SU446019A1 - The method of measuring the irregularity of the group time delay in the frequency band - Google Patents

Description

one

The invention relates to a measurement technique and can be used to observe and control the group delay time (DTP) of various quadrupoles, in particular, communication lines.

There is a known method for measuring the non-uniformity of a group of orders in a frequency band by inputting a test signal to a quadrupole to the input and comparing the parameters of this signal with the parameters of the reference signal.

The disadvantages of this method are high error due to imperfection of modulation, due to instability of carrier purity, inconvenience of measurements associated with the oscillation of the frequency of the measuring generator and the need to transmit a reference signal when measuring in communication channels, the input and output of which are separated.

With an increase in the accuracy and automation of the measurement process, the input measurement signal is formed as a discrete set of frequencies uniformly overlapping the range under study, and by heterodyning, the ordinates of the frequency response of the group delay time are determined by the phase relations between the components of this set at the quadrupole output, and the reference signal is formed at the output of the quadrupole in the form of oscillations, the frequency of which is equal to the interval of a discrete set of frequencies.

The drawing shows a block diagram of a device explaining the proposed method.

The device comprises a low-frequency generator 1, a converter 2, a quadrupole 3 under study, an amplifier 4, a phase locked loop system 5, a mixer 6, a oscillating frequency generator 7, a band-pass filter 8, a phase metering device 9 and a phase shifter 10.

The method is as follows. The low frequency signal Q from oscillator 1 is fed to transducer 2, which is used to obtain a measurement signal in the form of a discrete set that covers the entire frequency range under study at Q interval. The measurement signal is fed to the input of the quadrupole under study 3. On

the output of the last measuring signal through the amplifier 4 is fed to the input of the phase locked loop system 5 and to the input of the mixer 6. The unmodulated signal is fed to the second input of the system 5 and the second input of the mixer

from oscillator 7. When oscillating, the oscillator frequency is captured for some time (using system 5) in turn by each component of a discrete set of frequencies. During the time that system 5 is running in

hold mode, a measurement is taken

for which, from the output of the mixer 6, the low intermediate frequency signal through the band-pass filter 8 is fed to the input of the phase measuring device 9, in which it is compared in phase with the reference signal of the generator 1 fed to the input of the phase measuring device through the phase shifter 10. During one swing The generator frequency 7 indicator produces N such comparisons, where A is the number of components of a discrete set of frequencies lying in the sweep range of the oscillator frequency generator 7.

The phase of the oscillation frequency O at the output of the band-pass filter is determined by the difference in phase incursions in the quadrupole under study, the two components of a discrete set of frequencies closest to the frequency of the trapped heterodyne.

This means that the indicated phase is proportional to the slope of the phase-response characteristic under study, i.e. the group delay time, in the section of the frequency axis between these components. By setting an appropriately fixed phase of the reference signal with the phase shifter 10, it is possible to eliminate the constant component of the delay group, so that the phase measuring device will only induce deviations of the delay group from a certain constant value.

To calibrate the measuring system, it is necessary to check the linearity of the phase relationships between the components of a discrete set of frequencies at the output of converter 2. If the linearity is broken, then the zero line must be registered separately when converter 2 is connected directly to divider 4 and used in further measurements for corrections.

The main difference of the invention is in the formation of a measuring signal, which excludes the use of a sweeping frequency generator at the input of the measuring system. This reduces measurement errors caused by instability and frequency uncertainty of the input signal, since the frequency stability of the components of a discrete set of frequencies can be made very high, and also simplifies the maintenance of the measuring system and, ultimately, increases the degree of automation of the measurements.

When measuring, it is necessary to provide a sufficiently low level of the measuring signal at the mixer output. Otherwise, the beat between each pair of adjacent components of a discrete set of frequencies will introduce an error into the phase of the intermediate frequency signal. The intermediate frequency at the input of the phase measuring device may

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be installed any. For this, the frequency of the local oscillator should not be captured directly at the frequency of the components of the discrete set of frequencies, but at some distance 5 from it equal to the frequency of the reference signal of the phase-locked loop system. In this case, the difference between the local oscillator frequency and another component of a discrete set of frequencies is singled out as an intermediate frequency. Thus, the operating frequency for the indicator is the difference between the base frequency Q and the frequency of the reference signal. The reference signal of this frequency is obtained by highlighting the difference between the reference base

5 by the frequency Q and the frequency of the reference signal of the phase locked loop system.

With such a construction of the measuring system, strict requirements to the level of the measuring signal are eliminated, since parasitic combinations equal to the intermediate frequency are not present in the signal spectrum at the mixer output.

The reference frequency can be transmitted in the usual way.

5 (pilot signal, cable line, etc.).

The advantage of this method of measurement is the ability not to transmit the reference signal at all, but to form it on the quadrupole output by detecting the measuring signal. The components of a discrete set of frequencies arriving at the detector form a whole series of combination frequencies, the lowest of which, equal to the base frequency Q, can be easily identified using

filter; the frequency of the nearest unwanted component is 2Q.

Subject invention

A method for measuring the group time non-uniformity of a delay in a frequency band by inputting a quadrupole measurement signal to the input and comparing

the parameters of this signal with the parameters of the reference signal, characterized in that, in order to increase the accuracy and automation of the measurement process, the input measurement signal is formed as a discrete set of frequencies uniformly overlapping the range under study, and the heterodynamics determine the ordinates of the frequency characteristic of the group time delay by phase relations between

components of this set at the output of the quadrupole, and the reference signal is formed at the output of the quadrupole in the form of oscillations whose frequency is equal to the interval of a discrete set of frequencies.