SU811501A1 - Device for measuring inhomogeneity of frequency characteristics of communication chennel - Google Patents

Description

additional mixer and low pass filter.

FIG. 1 shows the structural electrical circuit of the device; in fig. 2 is a structural electrical circuit of a modulator and an additional modulator.

A device for measuring the unevenness of the phase-frequency characteristic of a communication channel includes a carrier frequency generator 1, a modulator 2, an amplifier 3, a mixer 4, a narrowband filter 5, a phase detector 6, a phase shifter 7, a discrete frequency generator 8, a reference signal conditioner 9 blocks 10 and 11 of the phase-locked loop (PLL), an additional generator 12 of the carrier frequency, a modulator 13, a mixer 14, a narrow-band filter 15, in addition, the modulator 2 and the additional modulator 13 contain a generator of 16 square impulses The second, additional narrowband filter 17, the second additional mixer 18 and the frequency filter (LPF) 19.

The device works as follows.

The signal carrier frequency from the output of the generator 1 is fed to the input of the mixer 18 of the modulator 2, to the other input of the mixer 18 from the output of the narrow-band filter 17 receives pulses of the form sin x / d :. A coBiviecTHO rectangular pulse generator 16 with a narrowband filter 17 serves to generate sin xjx modulating pulses.

At the output of the low-pass filter 19 of the modulator 2, an amplitude-mol is obtained, a verification signal (AM), the envelope of which is changed by the law sin xjx. The formation of the AM signal of the sin xlx type of signal allowed us to obtain a signal whose spectrum is discrete and all its harmonic components have the same amplitudes and initial phases. The AM signal thus generated from the output of the low-pass filter 19 of the modulator 2 is fed to the input of the measured communication channel 20.

Due to the non-linearity of the channel's frequency response, the AM signal transmitted through the measured communication channel 20 is distorted, and each harmonic component in the AM spectrum of the signal will receive an additional phase shift introduced by the channel at a given frequency. The AM signal from the output of communication channel 20 is fed to the input of amplifier 3, from the output of which the signal is fed to the input of mixer 4 and to the inputs of blocks 10 and 11 of the PLL.

The second input of the mixer 4 receives a signal from the output of the generator 5 discrete frequencies. At each discrete time from the generator 8 discrete frequencies to the input of the mixer 4 receives a signal with frequency / i.

At the output of the mixer 4 a narrow-band filter 5 extracts the signal with an intermediate frequency / o, i.e. / o / n - / g, where fn is the harmonic component

AM signal.

Thus, each harmonic component of the AM signal, which is not received from the output of communication channel 20, is extracted.

The output of the narrowband filter 5 at the frequency / o is fed to the input of the phase detector 6, to another input of which a reference signal is output from the output of the reference signal generator 9 through the phase shifter 7. There is a generator -12 and -modulator 13 for generating the reference signal of the reference signal generator 9. , similar in their characteristics to the corresponding devices on the transmission. At the output of the modulator 13, a reference AM signal is formed with an envelope of the form sin.

The // PLL unit eliminates the phase difference between the AM reference signal and the AM signal that comes from the output of the measured communication channel 20. The use of the // PLL unit allowed us not to take into account the linear component of the frequency response of the communication channel.

PLL unit 10 makes trimming

frequencies of the carrier oscillation generated by the generator 12 of the driver 9 of the reference signal, under the carrier AM signal received from the output of the communication channel 20. The use of block 10 PLL iosvolil to eliminate the phase difference of the carrier oscillations generated by the generators 1 to 12 on the transmitting and receiving sides, caused by the temporary instability of the frequencies of these generators. The reference AM signal formed at the output of the modulator 13 of the driver 9 of the reference signal will differ from the AM signal from the output of communication channel 20 only by distortions in the latter caused by irregularity of the frequency response of communication channel 20.

In order to isolate the p-th harmonic component from the spectrum of the AM reference signal, this signal from the output of the modulator 13 is fed to the mixer 14 of the driver

9 reference signal to the other input of the mixer 14 receives a signal from the generator output 8 dskretnyh frequencies. The narrow frequency filter 15 of the driver of the reference signal 9 is allocated intermediate frequency

/ 0 from the output of the reference signal generator 9 enters the input of the phase shifter 7. The output signal of the phase shifter 7 receives the reference signal at the second input of the phase detector 6. The output of the phase detector 6 generates a signal proportional to the phase difference of the nth harmonics of the reference and measuring AM signals .

By varying the frequency of the generator of 8 discrete frequencies, the remaining harmonic components are extracted from

AM reference and measurement spectra. Thus, at the output of the phase detector 6, signals will appear corresponding to the non-uniformity of the phase response of the measured channel 20 cor.

Such a connection of the nodes will allow receiving and transmitting a discrete set of frequencies with the same initial phases, which will increase accuracy and shorten the measurement time due to the lack of calibration, and will also allow you to simply generate a reference signal at the receiving point.

By varying the frequency of generators 1 and 12 on the transmission and reception, the proposed device is easily tuned for any frequency range, and by changing the pulse duration at the generator output of 16 square-wave pulses, you can change the number of discrete components in the AM spectrum.

Claims (3)

1. A device for measuring the unevenness of the phase-frequency characteristic of a communication channel, containing in the transmitting part serially connected carrier frequency generator and modulator, and in the receiving part - serially connected amplifier, mixer, narrowband filter and phase detector, the second input of which is connected to the output of the phase shifter, characterized in that, in order to increase accuracy while reducing the measurement time, discrete frequencies and forms connected in series are introduced in the receiving part The reference generator, while the output of the amplifier is connected to the second input of the driver of the reference signal, the first input and output of which are connected respectively to the second input of the mixer and to the input of the phase shifter. 2. The device according to claim 1, otlnchayusche the fact that the shaper of the reference signal is made in the form of serially connected to the first block of the phase-locked loop, the first input of which combined with the first input of the second phase locked loop, an additional carrier frequency generator, an additional modulator, an additional mixer, and an additional narrowband the filter whose output is the output of the signal conditioner, the first and second inputs of which are respectively the second input of the additional mixer and the combined first inputs the first and second blocks of phase-locked loop, the second inputs of which are connected respectively to the second outputs of the auxiliary carrier frequency generator and the auxiliary modulator, the second the input of which is connected to the output of the second phase locked loop unit. 3. The device according to PP. 1 and 2, that is, so that the modulator and the additional modulator are each in the form rectangular pulse generator, a second additional narrowband filter, a second additional mixer and a low pass filter. 35 The source of information taken into account in the examination: 1. USSR author's certificate No. 446019, cl. G 04 F 10/06, 1972 (prototype). ig.2