GB2404294A

GB2404294A - Adapter for converting a DAB broadcast signal to an analogue radio signal

Info

Publication number: GB2404294A
Application number: GB0317436A
Authority: GB
Inventors: Matthew Forbes Bramble
Original assignee: Audio Partnership PLC
Current assignee: Audio Partnership PLC
Priority date: 2003-07-25
Filing date: 2003-07-25
Publication date: 2005-01-26
Also published as: GB0317436D0

Abstract

A signal adapter 10 comprises an input 12 for receiving a Digital Audio Broadcast (DAB) signal and a converter for converting the DAB signal to an analogue radio frequency signal. The output signal may lie in the MF or VHF radio bands. The adapter may be configured to extract text or data from the DAB signal and may include an encoder to convert at least some of this data to radio data system (RDS) data in the output signal. The adapter may also receive a digital data stream from a computer network, for example an Internet radio signal, and convert this to an analogue radio signal.

Description

TITLE: CONVERSION OF A BROADCAST SIGNAL TO AN ANALOGUE

RADIO FREQUENCY SIGNAL

DESCRIPTION

The present invention relates to conversion of a broadcast digital audio signal to an analogue radio frequency signal.

Digital Audio Broadcasting (DAB) is becoming more widely used and offers advantages over analogue audio broadcasting, such as FM and AM broadcasting. Advantages include improved reception, improved clarity of sound and greater radio station choice. However, the rate at which DAB radio is being adopted by listeners has not met expectations. DAB radio receivers are, on the whole, more expensive than their analogue counterparts. Moreover, many people feel that the advantages of DAB are not sufficient to justify replacement of their existing analogue receivers.

An aim of this invention is to enable radio listeners to access DAB broadcasts more readily and perhaps also at a lower cost than has previously been possible.

Awareness of developments in digital audio broadcasting and of the expense of DAB radio receivers has, amongst other factors, led the applicant to devise the present invention.

According to a first aspect of the present invention there is provided a signal adapter comprising an input for receiving a first signal comprising a Digital Audio Broadcast signal and a converter for converting the Digital Audio Broadcast signal to a second signal comprising an analogue radio frequency signal, which, in use, is made available at an output of the signal adapter.

The output may include a connector suitable for connection to an antenna input of a radio receiver.

Alternatively or additionally, (bearing local regulations in mind) the output may include radiating means for radiating the second signal.

The signal adapter may be used in conjunction with a conventional analogue radio receiver (e.g. an FM radio or FM tuner). In use, the signal adapter may be positioned, perhaps next to the conventional analogue radio receiver, with the input of the signal adapter connected to a Digital Audio Broadcast (DAB) aerial. The output of the signal adapter may be connected to a radio frequency input of the conventional analogue radio receiver or the analogue radio receiver may be placed within range of the radiated second signal, as the case may be. Thus, a user can receive DAB broadcasts whilst continuing to make use of his conventional analogue radio receiver.

The invention can in certain circumstances provide a user with a more cost-effective way to receive DAB broadcasts than discarding his conventional analogue radio receiver and replacing it with a combined analogue/DAB radio receiver. In other circumstances, the invention may provide for DAB radio reception where installation of a combined analogue/DAB radio receiver may not be readily accomplished.

For example, a car owner may only be able to up-grade an existing analogue radio receiver by replacing an entire factory-fitted audio system; perhaps he might even find it difficult or impossible to remove the factory-fitted system.

Perhaps no DAB receiver is available that will fit the form- factor available in his car. At any rate, the invention may address a user's reluctance - for whatever reason - to change his pre-existing apparatus, where such a change involves, for example, adding a further unit to or replacing an existing unit of his hi-fi system.

The converter may be configured to decode the Digital Audio Broadcast signal as an analogue audio signal, perhaps as a base-band audio signal.

The signal adapter may comprise a frequency generator for generating a carrier wave and a modulator for modulating the carrier wave with the analogue audio signal in accordance with a modulation method. The modulation method may, for example, be FM or AM.

The carrier wave may have a frequency between substantially 535 x 103 Hz and 1605 x 103 Hz, i.e. in the medium frequency band. In such a frequency band, the modulation method will normally be AM.

The carrier wave may have a frequency between substantially 88 x 106 Hz and 108 x 106 Hz, i.e. in the VHF band. In such a frequency band, the modulation method will normally be FM.

The frequency generator may be adjustable, perhaps by a user of the signal adapter, to generate a carrier wave of variable frequency. Thus, a carrier wave frequency may be selected to minimise interference from other signals, such as radio frequency broadcast signals. In addition, the carrier wave may be set at a predetermined frequency that matches a predetermined frequency on a conventional analogue radio receiver. For example, the predetermined frequency on the conventional analogue radio receiver might be a pre-set channel.

The signal adapter may further comprise another input for receiving a third signal comprising an analogue radio frequency signal, the third signal being of the same form (e.g. FM) as the second signal and the signal adapter being configured to convey the third signal to the output. Thus, a user of the signal adapter may be able to receive first and second signals (i.e. a DAB signal and, for example, an FM signal) and to change between them without modifying the signal adapter or his conventional analogue radio receiver.

A DAB signal typically comprises digital text and/or control data in addition to a digital audio signal. Thus, the signal adapter may be configured to extract text and/or control data from the DAB signal, and the signal adapter may further comprise an encoder for encoding at least some of the extracted text and/or control data as digitally encoded data, and a combining device for combining the digitally encoded data with the second signal.

The combining device may be operative to modulate a carrier wave with the digitally encoded data.

More specifically, the combining device may comprise a sub-carrier modulator for modulating a sub-carrier with the digitally encoded data, and the signal adapter may be configured to modulate the carrier wave with the modulated sub-carrier.

The sub-carrier modulator may be operative according to a phase modulation method, perhaps Quadrature Phase Shift Keying (QPSK).

The digitally encoded data may be in a radio data system (RDS) format.

The signal adapter may advantageously be constructed as a stand-alone apparatus. For example, it may take the form of a consumer product. Such apparatus can be used with a pre-existing analogue radio receiver without modification to the receiver. Moreover, such embodiments can be constructed so that their installation requires little technical skill or knowledge.

According to a second aspect, there is provided a method of converting a DAB signal to an analogue radio frequency signal, the method comprising the steps of receiving at an input a first signal comprising a Digital Audio Broadcast signal, converting the Digital Audio Broadcast signal to a second signal comprising an analogue radio frequency signal and making the second signal available at an output. Such a method is typically performed in apparatus embodying the first aspect of the invention.

Having arrived at this invention, the applicant realised that it has broader application than has been described above. There are further broadcast signals that may be converted to an analogue radio frequency signal for input to a conventional analogue radio receiver.

Therefore, from a third aspect there is provided receiving apparatus comprising an input for receiving a digital data stream from a computer network and a converter for converting the digital data stream to a second signal comprising an analogue radio frequency signal, which, in use, is made available at an output of the receiving apparatus.

The computer network may be the Internet. In such embodiments, the input may include apparatus that can connect to the Internet over a telephone network, examples being an analogue modem, a DSL or cable modem or an ISDN terminal adapter. Alternatively, the input may include an interface to a local area network that can route data to and from the Internet, examples being a hard wired network interface, or a wireless network interface for instance in accordance with IEEE 802.11 or Bluetooth (r.t.m. ).

The digital data stream may comprise an Internet radio signal.

The receiving apparatus may be used in conjunction with a conventional analogue radio receiver. Thus, a user can receive digital data stream broadcasts from the Internet whilst continuing to make use of his conventional analogue radio receiver. Application of the present invention in accordance with the third aspect may indeed seem counter intuitive.

Receiving apparatus embodying this aspect of the invention may operate in a stand-alone manner. For example, it may be a consumer electronics product that need only be connected to the network and be provided with a source of power in order to work. This enable a user to listen to Internet streams without the need to use a computer.

Alternatively, receiving apparatus embodying this aspect of the invention may be embodied within a card or a peripheral device for a computer, wherein the input is connected to a bus of the computer. Such embodiments can make use of a pre-existing Internet connection.

The converter may be configured to decode the digital data stream as an analogue audio signal, perhaps as a base- band signal.

The receiving apparatus may comprise a frequency generator for generating a carrier wave and a modulator for modulating the carrier wave with the analogue audio signal i in accordance with a modulation method. The modulation method may, for example, be FM or AM.

The frequency generator may be adjustable, perhaps by a user of the receiving apparatus, to generate a carrier wave of variable frequency. Thus, a carrier wave frequency may be selected to minimise interference from other signals, such as radio frequency broadcast signals. In addition, the carrier wave may be set at a predetermined frequency that matches a predetermined frequency on a conventional analogue radio receiver. For example, the predetermined frequency on the conventional analogue radio receiver might be a pre-set channel.

The receiving apparatus may further comprise another input for receiving a third signal comprising an analogue radio frequency signal, the third signal being of the same form (e.g. FM) as the second signal and the receiving apparatus being configured to convey the third signal to the output. Thus, a user of the receiving apparatus may be able to receive the digital data stream and the second signal (i.e. an interned radio signal and, for example, an FM signal) and to change between them without modifying the receiving apparatus or his conventional analogue radio receiver.

According to a fourth aspect, there is provided a method of converting a digital data stream to an analogue radio frequency signal, the method comprising the steps of receiving at an input a digital data stream from a computer network, converting the digital data stream to a second signal comprising an analogue radio frequency signal and making the second signal available at an output. Such a method is typically performed in apparatus embodying the third aspect of the invention.

According to a fifth aspect of the present invention, there is provided a digital radio reception device comprising a signal adapter according to the first aspect of the present invention and a receiving apparatus according to the third aspect of the present invention.

The digital radio reception device may have user operable controls, such as a selector for selecting one or other of DAB signal reception and digital data stream reception. Alternatively or in addition, control may be effected by remote control, such as by infrared or radio frequency remote control, etc. Such a digital radio reception device may provide for diversity of broadcast signal reception.

Specific embodiments of the present invention will now be described, by way of example, and with reference to the accompanying drawings in which: Figure 1 is block diagram representation of a first embodiment of the present invention; Figure 2 is a flow chart representation of a first method embodying the present invention; Figure 3 is block diagram representation of a second embodiment of the present invention; and Figure 4 is a flow chart representation of a second method embodying the present invention.

With reference to Figure 1, a first apparatus embodying the present invention is embodied as a stand- alone signal adapter 10. The signal adapter 10 comprises a DAB signal input 12 for receiving a first signal comprising a Digital Audio Broadcast (DAB) signal, a DAB tuner 14, an FM modulator 16 with a variable frequency generator 18, and an output 20. Together the DAB tuner 14 and the FM modulator 16 constitute a converter for converting the DAB signal to an analogue radio frequency signal. In addition, the signal adapter 10 comprises an RDS encoder 22, a sub-carrier modulator 24, a sub- carrier frequency generator 26, and a base-band mixer 27. The signal adapter 10 also comprises an FM signal input 28 and a radio frequency (RF) mixer 30. Control of and user interface with the signal adapter are provided by a microprocessor 32, user controls 34 and an infrared (JR) receiver 36. The IR receiver 36 may be integral with the signal adapter 10. Alternatively, the IR receiver 36 may be separate from the signal adapter 10 and connected, for example, by means of a cable. Thus, the signal adapter 10 may be hidden from view, e.g. behind the pre-existing radio apparatus, and the IR receiver 36 positioned within line of sight of an IR remote control transmitter. A display 38 may be provided if it is desired to display information, e.g. relating to signal adapter set-up and operation, on the signal adapter 10. Alternatively or in addition, information may be sent for display on pre existing radio apparatus, as described below.

In use, the signal adapter 10 is positioned next to a pre-existing analogue radio receiver. The DAB signal input 12 is connected to a DAB aerial 40, the FM signal input 28 is connected to an FM aerial 42 and the output 20 is connected to an RF input 44 of the pre-existing analogue radio receiver. The connections might be made, for example, by means of co-axial cables. Alternatively, the DAB aerial and/or the FM aerial may be integral with the signal adapter 10. Possibly a single aerial or single aerial connection may be used to receive both DAB and FM signals.

In operation and with reference the method 50 shown in Figure 2, a DAB signal is received at the DAB signal input 12, 52 and is decoded by the DAB tuner 14 as an analogue base-band audio signal, which is input to the base-band mixer 27. The DAB tuner 14 also extracts text and control data from the DAB signal, which is subsequently encoded by the RDS encoder 22 in accordance with the radio data system (RDS) format. Encoding may involve translating the text or control data to its corresponding RDS code equivalent, for example, by means of a look-up table. Typically, the DAB standard supports a greater number of control codes than the RDS standard and thus some of the control codes extracted by the tuner 14 may not be encoded by the RDS encoder 22. A sub- carrier generated by the sub-carrier frequency generator 26 is modulated by the RDS encoded data in the sub-carrier modulator 24, and the base-band mixer 27 combines the resulting signal with the analogue base-band audio signal.

In the FM modulator 16, the combined analogue base-band audio signal and RDS modulated sub-carrier modulate a carrier wave in accordance with an FM method. (The decoding operation performed by the DAB tuner 14 and the modulation performed by the FM modulator together constitute the step 54 of converting the DAB signal to a second signal comprising an analogue RF signal.) The carrier wave is generated by the variable frequency generator 16 and is in the VHF band. The resulting FM signal is made available via the RF mixer 30 at the output 20, 56 and thereafter sent to the RF input 44 of the pre- existing analogue radio receiver. RDS information (such as a currently selected DAB station name) contained in the FM signal received by the pre- existing analogue radio receiver may be displayed, in the conventional manner, on a display provided on the pre-existing analogue radio receiver. The pre-existing analogue radio receiver display may also be used to display information relating to the set-up and operation of the signal adapter. Thus, if it is desired, the display 38 on the signal adapter 10 may be dispensed with.

The signal adapter is also be operative to receive an FM signal at the FM signal input 28 and to feed the FM signal to the RF mixer 30, where it is mixed with the DAB converted FM signal and made available at the output 20.

Thus, a user of the signal adapter 10 is able to receive and change between the DAB signal and the FM signal without modifying the signal adapter or the pre-existing analogue radio receiver.

The variable frequency generator 18 may be adjusted, by the user e.g. by means of the user controls 34, to generate a carrier wave of variable frequency. Thus, a carrier wave can be selected to minimise interference from other signals, e.g. radio frequency broadcast signals. In addition, the output of the variable frequency generator 18 can be set at a pre-determined frequency by the user to match a pre- set channel on his pre-existing analogue radio receiver.

User control of the signal adapter 10 can be exercised by means of the user controls 34 and/or the IR receiver.

Control functions include those discussed above (e.g. the control of the variable frequency generator 18) and also others, such as DAB channel selection. The display 38 may typically be used to display status information, such as the current DAB channel selected, etc. With reference to Figure 3, a second apparatus embodying the present invention is embodied as a receiving apparatus 60. The receiving apparatus 60 has certain components in common with the signal adapter 10 of Figure 1 and the same reference numerals are used where appropriate. Thus, reference should also be made to the description of the signal adapter of Figure 1. Referring to Figure 3, the receiving apparatus comprises a computer network signal input 62 for receiving an Internet radio signal (which constitutes a digital data stream from a computer network), a cable modem 64 and a converter 66.

All other components of the receiving apparatus are the same as those of the signal adapter of Figure 1.

In use, the receiving apparatus 60 is positioned next to a pre-existing analogue radio receiver. The computer network signal input 62 is connected to a computer network 68, e.g. by means of a data cable. The FM signal input 28 is connected to an FM aerial 42 and the output 20 is connected to an RF input 44 of the pre-existing analogue radio receiver, e.g. by means of co-axial cables.

In operation and with reference to the method 70 shown in Figure 4, an Internet radio signal is received at the input 72 and is provided by the cable modem 64 to the converter, which converts the Internet radio signal to an analogue base-band audio signal 74. The analogue base- band audio signal is used to modulate a wave carrier, as described above with reference to Figure 1, and the resulting analogue radio frequency signal made available at the output 20, 76. In all other respects, the operation of the receiving apparatus is the same as the signal adapter described above.

It is to be appreciated that the apparatus, methods and other features described with reference to the embodiments discussed above can be combined in other embodiments of the present invention.

Claims

CLAIMS: 1. A signal adapter comprising an input for receiving a first

signal comprising a Digital Audio Broadcast signal and a converter for converting the Digital Audio Broadcast signal to a second signal comprising an analogue radio frequency signal, which, in use, is made available at an output of the signal adapter.
2. A signal adapter according to claim 1, in which the output includes a connector suitable for connection to an antenna input of a radio receiver.
3. A signal adapter according to claim 1 or claim 2, in which the output includes radiating means for radiating the second signal.
4. A signal adapter according to any preceding claim, in which the converter is configured to decode the Digital Audio Broadcast signal as an analogue audio signal.
5. A signal adapter according to claim 4, in which the analogue audio signal comprises a base-band audio signal.
6. A signal adapter according to claim 4 or 5, in which the signal adapter comprises a frequency generator for generating a carrier wave and a modulator for modulating the carrier wave with the analogue audio signal in accordance with a modulation method.
7. A signal adapter according to claim 6, in which the modulation method is FM or AM.
8. A signal adapter according to claim 6 or 7, in which the carrier wave has a frequency between substantially 535 x 103 Hz and 1605 x 103 HZ, i.e. in the medium frequency band.
9. A signal adapter according to claim 6 or 7, in which the carrier wave has a frequency between substantially 88 x 106 Hz and 108 x 106 Hz, i. e. in the VHF band.
10. A signal adapter according to any of claims 6 to 9, in which the frequency generator is adjustable to generate a carrier wave of variable frequency.
11. A signal adapter according to claim 10, in which the carrier wave is gettable at a predetermined frequency that matches a predetermined frequency on a conventional analogue radio receiver.
12. A signal adapter according to any preceding claim, in which the signal adapter further comprises another input for receiving a third signal comprising an analogue radio frequency signal, the third signal being of the same form as the second signal and the signal adapter being configured to convey the third signal to the output.
13. A signal adapter according to any preceding claim, in which the signal adapter is configured to extract text and/or control data from the DAB signal, and the signal adapter further comprises an encoder for encoding at least some of the extracted text and/or control data as digitally encoded data, and a combining device for combining the digitally encoded data with the second signal.
14. A signal adapter according to claim 13, in which the combining device is operative to modulate a carrier wave with the digitally encoded data.
15. A signal adapter according to claim 14, in which the combining device comprises a sub-carrier modulator for modulating a sub-carrier with the digitally encoded data, and the signal adapter is configured to modulate the carrier wave with the modulated sub-carrier.
16. A signal adapter according to claim 15, in which the sub-carrier modulator is operative according to a phase modulation method.
17. A signal adapter according to any of claims 13 to 15, in which the digitally encoded data is in a radio data system (RDS) format.
18. A signal adapter according to any preceding claim, in which the signal adapter is constructed as a stand-alone apparatus.
19. A method of converting a DAB signal to an analogue radio frequency signal, the method comprising the steps of: receiving at an input a first signal comprising a Digital Audio Broadcast signal, converting the Digital Audio Broadcast signal to a second signal comprising an analogue radio frequency signal and making the second signal available at an output.
20. A method according to claim 19 performed in a signal adapter according to any of claims 1 to 18.
21. Receiving apparatus comprising an input for receiving a digital data stream from a computer network and a converter for converting the digital data stream to a second signal comprising an analogue radio frequency signal, which, in use, is made available at an output of the receiving apparatus.
22. Receiving apparatus according to claim 21, in which the computer network is the Internet.
23. Receiving apparatus according to claim 21 or 22, in which the input includes apparatus connectable to the Internet over a telephone network.
24. Receiving apparatus according to claim 21 or 22, in which the input includes an interface to a local area network that can route data to and from the Internet.
25. Receiving apparatus according to any of claims 21 to 24, in which the digital data stream comprises an Internet radio signal.
26. Receiving apparatus according to any of claims 21 to configured for operation in a stand-alone manner.
27. A card or a peripheral device for a computer comprising the receiving apparatus according to any of claims 21 to 25, in which the input is connected to a bus of the computer.
28. Receiving apparatus according to any of claims 21 to 26, in which the converter is configured to decode the digital data stream as an analogue audio signal.
29. Receiving apparatus according to claim 28, in which the analogue audio signal comprises a base-band audio signal.
30. Receiving apparatus according to any of claims 21 to 26, 28 and 29, further comprising a frequency generator for generating a carrier wave and a modulator for modulating the carrier wave with the analogue audio signal in accordance with a modulation method.
31. Receiving apparatus according to claim 30, in which the modulation method is FM or AM.
32. Receiving apparatus according to claim 30 or 31, in which the carrier wave has a frequency between substantially 535 x 103 Hz and 1605 x 103 Hz, i.e. in the medium frequency band.
33. Receiving apparatus according to claim 30 or 31, in which the carrier wave has a frequency between substantially 88 x 106 Hz and 108 x 106 Hz, i.e. in the VHF band.
34. Receiving apparatus according to any of claims 30 to 33, in which the frequency generator is adjustable to generate a carrier wave of variable frequency.
35. Receiving apparatus according to any of claims 30 to 34, in which the carrier wave is gettable at a predetermined frequency that matches a predetermined frequency on a conventional analogue radio receiver.
36. Receiving apparatus according to any of claims 30 to 35, in which the receiving apparatus further comprises another input for receiving a third signal comprising an analogue radio frequency signal, the third signal being of the same form as the second signal and the receiving apparatus being configured to convey the third signal to the output.
37. A method of converting a digital data stream to an analogue radio frequency signal, the method comprising the steps of receiving at an input a digital data stream from a computer network, converting the digital data stream to a second signal comprising an analogue radio frequency signal and making the second signal available at an output.
38. A method according to claim 37 performed in receiving apparatus according to any of claims 21 to 26 and 28 and 36.
39. A digital radio reception device comprising a signal adapter according to any of claims 1 to 18 and a receiving apparatus according to any of claims 21 to 26 and 28 and 36.
40. A digital radio reception device according to claim 39 having a user operable control for selecting one or other of DAB signal reception and digital data stream reception.
41. A signal adapter substantially as described herein with reference to the accompanying drawings.
42. A method of converting a DAB signal to an analogue radio frequency signal substantially as described herein with reference to the accompanying drawings.
43. Receiving apparatus substantially as described herein with reference to the accompanying drawings.
44. A method of converting a digital data stream to an analogue radio frequency signal substantially as described herein with reference to the accompanying drawings.