is 4900
MHz (low side LO), while a low side LO for the Ku Band 14.0 to 14.5 GHz range is 13150 MHz.
The hybrid “Auto Narrow” and “Auto Track” modes available in previous generations of this
modem are no longer available as separate entries. The “Auto Narrow” function of initially
searching in a smaller acquisition range is incorporated into the latest version of the “Search”
mode. Setting the “Search” mode also enables a new menu item for “Sweep Time”. To be
enabled the <Dem: IF – Sweep Time> is set to a value other than 0 Seconds. Then, when a
carrier lock is lost, the modem will search in a reduced acquisition range (equal to the symbol
rate in Hertz) for the specified Sweep Time.
The “Search” acquisition mode also allows a modified version of the previous “Auto Track”
function. When in this mode the modem can be commanded to an offset from the set receive IF
frequency and the modem will begin its narrow search about that offset for the specified Sweep
Time. In this mode the Demod Offset may be set by any command method and the demodulator
will search at that point in the narrow DSP mode. (Note that in the standard fast acquisition mode
the Demod Offset is read only) This mode is intended for possible DAMA use where the offset
can be maintained to insure the fastest lock time.
The acquisition mode is set by setting the <Demod: IF - Sweep Mode> option parameter to
either “Fast” (0), or “Search” (1). The “Fast” mode is the standard setting.
Once all parameters have been set and verified, the transmit output can be connected to the
ground station equipment for transmission to the satellite. Verify that the alarms are extinguished
and that the demodulator has locked.
The PSM-500 Alarm system represents a sophisticated method of controlling visual, relay and
logical alarm outputs which can be used for multiple purposes including redundancy. A basic
representation of the alarm system functioning is shown in the figure below.
Summary Alarm
Unit Alarms
Reference
Test Active
NC
Hardware Alarm Relay A
NO
C
Modulator Alarms
NC
Carrier Alarm Relay B
NO
Bit Clock C
Test Active
Hardware
No Data
Selection
Demodulator Alarms Modulator Front Panel
Logic
Carrier Lock Alarm
Low Level Data
Low Eb/No Interface
Test Active
Hardware
No Data
Redundancy
Switch Request
There are also other possible alarm inputs depending on the modem options and configuration.
Each of the individual alarm inputs has a configuration selection parameter under the “Alarm”
column of its matrix. The general options available are to set the alarm to either be ignored or to
form one of the “OR” inputs to the A or B alarm relay or both. The default set-up for these alarms
is to have all the modulator related alarms assigned to Alarm A and all demodulator alarms
assigned to Alarm B. The two alarm relays could be changed to represent “Major” and “Minor”
alarms.
The open collector outputs for the modulator and demodulator alarms are available on the data
interface connector and are used by some types of redundancy switches for determining alarm
status. The modem’s built-in redundancy switch logic uses either all alarms or combinations of
the A and B alarms to activate a switch request.
A description of each of these settings is contained in Operations, Section 3.2 and Tables 3-5
through 3-8 later in this manual. A brief description of alarm configuration is also given here.
Possible alarm sources include the following items:
1. Unit Reference missing.
2. Unit Test Active.
3. Unit Hardware Fault.
4. Transmit Carrier Off.
5. Modulator Bit Rate Lock.
Manual tuning of the modem’s reference is accomplished using the <Unit: Ref – Fine Tune>
parameter and entering a value from –127 to +127
Automatic calibration of the modem’s internal reference is accomplished by inserting a known
high accuracy reference at the rear panel “External Reference” input and enabling the <Unit:
Test – Cal Ref> item. The calibration should take several seconds and will indicate a successful
completion. If the calibration fails then the external reference was out of range in either level or
frequency.
The factory calibration may be restored by setting the <Unit: Ref – Fine Tune> value to “0”.
When entering this parameter via a terminal connected to the remote port the Unit ID Name is
entered directly as text from the terminal keyboard. The Unit ID can also be entered via remote
control at the rear panel DB9 or USB control ports.
After any entry mode the processor will center the input characters on the lower line of the LCD
display
When the unit is powered-up again the main modem processor will automatically query the new
interface card and determine the type and options installed.
Most option interface cards completely co-exist with the on-board interface types, allowing the
optional interface to
represent one or more Rear Connector Plate
added interface types
available. Only one
interface type is however
allowed to be enabled at External Connector Area
one time.
provides additional front panel and remote control parameter settings allowing control of the
option.
The modem’s two FEC slots are identical, and if similar functions exist on two cards the modem
will select a requested FEC option from the first slot which has that capability
In some cases when options are first introduced a software update to the modems internal
program is necessary to allow use of the option. Refer to Section 4.3 “Updating Modem
Software”. The Datum Systems’ M500 Update program will also recognize and install software for
FEC cards present in the modem.
The physical arrangement of the two FEC slots is shown in Figure 2-x below. The same PWB is
used for the standard Viterbi, Trellis Code Modulation and Reed-Solomon FECs with the
manufacturing option to add either the TPC4k or TPC16k chips when ordered. If these options
are ordered later a new board is supplied that has all of the necessary FEC capabilities and the
original standard FEC may be removed. FlexLDPC has a unique PWB, but comes standard with
Viterbi, Trellis Code Modulation and Reed-Solomon FECs, and is configurable to add either the
TPC4k or TPC16k chips when ordered.
2.11.1 Turbo Product Codes Option Installation
The PSM-500 Modem contains on-board circuitry and connectors for adding a Turbo Product
Codes Option Card. This card can co-exist with the IBS Multiplexer (and the Reed-Solomon
function also, but both cannot be used simultaneously).
Turbo Product Codes or TPC is available in multiple mechanical forms and also versions
depending on the link requirements. The three versions are a TPC4K which uses the same TPC
chip as in the PSM-4900 series of modems, and a TPC16K which uses a newer 16K block size to
improve performance, and a TPC-20K board with both the TPC4k and TPC16k chips installed.
Because of the larger processed block size, the TPC16K device has much higher delay or
latency than the 4K block device. It is also more expensive.
The modem can be ordered with any of these TPC options from the factory, and will then
normally be supplied as added components on the standard FEC card already containing the
Viterbi, TCM and Reed-Solomon FECs. Only one of these four versions can be installed on the
standard FEC card, and the type cannot be changed.
The other possibility is to add a card which has one of these two TPC chips into the Slot B of a
modem which already has Slot A occupied by the standard FEC card. Installation of these cards
is into a common SO-DIMM, 144 pin socket, and should be installed only by a qualified
technician.
The modem automatically recognizes the presence of the option card(s) and capabilities and
provides additional front panel and remote control parameter settings to control the option.
The Turbo Product Codes option, when enabled, replaces the convolutional encoder/Viterbi
decoder functions. The Modulator (Transmit) and Demodulator (Receive) functions of each option
are also independent and can be enabled and disabled as required.
Top and side views of the FEC cards are shown in Figure 2-5 below. For additional information
on the installation and configuration of the Turbo Product Codes option refer to Appendix TPC.
Interface Option
Connector
Top View
DRA05-002
FEC Slot B
FEC Slot A
Flash
TPC4k
FPGA TPC16k
Side View
Showing Insertion
Main PCB
Chapter 3 - Operation
3.1 Operating Procedures
Operation of the PSM-500 Modem consists of controlling the unit’s operating parameters and
monitoring status and responses via one of the control interfaces. There are three possible
control methods for the modem:
1. Front Panel Keypad Control. (Section 3.1.1)
2. Terminal Mode Control via rear panel 232/485 or USB control ports. (Section 3.3)
3. Command Interface Binary Control via rear panel 232/485 or USB control ports.
(Section 3.4)
Any of these methods may be used separately or together to monitor and control the modem unit.
Each of these three interfaces and their respective methods are discussed separately below in
the sections noted above.
Additional operating procedures are also presented later in this section on using some of the
unique features of the PSM-500 that would not normally be set-up during installation. These
include such items as the FIFO buffer, built-in BERT, storing and recalling configuration
information, AUPC, the analog monitor output, redundancy and automatic recovery.
3.1.1 Front Panel Control
The front panel of the PSM-500 allows complete control and monitor of all modem parameters
and functions via a keypad, LCD display and status LEDs.
3.1.2 Front Panel Layout and Features
The front panel layout shown in Figure 3–1, identifies the location and labeling of items on the
front panel. The front panel is divided into three functional areas: the LCD display, the Keypad
and the LED Indicators, each described below.
3.1.2.1 Front Panel LCD Display
The front panel display is a 2 line by 16 character LCD display. It is augmented by the four LED
highlighted legends to the display’s right. The display and legends are lighted and the brightness
can be set to increase when the front panel is currently in use, automatically dimming with
inactivity. The display has four distinct areas showing current information. The four legends
indicate the Modem’s functional area that is currently being monitored or controlled, including
“Unit”, “Mod”, “Demod” and “Interface”. The upper left of the LCD shows the current area of use,
such as “Status”, “IF”, “Data”, “Alarm” or “Test” (for the Mod and Demod). The upper right shows
the current parameter being monitored, such as “Frequency”, “Offset” or “Bit Rate”. The lower line
shows the current value of that parameter. The LCD display is a single entry window into the
large matrix of parameters which can be monitored and set from the front panel. It is convenient
to imagine the matrix as 3 dimensional spreadsheet just like a multi-sheet Excel workbook, with
the different “sheets” selected by the buttons for Unit, Mod, Demod and Interface, while
navigation on a given sheet is accomplished using the up, down, left and right arrow keys.
The backlight brightness can be set for two states: Active and Idle. The active state is entered
whenever a key on the front panel is pressed, while the idle state occurs after approximately 60
seconds of inactivity. Each state may be set to “Off”, 1/3 brightness, 2/3 brightness and full
brightness. The default setting is full in the active state and 1/3 in the idle state. To change the
settings for either state go to the “Modem LCD Active” or “Modem LCD Idle” brightness
parameter and adjust to the desired values.
Page 3-3
Operation
Operation PSM-500/500L/500LT SCPC Satellite Modem
Matrix
Matrix Row
Column
Unit
Data Bit Rate Mod
256.000kbps Dem
Int'f
manual as <Mod: IF – Level>. We may also show selection of a specific value for the parameter
using the notation <Function: Column – Row> = value(#). The value is descriptive and the # in
parenthesis is the selection number key to press for optional parameters, if applicable, in the
direct entry mode explained below.
It is convenient to imagine the matrix as 3 dimensional spreadsheet just like a multi-sheet Excel
workbook, with the different “sheets” selected by the buttons for Unit, Mod, Demod and Interface,
while navigation on a given sheet is accomplished using the up, down, left and right arrow keys.
Until you become familiar with the location of parameters using the front panel, it is convenient to
use the Matrix Tables 3-1 through 3-4 as a quick reference.
3.1.3.2 Monitoring Modem Parameters
Any available modem parameter is monitored by simply using the function and arrow keys to
display the desired parameter in the LCD display. The item displayed will remain until changed or
power is removed from the modem unit. The display is “Live”, therefore when a currently
displayed parameter changes the display will change without operator intervention. When
multiple parameters could be displayed (such as when multiple test modes are currently running
or multiple alarms are present) only the highest priority item is displayed. When that item is no
longer valid the next highest priority is displayed. The priority of items is fixed within the modem
software.
3.1.3.3 Changing Modem Parameters
To set any parameter, the 4 functional area keys and the 4 arrow keys to the right of the LCD
display are first used to select the parameter to be set, then one of several “entry” modes is used
to change the parameter. In any entry mode pressing the “Edit” key to indicate a new entry, then
editing the parameter via the arrow keys and the numeric keypad and finalizing the data entry
using the “Enter” key will work. The “Quick” entry mode allows direct entry of a new value without
first pressing the “Edit” key. All entry items take one of two forms:
1. Numeric entry such as frequency or bit rate; and
2. Selection from a list such as selecting FEC rates 1/2, 3/4 or 7/8.
Numeric entries may be entered by performing one of the following:
• When a numeric parameter is displayed, it can be changed by pressing the “Edit”
key, then using the left and right arrow keys to select the first digit to be changed and
entering a new digit. Successive digit entries go to successive characters on the
display, skipping over the decimal point which is in a fixed location. Leading zeros
must be used to enter smaller numbers than are currently displayed, and trailing
zeroes are used to eliminate trailing digits not required. The entry is finalized by
pressing the “Enter” key.
• An alternate edit mode is accomplished by first pressing the “Edit” key, then using
the left and right arrow keys to select the first digit to be changed. The digit is
“scrolled” using the up and down arrow key. Additional digits are pointed to using the
left and right arrows and also scrolled. Finish the edit by pressing the enter key.
Overflow when scrolling up through 9 will increment the next higher digit while
underflow will decrement the next higher digit.
• Direct entry can be accomplished if the <Unit: Keyboard – Entry Mode> is set to
“Quick”. In this mode the current parameter can be changed by simply entering new
information, which completely overwrites the existing parameter. For example when
viewing the Modulator Data Bit Rate of 256.000kbps entering the digits 47.243
(including the decimal point) and pressing “Enter” will change to that new data rate.
Note that a leading “0” did not have to be entered to overwrite the “2” of the existing
parameter.
The current input can be canceled by pressing the “Clear” key at any time before pressing
“Enter”. Failure to press a key for approximately 60 seconds results in automatic canceling of the
current entry and return of the display to the current setting.
Selection entries may be accomplished by one of the following:
• When a selection entry parameter is displayed, simply press the “Edit” key followed
by a digit key 0, 1, 2, 3 or 4. In this scheme “0” represents disabled, OFF, NO or the
first possible choice. “1” represents enabled, ON, YES or the second possible choice.
“2”, “3” and “4” represents the third, fourth and fifth possible choices. Then press the
“Enter” key to finalize the entry.
• Alternately, when a selection parameter is displayed it can be changed by pressing
the “Edit” key, then using the up and down arrow keys to scroll through the possible
choices. When the desired option is displayed, pressing the “Enter” key selects the
displayed choice and finalizes the entry. When scrolling though the available options,
an arrow in the left column position denotes the current setting.
• Direct entry can be accomplished if the <Unit: Keyboard – Entry Mode> is set to
“Quick”. In this mode the current parameter can be changed by simply entering digit
key 0, 1, 2, 3 or 4 … and pressing “Enter” to finalize the entry. Optional selections
can be viewed by successively pressing several keys to determine their value, then
pressing “Enter”.
Following a valid input, the modem will place the new setting into the nonvolatile EEPROM
making it available not only immediately, but also automatically the next time the unit is powered
on.
3.1.3.4 Automatic Modem Parameter Sequences
Certain parameters are dependent on other parameter settings. New in the PSM-500 is
automatic presentation of those parameters that must be set to properly achieve the first setting
entered. An example of this is when entering an “IF Modulation” mode change, the modem will
accept that but next request entry of the “Data FEC” type, then the “Data Code Rate” finally
returning to the original IF Modulation screen. If only the Data FEC type were initially changed
then only the following item in the sequence would be requested. This insures that all of the
necessary parameters are entered to enable any mode dependent on other settings. Normal
settings are typically displayed during this sequence and it may be possible to simply press the
“Enter” key at each succeeding request.
3.1.3.5 Finding Modem Parameter Limits
During parameter setting you may not know what the maximum or minimum value is that may be
entered. The modem can help in some cases by taking the parameter to its maximum or
minimum value when you enter a value greater or less than possible. For example, when all other
parameters have been set, if you wish to go to the maximum transmit data rate possible in an
M505 modem simply enter a value like 10000 (for 10,000 kbps). The modem should beep, say
“Set at max” and enter a value of 5000 (for 5 Mbps).
The top gray row represents column headers, which are shown on the LCD display in the upper
left. Items below the header are row parameter names shown in the upper right of the LCD.
Columns are navigated using the left and right arrow keys while rows are navigated using the up
and down arrow keys.
The tables below are organized with general “Rules of Thumb” which aid navigation.
1. The “Status” columns are generally read only, providing status on specific areas of
modem operation.
2. The Modulator and Demodulator matrixes use common column designations. A current
parameter in one area can be immediately accessed in the other by pressing the
appropriate “Mod” or “Dem” button. For example when viewing the Mod Bit Rate, the
Demod Bit Rate is accessed by simply pressing the “Dem” button.
3. The “Alarm” columns existing in all four matrixes and represents the disposition of alarm
information from that source. Therefore the <Dem: Alarm – CXR Lock> sets the
disposition of the Demodulator Carrier Lock Alarm as either None, to Alarm Relay A, to
Alarm Relay B, or to Alarm Relay A & B.
4. The “Test” columns existing in all four matrixes and represents the control and display of
test information for that area. The top entries in the Test column contain tests which can
be enabled or disabled if available. The lower rows represent measurements of
parameters and are read only. Active tests enabled in these columns generate flashing
“Test” LED lamps in appropriate areas.
Table 3-1
PSM-500 Front Panel Parameter Matrix – Unit Sheet
Status Redundcy Config Keybrd Remote USB Ref Monitor Alarm Test
Modem Mode Modem Mode Mode Mode Source Mode Reference Modem
Reference SW Rqst Recall Entry Protocol Activity Frequency Full OCXO Oven Cal Ref
Redundcy SW Hold Store LCD Actve Address Fine Tune Zero Tst Active Update ROM
Unit ID Backup Restore 1 LCD Idle Rate Hardware Ref AFC
Model Restore 2 LCD Cntst Format Beep SysClk AFC
Feature Restore 3 Activity Port +3.3V
Serial # Restore 4 Activity +5.0V
Version Restore 5 +12.0V
FEC A Restore 6 +21.0V
FEC A Ver Restore 7 -12.0V
FEC B Restore 8 Boot Code
FEC B Ver Power-Up
Mod Opt
Int’f Opt
Notes:
Parameters shown in gray are only available when the entry immediately above is enabled or set to a mode that requires those
entries. The gray Redundancy parameters are only shown when connected to another unit in redundancy mode.
Other columns may be added by options added to the modem or software.
Word spelling is purposely truncated to fit in available LCD display window.
Table 3-2
PSM-500 Front Panel Parameter Matrix – Modulator Sheet
Status IF Data Mux BUC Alarm Test
CXR Frequency Bit Rate Mode Power CXR Modulation
Data Offset Fec ESC Overhead Voltage Out Data Symbol Rate
Clock Level FEC Options MCC Overhead Voltage Min Clock Clock Error
Test Output Code Rate OverHd Ratio Current Out AUPC CXR ALC
Modulation RS Mode ESC Port Current Max Tst Active LO AFC
Spectrum RS (n) ESC Rate Current Min Hardware Step AFC
Filter Mask RS (k) ESC Frmt 10 MHz Ref BUC Power
Mode RS Depth ESC CTS LO Frequency
Table 3-3
PSM-500 Front Panel Parameter Matrix – Demodulator Sheet
Status IF Data Mux LNB Alarm Test
CXR Frequency Bit Rate Mode Power CXR Lock IF Loopbck
Eb/No Sweep Range Fec ESC Overhead Current Out Data Symbol Rate
Offset Sweep Mode FEC Options MCC Overhead Current Max Low Eb/No Clock Error
Level Sweep Time Code Rate OverHd Ratio Current Min Low Level AGC
Est.BER Modulation RS Mode ESC Port 10 MHz Ref Tst Active LO AFC
SER Spectrum RS (n) ESC Rate LO Frequency Hardware Step AFC
Buffer Filter Mask RS (k) ESC Frmt Backward IDcOff
Test Eb/No Alm RS Depth ESC DTR LNB Power QDcOff
Low Level Alm Dif Decoder ESC DSR
Impedance Descrambler
Clk Source
Buffr Delay
Buffer Size
FEC Hold
Table 3-4
PSM-500 Front Panel Parameter Matrix – Interface Sheet
Tables 3-5 through 3-8 describe the parameters available from the front panel and entry in more
detail. The grayed separators delineate column divisions in the area matrix. The “»”symbol
indicates that this parameter is not available unless a preceding parameter is enabled or set to
require those parameters, or optional hardware is installed that uses that particular parameter.
Parameters can also be added as new options are installed.
Data Bit Rate Numeric 1.200 to 20,000.000 kbps Modulator Bit Rate – The max
2.100000Mbps in 1 bps resolution. Entered and min are determined by
in kbps to 1bps increments. settings and options.
Data FEC Selection 0 = Viterbi, TPC Decoder - Only available
Viterbi 1 = TPC Full if installed. Reed-Solomon is
2 = TPC Short enabled in R-S column.
3 = TPC (Legacy) Legacy in Rate ¾, 7/8 only.
4 = TPC (CT) CT compatibility Rate ¾ only.
Data FEC Option Selection 0 = Normal, FEC Optional Modes. May
Normal 1 = Swap C0/C1, change depending on FEC
2 = Invert C1, options installed.
3 = Swap and Invert C1
Data Code Rate Selection 0 = ½, 1 = ¾, 2 = 5/6 FEC Code Rate. The options
Rate 1/2 3 = 7/8. may change depending on
0 = 2/3 in 8PSK TCM FEC installed and selected
R-S Mode Selection 0 = Disabled, Reed-Solomon column and
IESS-308 1 = IESS-308 options only available if not
2 = IESS-309 disabled. Entry is not shown
5 = IESS Custom when TPC enabled.
»RS FEC (n) Numeric In Custom Mode only: Block size
126 Available n values n = 22 to 255
Read only in other modes
»RS FEC (k) Numeric In Custom Mode only: k = 20 to 253,
112 Available k values k must be 2 to 20 less than n
Read only in other modes
»RS FEC depth Selection In Custom Mode only: Interleave depth factor
4 0 = 4, 1 = 8, 2 = 16
Read only in other modes
Data Dif Decoder Not 0 = Disable, 1 = Enable Differential Encoder Not
Enabled Shown shown or settable except in
special modes.
Alarm Tst Active Selection 0=None, 1=A, 2=B, 3=A & B Selects destination of alarm
to Alarm A
Alarm BER Loss Selection 0=None, 1=A, 2=B, 3=A & B Selects destination of alarm
to Alarm B
Alarm SnIP Selection 0=None, 1=A, 2=B, 3=A & B Selects destination of alarm
to Alarm B
** Interface Status when the SnIP option is installed and enabled can be:
Unit Status
Modem Demod Tst Active
Reference Internal, Ok
C) Redundcy Internal 1:1
D) Unit ID
Model PSM-500
Serial# 13490
Version 0.10
Assuming that we wanted to view another of the Unit column screens. If we first press the “0” key
to indicate that we want to change to a “Unit” screen the following lower screen prompt will be
displayed:
PSM-500 VT100 Terminal Control
Unit Status
Modem Demod Tst Active
Reference Internal, Ok
C) Redundcy Internal 1:1
D) Unit ID
Model PSM-500
Serial# 13490
Version 0.10
Notice now that we can select from the Status, Configuration, Keyboard, etc. columns of the Unit
Matrix. Selecting for example the “Test” item (selection 9), would display the following new
screen.
Unit Test
A) Modem BER Test
B) Cal Ref Disabled
Ref AFC +1.1V
SysClk AFC +9.3V
+3.3V Power +3.3V
+5.0V Power +5.0V
+12.0V Power +12.0V
+21.0V Power +20.8V
-12.0V Power -12.2V
J) Boot Code 0000:0000:0000
Notice that some items have a preceding letter with parentheses. These items are programmable
via the communications interface. Items without a preceding letter in parentheses are “Read
Only” items.
Any available “screen” can be displayed with only two keystrokes. These are similar to
designating the functional area and column of a matrix as when using the front panel.
3.5.1 Power-Up
On initial and every subsequent power-up, the modem microprocessor will test itself and several
of its components before beginning its main monitor/control program. These power-up
diagnostics show no results if successful. If a serious power on failure is detected, the ALARM
LED is flashed at an approximate 4 Hz rate. Other failure modes are displayed on the front panel
LCD.
New modems from the factory have default values placed into the EEPROM for operating
parameters. If a Monitor/Control System does not configure the modem automatically via the
serial command channel, the modem can be easily configured from the front panel or can be
connected to a VT100 protocol terminal to set the modem's operating parameters. To restore the
default parameters the modem can be powered on while depressing the “Clear” key.
The most common default parameters placed into the EEPROM are as follows: A modem can be
returned to the factory default settings by using the front panel command <Unit: Config -
Recall>, then editing (or quick edit) and choosing the “Factory” or “0” selection option.
Modulator: Demodulator:
Carrier Frequency = 70.00 MHz Carrier Frequency = 70.00 MHz
Data Rate = 256 kbps Data Rate = 256 kbps
Modulation = QPSK Modulation = QPSK
Code Rate = Rate 1/2 Code Rate = Rate 1/2
Differential Encoder = Enabled Differential Decoder = Enabled
Scrambler = Auto Descrambler = Auto
Clock phase = Normal Clock phase = Normal
Data = Normal Data = Normal
Clock Source = Internal Clock Source = Receive
RTS = Ignore Sweep mode = Fast
Carrier = Off. Acquisition Range = +/- 30 kHz
All Mod Alarms to Relay A All Demod Alarms to Relay B
Modem Unit: Interface:
Modem Reference: Internal, 10 MHz Mode = RS-449
Remote Port Address = 1 All Tests Off
Remote Port = RS-232 Data and Clocks in normal mode (not
Remote Mode = Binary Packet inverted). The XMT Clock now uses a
Remote Rate = 9.6 kbps default “Auto” mode that detects the
Remote Data Format = 8 data bits, 1 proper phasing and applies it.
stop, no parity
In a properly operating system, with an incoming carrier available for the demodulator, the
modem’s Alarm (red) and Warning (yellow) LEDs should all go out. Without an acceptable
incoming carrier the Demod “Major Alarm” and “Summary Alarm” will illuminate. When the
incoming carrier is acquired, the green “Signal Lock” LED should illuminate. The “Transmit On”
LED will also illuminate if the transmit output is enabled.
Function Description
AUPC ENABLE/DISABLE Enables/Disables the AUPC to function locally.
MOD AUPC Eb/No Desired Eb/No of remote modem.
MOD AUPC MIN LVL Sets minimum output power to be used.
MOD AUPC MAX LVL Sets maximum output power to be used.
The basic AUPC operation is described as follows: Assume that the two modems, one at each
end of the link, are set up for AUPC operation. Only one direction is discussed, controlling the
Eb/No at Site B, but the same functions could be occurring in both directions simultaneously. This
is shown in the Figure 3-4 below. Modem “A” is transmitting to modem “B” under normal
conditions and modem “B” has a receive Eb/No of 7.5 dB. Modem “A” has been set to an AUPC
Eb/No on the front panel of 7.5 dB, and is currently outputting –15 dBm. Next it begins raining at
location “B”, and the Eb/No drops to –7.0 then –6.8 dB. Modem “B” is constantly sending update
messages to “A” and reports the current Eb/No. When “A” sees the drop in Eb/No, it slowly
begins to raise the output power, and raises it again when it sees further drops. As the rain
increases in intensity, and the Eb/No decreases again, “A” continues to increase its power level
to compensate, and when the rain diminishes and quits, it also lowers its power level to
compensate. The operation is therefore a feedback control loop with the added complication of a
significant time delay.
Satellite
Site A Site B
Modem A
Modulator Modem B
Modulator
AUPC Control
Mux
Eb/No
Eb/No
Mux
Modem A Modem B
Demodulator Demodulator
There must be safeguards built into the AUPC system. First, the Modulator has two additional
parameters which allow control of the maximum and minimum power output level. The other
controls are built into the operating control software to limit response times and detect adverse
operating conditions.
The link should now be operating and using AUPC to set the A transmit level keeping the B
receive Eb/No constant. Alarms will be generated if the transmit level reaches either the max or
min level attempting to maintain the receive E/b/No.
The exact settings required can be further adjusted to account for the type of fading expected.
For example if in a tropical environment with sudden heavy showers you may want to allow more
power margin and possibly speeding up the response time by using a higher speed MCC
channel.
To set the other direction to use AUPC, simply repeat the above instructions reversing the A and
B site.
3. External FIFO Clock – (Option 2) This option allows a station-derived standard clock
rate to be used to clock data out of the FIFO. The externally supplied clock must be
equal to the average receive data rate.
4. Modulator Clock – (Option 3) Uses the modulator data rate clock as the output
clock and obviously requires that the modulator and demodulator data rate be
identical.
The Receive FIFO operation can be set from the front panel or remote control, and consists of
selecting the output clock source, and either the delay time desired in milliseconds or the number
of bits of delay. The processor computes the other value based on the one entered and the
current data rate. The modem processor also keeps track of and can display the current FIFO fill
percentage status. The FIFO sets the delay or number of bits selected upon activation and this
center value represents 100% FIFO fill. At any time the FIFO may contain from 0% to 200% of
the set value. The percentage fill can also represent the percentage of delay with respect to the
setting. For example if the buffer was set to 2 mS of delay and the fill is 150% this represents 3
mS of delay.
When the data rate is changed the modem maintains delay time constant, automatically changing
the number of bits stored in the buffer to compensate.
NOTE: When the number of bits of delay are very small, one bit may represent a large
percentage change (e.g. if the delay is only 4 bits, each bit represents 25%). The delay
may be set from 4 bits to 131,070 bits at any data rate, resulting in a delay ranging from
0.00081mS (4 bits at 4.92 Mbps) to over 42,000 mS (131,070 bits at 2400 bps).
An overrun occurs when a bit is clocked into the FIFO causing the fill to reach a full 200% of the
selected value. This causes flushing the upper half of the FIFO, restoring the fill to 100%, re-
centering the FIFO. The data flushed is lost and cannot be recovered.
An under-run occurs when the last bit is clocked out of the FIFO, emptying it. This also causes
re-centering of the FIFO by resetting the buffer pointers to the mid or 100% level, resending all
the data in the buffer. Both conditions result in a potential serious disruption of traffic.
When an under or over-run occurs an internal modem flag is set indicating that a re-center has
occurred. The front panel display shows “Slip” and FIFO fill data percentages read from the
remote port are negative numbers. This latched flag may be reset at the front panel or by writing
to the remote port FIFO parameter.
The FIFO may also be re-centered at any time on command from either the front panel or via the
remote control. At the front panel the command is <Dem: Status - Buffer> and pressing the “1”
key, then "Enter" to confirm. Pressing the “0” key on this parameter will clear the “Slip Status”.
In “framed” communications the severity of the disruption can be minimized by setting the buffer
size in bits to multiples of the frame size. For example if the total frame size is 512 bits and the
buffer is set to a size of 1024 bits an under or over-run would result in the frame flags remaining
in the same location in the data stream. Note that frames will still be errored by the under or over-
run, but synchronization may not be lost. If a superframe structure is used it is likely that
synchronization will still be lost.
• Advantage – The second or current back-up unit can be sent its full configuration from
the on-line unit, making set-up extremely easy.
• Advantage – Since the units are fully programmable concerning alarm content that
determines the switching criteria, this method is more flexible than most redundancy
schemes.
• Advantage – The single point failure of the switch in a classic 1:1 redundancy scheme is
eliminated. Since these switches are often mechanical relays they actually have a poor
failure rate, reliability (with respect to a classic scheme) is not seriously compromised.
• Disadvantage – There is no separate physical switch which provides a positive lock-out
of a seriously failed unit that may not be able to turn its output signals off.
• Disadvantage – There is no single point control allowing forced switching away from one
unit. Forced switching is accomplished only “from” the currently on-line unit.
• Disadvantage – There is no mode forcing a priority unit. In a priority system one unit is
considered primary and the other secondary. If both units show good status the primary
is always on-line. But, the priority scheme would also create more switching and is not
normally used anyway.
Of course the major advantage to the built-in redundancy capability is its extreme low cost.
programmable itself. For most applications though the default “On Any Alarm” is a
preferred selection.
• <Unit: Redundncy – Sw Hold> This parameter determines how long an alarm must
exist on the on-line unit and not the off-line unit before switching will occur. Allowable
values are 0.0 to 600.0 seconds. The value could be set to zero, but this is not advised. A
nominal value of 0.5 seconds insures that intermittent cases do not cause undue
switching. A built in factor of 10 seconds is provided once a switch has occurred before a
switch back to the original unit is allowed (except in the case of a manual switch request
or loss of power in the on-line unit which requires 2 seconds).
The possible case can arise when both units go out of alarm at virtually the same time. This might
occur if both units are powered on simultaneously or the receive carrier appears after being off or
a necessary clock signal is applied to both units. In such tie cases, which unit will be placed on
line is determined by the unit serial numbers, where the highest serial number wins the tie.
• The unit currently Off-Line will present its status on the lower line of the LCD display as
“Standby OK” or “OFFLINE – ALARM”.
⇒ CAUTION: Enabling the BER Test set will result in disruption of any traffic currently
through the PSM-500 in the direction that is enabled. BER Tests should not be performed
on a live traffic unit.
The PSM-500 BER Test set can be “pointed” in two possible directions. The normal mode as
available in the PSM-4900 involves the BER transmitting in the direction of the satellite and
receiving from the satellite direction. An alternate mode allows the BER set to transmit and
receive toward the terrestrial data interface or “line” side. The direction is controlled via the
Interface <Intf: Test – BER I/O> parameter and can be selected for either “Satellite” or
“Terrestrial”. The Satellite direction looks to the modem as if a DTE is sending and receiving data.
The Terrestrial direction appears to the line as if a DCE device is sending and receiving data.
The use of the BERT is more fully described in the Maintenance Section 4.1.2.
The analog output presented at the rear panel Alarm connector J5 has a 1kΩ output impedance,
protecting the driver circuitry from shorts.
⇒ Note: The ACR is not available when the modem is operating in a redundancy mode.
Several examples more clearly illustrate the use and operation of the automatic configuration
recovery (ACR).
Consider a demand access type system where modems not currently in use are intended to be
placed at a “home” location. This would consist of mainly a receive IF frequency and data rate
where the modem could receive assignment information. By storing the necessary parameters for
the home location in configuration #1, and setting the configuration #1 time to 10 seconds, the
modem will return to home whenever no carrier is received for 10 seconds. Then upon receiving
an assignment, going to the new assigned set-up, and passing data traffic the link “tear-down”
only requires removing the inbound carrier. 10 seconds later the modem will return to the home
location awaiting another assignment.
Consider a simpler system that uses the multiplexer option to remotely program a far end
modem. This ability is only available via remote control, not the front panel. If a remote
unattended modem is erroneously commanded to a location and does not find the carrier then it
may be impossible to “re-acquire” that modem, necessitating a technician to visit that site. By first
storing the current configuration in one available location, and then setting the time to perhaps 30
seconds (all over the link itself) for that configuration then the remote modem can safely be sent
a command to change frequency (for example) knowing that if the modem does not lock up to a
receive carrier in 30 seconds it will return to the current configuration.
Multiple configurations can have time settings associated with them. The result is that each
configuration will be tried in turn until a carrier is found and locked. Upon losing the receive
carrier again the modem will restart the configuration sequence beginning with the lowest
numbered configuration having an associated non-zero time. The sequence is repeating with the
highest configuration with a non-zero time “wrapping” around to the lowest.
Caution – What is not immediately obvious is that the time set is the time of the “current”
configuration with no carrier before switching to that configuration. Thus if configuration #1
is set to 12 seconds and #4 is set to 2 seconds (all others being set to zero) then when on #4 for
12 seconds with no receive carrier the modem will change to #1, and when on #1 for 2 seconds
with no receive carrier then the modem changes to configuration #4.
Note that all of the above examples would be “safer” if the <Dem: Alarm – CXR Lock> is set to
“Mute and …”. With this setting the transmit carrier is turned off when no receive carrier is
present, even if commanded on.
2. The modulator responds to the DTE device when ready to transmit by activating the
CTS signal.
3. Any time after the CTS is received by the DTE, the DTE starts transmitting flags
and/or data. The first non–SDLC/HDLC flag character received by the modulator is
the start of transmission signal, causing the modem to generate a preamble and
initiate the “Carrier ON” command. Transmission continues with data bytes placed
after the preamble.
4. The next SDLC/HDLC flag received by the modulator is the end of transmission
signal.
5. When the closing flag is detected by the modulator, it drops the CTS indicating that a
new data message cannot be started. When the last data bit is sent, the modulator
will reassert the CTS signal, and turn the carrier OFF.
Chapter 4 - Maintenance
4.0 Periodic Maintenance
The PSM-500 requires no mandatory periodic field maintenance procedures. The unit contains
no adjustments and most calibration is digital and held in EEPROM. Should a unit be suspected
of a defect in field operations after all interface signals are verified the proper procedure is to
replace the unit with another known working modem. If this does not cure the problem, other
equipment in the link, wiring or power should be suspect.
There are no batteries or parts requiring periodic service contained within the case. The only
moving part is the internal fan, which is designed for a service life in excess of 200,000 hours.
There is no external fuse on the PSM-500 Modem. The fuse is located on the power supply
assembly inside the case, and replacement is not intended in the field.
transmit a data signal at one end of the link and sequentially set each of the loop-back options.
Proper reception of the loop-back data verifies all components between the source and the loop.
The simplified diagram below shows the location of the PSM-500’s built in loop-back functions
within the link from one end of a link to the other. The advantage to having these functions built-in
is that they are electronically programmable without having to disconnect existing cabling to
connect equipment that must be available for testing.
Built-in BERT is
Satellite
located here.
Link
Each of these loop-back modes are individually programmable at the modem front panel or
remote control interface. More detail on each of the typical loop back uses is given below.
• Near End Terrestrial Data Loop-Back: This will be the closest loop-back to the DTE or
BERT. If data is returned and received properly it indicates that the DTE wiring and
connection to the modem are correct. Note from the position of the built-in BERT in the
diagram above that this test requires an external source of data. The PSM-500 can
individually set the data path terrestrial side loop-back and the data path satellite side loop-
back in <Int’f: Test - Ter Loopbck> and <Int’f: Test - Sat Loopbck> respectively.
• Near End IF Loop-Back: This second loop-back will verify the modem transmit data signal
processing, modulation, demodulation, receive signal processing, and connection to the
receive interface. The PSM-500 sets the IF loop-back in <Dem: Test - IF Loopbck>. Note in
this test that the near end satellite loop-back function should not be enabled whether using
the internal or an external BERT.
• Far End Satellite Data Loop-Back: This will test most of the satellite link as well as the
functions checked in test 2 above. The signal is sent over the satellite (or test setup) and is
looped back at the satellite side of the data interface on the far end. This tests both modems,
the satellite link and originating end wiring. The PSM-500 sets the satellite side loop-back in
<Int’f: Test - Sat Loopbck>. Note in this test that the near end satellite and IF loop-back
functions should not be enabled whether using the internal or an external BERT. Setting this
mode slaves the modulator timing to the demod timing and the FIFO buffer remains engaged
if enabled.
In this type of testing an external BERT is typically set to provide a terminal timing output, while
the connected modem is set to use the terminal timing signal as the transmit bit rate clock
source. This modem can alternatively be set to use its internal clock for the transmit clock timing
and provide that signal to the BERT for synchronization. More information on using the PSM-
500’s internal BERT is given below.
All of these settings and test results are also available via the remote control interface, allowing
for automated and periodic testing of units not in service.
4.2 Troubleshooting
The following is a list of possible problems that could be caused by failures of the modem or
improper setup and configuration for the type of service. The list is arranged by possible
symptoms exhibited by the modem. When simple solutions yield not results then test equipment
may be necessary to help isolate the trouble. A spectrum analyzer is invaluable. So is a Bit Error
Rate Test set (BERT). The PSM-500 has a built in BERT function.
In most cases the first attempt at isolating a problem suspected of being within the modem is to
place the modem in the Self-Test Mode. Since this the vast majority of internal circuitry then a
pass on this test means that the user should probably concentrate on parameter settings and
external equipment and connections.
One obvious and time-honored method of isolating problems is to substitute suspect equipment
with known good equipment. Assuming that the configuration setting of the equipment is not the
source of the problem, this method will quickly eliminate items from the potential source list. The
two drawbacks to this method are the availability of extra equipment and the possibility of
interaction between two or more equipment items.
Possible Cause: Receive Carrier signal Eb/No is too low resulting in poor BER
performance.
Action: Ensure that the transmit end is properly set and that the receive subsystems are
all operating correctly. In a small station ensure that the antenna is “peaked” on the
satellite. In a Ku-Band station, intense rain can cause poor receive performance.
Possible Cause: Transmit and Receive scrambler or differential encoder options do not
match or not enabled. Note – The differential encoder in the PSM-500 is under processor
control only, but this cause could apply to a mixed system linked to another modem.
Action: Check the current state of the Scrambler and differential encoder. In all operating
systems the differential encoder/decoder and one of the available scramblers must be
enabled.
Symptom: The Modem receive FIFO buffer indicates “Slip”.
Possible Cause: The FIFO automatically re-centers when an overrun or under-run
condition occurs.
Action: Check that the proper clocking options are used and the FIFO buffer is set large
enough to handle the expected satellite Doppler shift over a 24 hour period. No amount
of buffering will correct for different clocks on the input and output of the FIFO.
Symptom: Receive DTE equipment indicates “clock slip” or “sync lost”.
The complete software update “package” consists of two or three ZIP compressed files – One
holding the Update program with a Window’s Installer and the other two holding the firmware
images that the Update program writes to the modem. There are separate firmware files for the
main unit and the FEC card The following are typical of the file types and ZIP contents, but they
may change as to provide easier operation – check the web site for the latest:
A. - M500UpdateFullVxxx.zip where xxx is the current version number of the M500Update
program. Besides the Loader program itself this zip file also contains the full set of Visual Basic
DLL and OCX associated files. The USB drivers needed for installation on a computer are
typically separately packaged.
Once installed the latest version of the program itself without the other drivers and DLL files is
available as M500UpdateVxxx.zip (note the “Full” is not in this version’s name).
• M500Flash.EXE PC based program to load software to the modem.
• Various DLL, OCX Visual Basic runtime routines necessary to run the M500Flash.exe
program.
B. M500ModemUSBDriver.zip This program is only needed once on any computer to provide
the USB driver.
• USB drivers for the FTDI USB interface – currently named FTD2XX.lib, sys, dll, ini, etc.
• Windows installer used to install the driver program and its associated files.
C. M500Ux.xx.yyy.zip where x.xx is the current version number and yyy is the applicable unit
type as explained below.
• M500Ux.xx.yyy.fbf Binary image of the modem’s main Unit software/firmware.
M500U is for the Unit where currently exists yyy values of:
o 000 for a 70 MHz modem
o 001 for a 140 MHz Modem
o 040 for the L-Band Modems
D. M500Fx.xx.yyy.zip where x.xx is the current version number and yyy is the applicable FEC
card type as explained below.
• M500Fx.xx.yyy.fbf Binary image of the FEC cards firmware. M500F is for the FEC
where currently exist yyy card types of
o 001 for the standard FEC card containing Viterbi, Trellis Code Modulation (TCM)
and Reed-Solomon
o 002 for the enhanced standard FEC card containing Viterbi, Trellis Code
Modulation (TCM) and Reed-Solomon, plus the TPC4K type Turbo chip.
o 003 for the enhanced standard FEC card containing Viterbi, Trellis Code
Modulation (TCM) and Reed-Solomon, plus the TPC16K type Turbo chip.
o 004 Not defined yet.
In addition the user must supply a “PC” type computer running Windows and a USB A to B type
cable to connect the PC to the modem. The USB type A connection goes to the computer and the
type B connection to J10 on the rear of the modem. This is a normal serial cable available from
many common sources and also used with many computer peripherals such as printers. Do not
connect this USB cable until the software drivers are installed.
Although not recommended, if using a serial RS-232 connection to perform modem
updates, the serial cable has a male DB9 connector on the modem end and normally a
female DB9 connector on the computer end. Older computers may require a DB25 to
DB9 adaptor on the computer end. The 9 pin cable is wired 1:1 with no crossovers (as in
“null modem” type cables). This is a standard serial extension cable available at
computer outlets.
Any software upgrade requires a “Control Program” hosted on the computer which transmits or
“Loads” the new software to the modem. The Control Program is available with the newer
software revision. Currently the name of the control program is “M500 Update.exe”. This Loader
is an IBM PC Visual Basic based program that can be run under Windows 98, 2000 and XP. We
now have a newer self contained M500 Update program capable of running under Windows Vista
available on the web site. This version can also check a special web site on demand for newer
firmware for the connected modem, making the process as painless as possible.
The Installation program must be run first to install the update program in the PC used for
updating modem firmware. The M500Update program is specifically designed to stand alone if it
is located in a directory with its VB DLL and OCX files plus the flash binary format files for the
modem. It does not change the registry or appear in the “Start Programs” menu. The advantage
of this is that it can even be run from the CD that comes with the modem (although that probably
does not have newer flash files), or from a central networked computer location.
1. Download the Full version of the update program which includes the program, associated
files and USB drivers. Also download the latest firmware for your modem from the web
site.
2. Unzip or extract the program files into the directory where you saved the download in
step one. An alternative is to leave the downloaded program files compressed - either
WinZip or Windows XP compressed folders will allow you to run the install program
directly from within the compressed file.
3. Run the “Install.exe” file by double clicking on it. This will create the C:\Program
Files\M500 FLASH Loader directory and place the program and associated files there.
The USB drivers will be in a sub-directory named. C:\Program Files\M500 FLASH
Loader\UsbDriver.
4. Unzip or extract the binary files into a suitable folder. You could use the C:\Program
Files\M500 FLASH Loader directory, or chose one within My Documents such as “M500
Binaries”.
5. Connect the computer to the modem via a USB cable. If the modem is turned off then
turn it on. The computer will recognize and advise you that new hardware has been
found and run the new hardware wizard.
6. If the wizard asks if you would like to connect to the Internet to search for drivers, select
“No, not this time” and click “Next”.
7. When asked if you want to “Install Automatically” or “Locate the drivers myself” or “Have
Disk”, select the self locate or have disk option and navigate to the C:\Program
Files\M500 FLASH Loader\UsbDriver folder and there select the ftd2xx.inf file. Then let
windows do the rest. If notified that the driver is not certified select “Continue Anyway”.
The supplied drivers are from a reputable source that manufactures the USB interface
chip.
The modem has a complementary program which talks to the loader and controls re-writing of the
flash memory. No actions to the modem are normally necessary before beginning update with the
exception of removing it from service, and the M500 Flash Update program can take care of all
tasks directly including finding the modem, determining if it has newer software/firmware versions
available and preventing loading of incorrect firmware to the modem The modem is specifically
designed to not accept firmware that is not made for it. For example the standard 70 MHz modem
would reject firmware for a 140 MHz or L-Band Modem.
It is a good idea to see if a later version of the update program or the update instructions are
available on the web. Those could be newer than the basic information given here.
⇒ Note: For virtually all users the recommended program is the newer “M500
Up_date.exe” program available on our web site at www.datumsystems.com. This newer
program in version 2.06 and later is significantly easier to use, works with any version of
Windows including Vista, and can check a special web site for available modem and
program updates on user command. This relieves the user from having to know about
numbering schemes, modem types, etc. Use instructions are also on the web site.
The M500 Flash Update program gives feedback to the user during the update process. If you
suspect that something is not going correctly with the update process then wait until the current
process is completed and contact Datum Systems via email with details of what is observed. We
have tried very hard to make the program as robust as possible.
There are two types of software/firmware files that may be uploaded to the modem. One is for the
main modem itself and its binary file name begins with “M500U”. The other is update firmware for
the particular FEC card that may be installed and its binary file name begins with “M500F”. The
update program is intended to determine which one of these may be required and which one
should be loaded first.
All user settings and calibration data are maintained when newer software revisions are installed.
⇒ CAUTION: The process of updating software will result in disruption of any traffic
currently through the PSM-500. Upgrade should not be performed on a live traffic unit.
⇒ CAUTION: The process of updating software must not be interrupted once started. In
the rare occasions when a new bootloader is installed in flash, failure to complete this
portion of the loading process may result in complete loss of the modem programming. In
this eventuality the modem must be returned to Datum Systems for software initialization
and calibration..
Complete update of the modem normally requires approximately 4 to 6 minutes. The process
cannot be accomplished on multiple modems simultaneously.
Before performing an update check the web site first to determine if there is a later firmware
revision and if there is any advantage to performing the update. The firmware revision on the web
is compared to that in the modem.
To determine the modem’s current Unit firmware revision go to the front panel and navigate to the
<Unit: Status - Version> parameter. It will display a number including two decimal points, for
example 0.09.000 where the 0.09 represents the firmware revision “0.09” of modem type “000”.
In this case the 000 type is a 70 MHz modem. Then if on the web site there is found for example
a firmware updated version number 0.12.000 that indicates that the latest revision available for
the 70 MHz M500 modem is 0.12. The file can be downloaded, unzipped and placed in the
C:\Program Files\M500 FLASH Loader directory where the program can find it. It may alternately
be placed in another directory or folder and you will have to browse to locate the binary file.
And finally the procedure:
1. Insure that the modem is connected to the PC via a USB type A to B cable, and the
modem is powered on. The USB drivers for the modem should have already been
installed.
2. Start the update program via “Start – Programs – M500 FLASH Loader” menu, and
the M500 Flash Loader program should start and recognize the attached modem. In a
few seconds the modem’s serial number and other information will be shown in the left
panel displaying a window similar to that below.
3. Click on the entry box below “M500 FLASH Program File” in the right pane. This will bring
up a file open dialog box. Browse to the location of the flash binary format (.fbf) files
downloaded with the newer firmware version, and select the M500F or M500U file
desired.
4. The program window should now show that file selected, and if it is the same as the
current file loaded into the modem it will display as below:
Not the “** Current Version **” after the File Firmware Version = 0.08.000 indicating the
selected file is the same as that loaded.
5. If the binary file versions available in this directory are newer than those in the modem,
then select the “Update M500 FLASH” button and the update process will begin.
6. When completed the modem will reset itself and the revised information will be displayed
in the left pane. If you need to also load an FEC firmware binary file, then repeat the
process by selecting that file and updating again. When finished simply end the M500
FLASH Update program and disconnect the modem from the computers USB port.
NOTE: The IF version of the 70 MHz, 140 MHz and L-Band modem is determined by
hardware only, and has nothing to do with the software. The modem will refuse to accept
attempts to load the wrong software intended for another version.
OR How Do I?,
Why Doesn’t It?,
and Where Is?
This Section is intended to form a smart index pointing to proper sections of the manual with
information on performing common actions or answering common questions. The presentation
here is divided into 5 common areas – Link Setup, Front Panel, Remote Control, Data Interface
and Manual.
The PSM-500 has several new programmable features which should make this easier than ever.
First, where possible if both modems adhere to Intelsat IESS standards then those defined
parameters should be set the same. Still all modem manufacturers have their own conventions
for setting parameters with no specified standard, so for example some modems may have a
different modulation sense for data bits than others. This would make no difference between two
modems of the same type, but would invert data between modems of different types on each end
of a link. Most items of this type are programmable in the PSM-500 modem.
The PSM-500 also has a significant number of FEC compatibility modes for aid in achieving
compatibility with some competitive modems, especially in Turbo FEC modes. These modes are
denoted by the FEC Option type “CT” on the front panel selection.
Is Datum Systems' Turbo Product Codes compatible with that made by other modem
manufacturers?
The PSM-500 also has a significant number of FEC compatibility modes for aid in achieving
compatibility with some competitive modems, especially in Turbo FEC modes. These modes are
denoted by the FEC Option “CT” on the front panel selection. These modes are typified by the
modes used in the CDM5xx and CDM6xx series of competitive modems.
There are several modes that are probably not compatible for several reasons. First is
that there is no standard for implementation of TPC. Second, Datum Systems spent a lot
of time and development in implementing a full set of TPC parameters (i.e. Rates 1/2, 3/4
and 7/8), and insuring the absolute best performance with no compromises. We have
seen no other TPC implementation that even comes close to ours. Third, because we
have many customers that use our modems in systems requiring low latency we
implemented an alternate "Short Block" mode that reduces the typical TPC delay by
approximately 1/3. The techniques used in this TPC achieve the best performance of any
modem currently produced. Our latest TPC “Advanced” modes are also proprietary to
Datum Systems, simply because we know of no one else using the specific parameters.
The PSM-500 has significant new capabilities and features that cannot fit into the structure of the
PSM-4900 protocol. However, the PSM-500 will respond to properly formatted PSM-4900 binary
control packets within the capabilities of the PSM-4900. This allows mixed systems of 4900 and
500 series modems without initially changing control software. The compatibility does not
currently extend to operation over the link on the MCC channel.
My PSM-500 and PSM-2100 do not agree on the Eb/No parameter with Reed-Solomon
Codec installed?
The PSM-2100 was designed before Intelsat IESS 309 added the section defining how the Eb/No
was measured with Reed-Solomon concatenated coding, and uses a different method. The
method is encapsulated in ASIC and not changeable. Unfortunately the IESS lists two possible
methods of computing the Eb/No with Reed-Solomon. The PSM-500, being of more recent
design, adheres to both IESS definitions by allowing the reference point to be varied. The two
therefore may read differently, but actually achieve the same performance. Refer to Appendix RS
for more information on setting the calculation parameter.
Does the PSM-500 have AUPC and AUFC and are they compatible with the PSM-2100?
The PSM-500 does not have AUFC, but retains the AUPC from the PSM-2100 type modems.
Like the PSM-2100 the built in AUPC (Automatic Uplink Power Control) can be enabled only if the
multiplexer option is installed or if an external communications channel is provided.
The PSM-500 AUPC is compatible with that in the 2100 when the PSM-500 modem IBS
Multiplexer is placed in the “Enhanced” mode. It is not compatible in the “Custom” mode.
How do I set up the IBS Multiplexer and AUPC Option in the PSM-500 to be compatible
with the PSM-2100 Modem?
The PSM-500 Modem is capable of varying the parameters for the IBS Multiplexer beyond the
capabilities of the PSM-2100. To maintain compatibility with the PSM-2100 specific similarly
named options are available in the PSM-500. These modes are the “Standard” and "Enhanced”
multiplexer operating modes. The 500’s “Custom” mode is not compatible with the PSM-2100.
For the AUPC to function and to be compatible with a PSM-2100 it must be set in the “Enhanced”
mode.
How do I set up the Reed-Solomon Option in the PSM-500 to be compatible with the PSM-
2100 Modem?
The PSM-500 Modem is capable of varying the parameters for the Reed-Solomon Codec beyond
the capabilities of the PSM-2100. To maintain compatibility with the PSM-2100 specific similarly
named options are available in the PSM-500. When enabled the RS FEC Mode should be set to
“IESS-308”. This will automatically set the “n”, “k” and “Depth” options to 126, 112 and 4
respectively. The 500’s “IESS-309” and “Custom” modes are not compatible with the PSM-2100.
The PSM-500 is highly programmable. This can make the set-up daunting at first. If you are
unfamiliar with the common terms and modes used in satellite communications you should first
refer to Chapter 2 of this manual “Installation and Setup”. As a starting point the modem can also
be taken to a default basic set of operating parameters by using the front panel <Unit:
Configuration - Recall> parameter and select option “0” or “Factory”. From that point you make
necessary changes to set the desired configuration. Once all parameters are set as required the
configuration can be saved using the <Unit: Configuration - Store> control. From there you can
always go back to this configuration by recalling it.
Why doesn’t my PSM-500 talk to another PSM-500 over the satellite? I have set all the
parameters the same.
Any satellite modem has a significant number of parameters, which are settable in order to
achieve the maximum performance at the least cost. Because there are so many parameters it is
possible to have one unit with a slightly different parameter set than that at the other end of the
link. If after insuring that all parameters are set the same and that the acquisition range is correct
and that there are no interfering carriers; one other method is to take both modems back to the
factory default condition and rebuild the configuration from “scratch”. Use the front panel <Unit:
Configuration - Recall> and select option “0” or “Factory”. You may want to save your current
configuration before resetting to the default.
What is the delay from end to end using the PSM-500?
The satellite link itself represents a fixed and very slightly variable delay due to the distance of the
satellite from the two stations linked. This delay is approximately 250 milli-seconds. In addition
Appendix A lists the specified fixed and rate dependent delays incurred in the modem’s transmit
and receive processing, including those in the IBS Multiplexer and Reed-Solomon if equipped
and enabled.
Can I use the PSM-500 to help align the station antenna?
Is an AGC output provided to feed to automatic antenna positioning equipment?
Yes - The PSM-500 has a single analog output that is produced by the main processor and
converted to analog by a D/A converter. The parameter selected for this output can be either the
AGC, Eb/No or Mod CXR Level selected in the <Unit: Monitor - Mode>. The slope and polarity
are selected using the “Zero” and “Full” parameters below this. The signal is available at the rear
panel on the J5 Alarm Connector, pin 5 with the Ground return on pin 6. See Installation Section
2.3.3, “Alarm Connection”, and Operations Section 3.11 for more information on connection and
use of the monitor function.
The AGC has been the classic parameter used for this type of function, but the PSM-500
provides an output that may be better in most situations. That is the Eb/No, which is a function
without the slope changes and negative signal sense of the AGC signal.
Where is the “Eye Pattern” test points for the I and Q channel receive signals?
The PSM-500 does not have an analog test point to view the eye pattern. All information at this
point in the receive chain is digital and measured by the modem processor. The result of this
measurement is presented as the Eb/No. If it is absolutely essential to view the eye pattern as
analog test information, contact the factory for availability of a special test fixture for conversion.
What happened to the Burst Modulator mode in the PSM-500?
The PSM-500 has the basic circuitry necessary to implement burst modulation. The burst
demodulation scheme compatible with the modulation used in the PSM-2100 is no longer
manufactured, and there is no clear standard for implementing this capability. Modifying the PSM-
500 to work with a specific burst demodulator scheme is an option which requires contacting the
factory for availability.
How do I use the modulator and demodulator functions to invert the spectrum?
These options were added into the PSM-500 to aid in building specialized systems which may
invert the spectrum sense of the received carrier. The main cause of this would be an up or down
converter which performs a spectrum inversion.
How do I use the modulator and demodulator functions to vary the FEC C0 and C1 values?
These options were added into the PSM-500 to help achieve compatibility with other brands of
modems at the other end of a link. These parameter settings also allow changing the modulation
of adjacent carriers on the satellite so that a demodulator will not lock to them. This has value if
the carriers are placed closer than the required receive acquisition range. Using this scheme
requires the use of the demodulator search mode.
Intelsat in the latest IESS 308/309 has changed the definition of the C0 and C1 values. This
option allows compatibility with any definition.
You probably have the differential encoder/decoder turned off. It is only provided as a control for
very special cases and should normally be set to “Enabled”.
The modem changed its operating parameters without me doing anything!
The ACR or Automatic Configuration Recovery feature is possibly enabled by setting one of the
<Unit: Config – Recall X> parameters set to a non-zero value. This will change the modem
configuration if the receive carrier is lost longer than the number of seconds entered.
The <Unit: Config – Power-Up> parameter may be set to change to a specified configuration on
power-up. The normal setting for this is “Last” (0).
In normal operation there is no need to disable the Differential encoder or decoder. We only
found that occasionally someone disabled it and then had problems locking up to carriers, so this
capability was initially removed from front panel control. All of the latest firmware however now
allows this control, so you may need to update your firmware.
How do I enter a number with a minus sign?
At any time during the “Edit” process the “+/-“ key will change the sign of the current entry (if the
change is possible). In the quick edit mode this can be the first key pressed, so for instance, if the
current setting for modulator transmit output level is –10 dBm then pressing “+/-, 12” will enter a
value of –12 dBm. You could also press “1+/-2” or “12+/-” with the same result.
Why doesn’t the PSM-500 front panel act like the PSM-2100 or PSM-4900? [and] How do I
make it act like the PSM-2100?
The PSM-500 has many more features and programmable options than the PSM-2100 modems.
A close match is achieved by disabling the “quick” entry mode and remembering to press the
“Edit” key first instead of the “Enter” key. Once you become accustomed to the “Quick” entry
mode and using the change sign (+/-) and decimal point keys you will find it more convenient
than any entry on the PSM-2100.
Why does the transmit carrier turn off whenever I make a change?
First the transmit carrier can be set to a mode which will turn the carrier off if any change is made
that would result in a possible interference with other carriers on the satellite. This mode can be
set to one of three states: Automatic, Confirm or Manual. Automatic will turn the carrier off during
the parameter change and return the carrier on (if currently enabled) after the change is
completed, Confirm will ask if the carrier should be left on (requiring a “yes” or “no” answer), while
Manual will always turn the carrier off after a change. This option is set in <Mod: IF – Mute>.
More directly the setting described is probably set to “Manual” mute mode.
Why can’t I find or see a certain option parameter that is shown in the tables?
Many parameters are only available when another option has been enabled which requires that
parameter. For example, the <Demod: IF – Sweep Time> parameter is only visible if the
<Demod: IF – Sweep Mode> is set to “Search”. These options are shown in the tables as gray
to indicate this status.
Can I control the far end modem from the front panel of a local modem?
The PSM-500 has the ability to control the far end modem (when linked and locked) from a local
modem, but only using the remote control port. This ability requires enabling the Multiplexer
option. Control from the front panel is prone to possible mistakes that would lead to accidentally
setting the remote modem in a state that could not be recovered without going to the remote site.
The far right “Remote” LED is blinking. What does it mean?
The Unit Remote Activity parameters allow setting this lamp to blink when activity is detected on
the USB or serial remote control ports. The same is possible for the “Local” LED using the Unit
Keyboard Activity control.
I seem to have no modulator or demodulator functions available?
There are two reasons that could explain this. First, there are some units sold with only one
function installed for special purposes. These units would have a model number indicating this
such as PST for a Modulator transmit only or PSD indicating a Demodulator receive only.
The other reason could be that the Modulator or Demodulator is disabled. To check and enable if
desired, go to the <Unit: Config – Modem>.parameter which shows what is enabled and allows
changing.
What do the abbreviations on the front panel and in the manual mean?
C. Remote Control
Where is the ASCII Control packet structure in the PSM-500?
The PSM-500 and the PSM-4900 modems do not have an ASCII control packet protocol, only the
binary packet protocol. The SnIP however does have a fairly complete command line driven
control method via the “m500ctl” program. In addition the SnIP can potentially control multiple
modems connected via its external RS-485 control port.
Can I use the USB connector at J10 to remotely control the PSM-500?
The USB connector is mainly intended for firmware updates requiring a faster speed than the RS-
232/449 connection can supply. It is possible to control the modem in binary packet mode via the
USB connection. However, this connection does not use or accept addresses in the packet
structure, so it will likely require re-writing your packet routines.
You cannot currently use the USB connection for “Terminal Mode” control.
Is there a “compatibility” mode for the remote control binary packet protocol that looks
like that in the PSM-4900?
Yes. The new PSM-500 design dictated a new structure to implement the significantly greater
number of commands available in the PSM-500. Many items such as the interface structure, data
rates and available options are so different that creating a compatible command set was
impossible. However the PSM-500 actually contains both its own and a copy of the PSM-4900
protocol, allowing the PSM-500 to accept and respond to PSM-4900 packets within the limitations
of the PSM-4900 capabilities. This allows mixed systems of 4900 and 500 series modems
without initially changing control software. The compatibility does not currently extend to
operation over the link on the MCC channel.
Is there a “compatibility” mode for the remote control binary packet protocol that looks
like that in the PSM-2100?
No. The new commands dictated a new structure to implement the significantly greater number of
commands available in the PSM-500. Many items such as the interface structure, data rates and
available options are so different that creating a compatible command set was impossible. The
packet structure itself is virtually identical though and in most cases the new command set can be
accommodated by a “driver” tailored to the PSM-500.
D. Data Interface
How do I make a cable to connect to my V.35 (or EIA-530) device?
See the “Installation” Chapter 2 and Appendix C on “Cabling Specifications” which shows how to
make cables to interface between the modem’s DB37 connector and other types of common
connectors used.
Where do I get a “Y” cable to implement 1:1 redundancy?
These may be purchased from Datum Systems or it is possible to build your own. The
connections are discussed in Chapter 2 “Installation” and shown in Appendix C, “Cabling
Specifications”.
Why do I keep getting “sync losses” on my link? Or why does a BERT test show “sync
losses”?
This is usually a sign that some section of the link has a clock or data inversion. See Chapter 4 of
the manual for “Loop” testing to try to determine where the problem is and correct either the
wiring or change the modem data or clock sense.
Why does the modem occasionally fail to operate with my DTE equipment, and to correct
it I have to invert the data or clock?
The only cause in an otherwise functioning modem for this symptom is that the differential
encoder/decoder is turned off. Modems use the differential encoding to determine the proper
relationship between the clock and data. If the encoder is turned off the modem has a possibility
of locking to a signal with the wrong phase. For all normal operation of the modem the Modulator
differential encoder and the Demodulator differential decoder must be “Enabled”.
The Turbo Product Codes (TPC) option does not use the differential encoder, and when it is
enabled the differential encoder and/or decoder is turned off and the option is removed from the
parameter matrix. Other modes also automatically control the differential encoder and decoder in
the PSM-500, but a linked modem may have the ability to turn it on or off.
How do I use the built-in Bit Error Rate Test (BERT) set?
See Maintenance Section 4.1.2 for information on using the built-in BERT. The PSM-500 BERT
now has the ability to be switched to look at the data line side.
Can I use the built-in Bit Error Rate Test (BERT) set to test the line or DTE side
equipment?
Yes with reservations. The BERT is designed to normally transmit and receive to the modem
side. New in the PSM-500 is the ability to electrically switch the direction that the BERT “looks”
toward the line side. However, because of the hard wiring of the interface the pinout is fixed as a
DCE device. See Maintenance Section 4.1.2 for information on using the built-in BERT.
Why doesn’t my 1:1 redundant switch on certain alarms?
The 1:1 redundancy logic is programmable on two levels. First is the <Unit: Redundcy – SW
Rqst> parameter which selects whether a switch is requested on all alarms, alarm A and/or
alarm B. If it is set to any options but “On All Alarms” then the particular alarms that are summed
into the A and B alarms are themselves programmable, creating the second level. See the
discussion in section for more information.
E. Manual
What do the abbreviations on the front panel and in the manual mean?
A good example is the display and manual representation "Redundcy SW Rqst". Unfortunately
the display does not hold enough characters to display the full text of "Redundancy Switch
Request". Following is a list of abbreviations used.