SU1705759A1 - Device for measuring mean rate of variation of frequency and modulation characteristic linearity of frequency-modulated generators - Google Patents

Abstract

The invention relates to radio engineering, in particular to radio measuring equipment. and can be used to measure the rate of change of frequency and the linearity of the modulation characteristics of frequency-modulated oscillators. The purpose of the invention is to increase the sensitivity and accuracy of measurement. The goal is achieved by multiplying the frequency deviation by m times and the intrapulse frequency deviations from the linear law of the input linear-frequency-modulated signal using a frequency converter. For this purpose, a phase modulator 24 is introduced into the device. Two mixers of frequency 5, 14, three band-pass filters 23, 1, 6, generator 25 and input amplifier 29. 3 sludge.

Description

FI.4

The invention relates to a radio metering technique and can be used to measure the rate of change of frequency and the linearity of the modulation characteristics of frequency modulated oscillators.

The purpose of the invention is to increase the sensitivity and accuracy of measurement.

To achieve the goal, a second band-pass filter 1, a third mixer 5, a third band-pass filter 6, a second mixer 14, a first band-pass filter 23, are introduced into the device for measuring the average rate of change of frequency and linearity of the modulation characteristics of frequency-modulated oscillators phase modulator 24, generator 25 and input amplifier 29. The device also contains the first mixer 2, the intermediate frequency amplifier 3, the first delay line 4, the frequency detector 7, the strobe stage 8, the frequency memory unit 9, the first phase shifter 10, counts 11, summing amplifier 12, phase shifter 13 to nil, second phase shifter 15. controlled oscillator 16, second integrator 17, first phase detector 18, second phase detector 19, second delay line 20, electron-counting frequency meter 21, subtracting unit 22 , amplitude detector 26, pulse shaper 27, video amplifier 28, oscilloscope 30, first integrator 31.

The invention relates to radio metering technology and can be used to measure the rate of change of frequency and the linearity of the modulation characteristics of frequency modulated oscillators.

The purpose of the invention is to increase the sensitivity and accuracy of measurement.

FIG. 1 shows a block diagram of an apparatus for measuring the average rate of change of frequency and the linearity of the modulation characteristics of frequency modulated oscillators; in fig. 2 and 3 are diagrams explaining the operation of the device.

A device for measuring the average rate of change of frequency and linearity of the modulation characteristics of frequency-modulated oscillators contains a band-pass filter 1, a mixer 2, an intermediate frequency amplifier 3, a delay line 4, a mixer 5, a band-pass filter 6, a frequency detector 7, a strobe cascade 8, block 9 frequency memory, phase shifter 10, counter 11, summing amplifier 12, phase shifter 13 per / 2, mixer 14, phase shifter 15, controlled oscillator 16. integrator 17.

phase detector 18, phase detector 19, delay line 20, electron-counting frequency meter 21, subtraction unit 22, band-pass filter 23, phase modulator 24, generator 25, amplitude detector 26, pulse shaper 27, video amplifier 28, input amplifier 29, oscilloscope 30, integrator 31.

Generator 25, phase modulator 24, band-pass filter 23, delay line 20, mixer 5, band-pass filter 6, mixer 1, intermediate frequency amplifier 3, strobe stage 8, frequency memory unit 9, phase detector 18, subtraction unit 22. video amplifier 28, integrator 31, oscilloscope 30 are connected in series, the synchronization input of the oscilloscope 30 and the synchronization input of the strobe stage 8 are connected to the output of the pulse former 27, the input of which is connected to the output of the amplitude detector 26. The output of the intermediate frequency amplifier 3 is connected to the input of 100 meter detector 7 and through the delay line 4 to the second input of the phase detector 18 and to the input of the phase detector 19, the output of which is connected to the second input of the subtractive unit 22. Frequency detector 7, summing amplifier 12, integrator 17, controlled oscillator 16, counter 11, a phase shifter 15, a mixer 14, a bandpass filter 1 are connected in series, the output of the bandpass filter 1 is connected to the second input of the mixer 2. The output of the generator 25 is connected to the first inputs of the phase shifter 15 and the phase shifter 10, the second input of which is connected to the first output 11 and the output is connected to the second input of the mixer 5. The output of the bandpass filter 23 is connected to the second input of the mixer 14, the output of the controlled generator 16 is connected to the input of the electron-counting frequency meter 21. The output of the phase detector 18 is connected to the second input of the summing amplifier 12. The output frequency memory unit 9 is connected via a phase shifter 13 per l / 2 to the second input of the phase detector 19. The output of the input amplifier 29, whose input is the device input, is connected to the modulating input of the phase modulator 24 and the amplitude detector input ra 26.

The device works as follows.

Analyzed linear-frequency-modulated (chirp) signal type

U (t) Ucos t +

+ 0.5Јt2 + / AF (t) oJ

at 0 t gi /

where U, FH, ft,, TU is the amplitude, the initial frequency, the FM speed, the initial phase and the duration of the signal;

L F (t) - a function describing the intra-pulse frequency deviations from the linear law (Fig. 3a), comes after amplification in the amplifier 29, to the modulating input of the phase modulator 24, to the signal input of which a monochromatic microwave frequency signal is received from the generator 25. As a phase modulator, you can use a traveling-wave tube (LEV) of type O or solid-state linear phase modulators on varactors.

At the output of phase modulator 24 there will be a signal consisting of a continuous component of frequency f0 and partial chirp pulses with different frequency deviations and intra-pulse frequency deviations from the linear law Afci m DR + m AF (t), where DR / 9ru ( at I ± m), spaced apart by frequency on FH and having relatively mirror frequency frequency modulation laws (Fig. 2). Using the input amplifier 29, you can change the modulation index by adjusting the gain, thereby adjusting the amplitude of the partial chirp pulses at the output of the phase modulator 24. The first partial chirp pulse is output to the band-pass filter 23 under the condition FH m AF m-times the frequency deviation of the mAF and intra-impulse frequency deviations m AF (t) from the linear law (Fig. 36). The signal input of the second mixer 14 receives a signal with frequency f0 + + AF (t), and the signal input of the third mixer 5 receives a signal delayed in the delay line 20 by ge with a frequency of f0 + + ft - / T3 + AF (t - T3). The heterodyne inputs of the mixers 14 and 5 from the phase shifters 10 and 15 receive signals with the frequencies f0 - RSdv / 2 and f0 + RSdv / 2, respectively, where RSdv is the offset frequency in phase shifters 10 and 15. Using the oscillator f0 as the heterodyne signal 25 makes it possible to compensate for frequency instabilities f0. which are introduced during conversion at phase modulator 24. Then, at the output of bandpass filter 1, there will be a signal with a frequency of + / ft + Df (1) + RSdv / 2, and at the output of a bandpass filter 6 - a signal with a frequency of

 + / St -ft r3 + D F (t - ge) - Рсдв / 2.

These signals arrive at the inputs of the first mixer 2 and finally at the output

amplifier 3 intermediate frequency we have a signal with frequency

Rsdv + m ft ge + m D F (t) ge. five

The controlled oscillator 16 generates clock pulses with the following frequency fn - 0.5 RSdv p, where n is the number of stages of sawtooth phase modulation 0. Rsdv is chosen so that it is significantly greater than the estimated deviation of the instantaneous frequency of the studied chirp signals from the linear law at the output of the bandpass filter 23, and is tens of MHz; An n-bit binary clock counter, 11 clock pulses, operating with overflow reset, counts clock pulses of the controlled oscillator 16.

0 The output direct, inverse codes of the binary counter 11 are supplied as control, respectively, to the first 10 and second 15 discrete phase shifters. The high-frequency inputs of the first 10 and second 15 discrete phasers are given a signal with a frequency f0 from oscillator 25. On the discrete phase shifters 10 and 15, the signal is shifted with a frequency f0 in frequency down and up by rsdv / 2, respectively. Making the frequency shift the monochromatic frequency f0 of generator 25, rather than the chirp signal itself, reduces dynamic errors and improves measurement accuracy.

5 From the output of the intermediate frequency amplifier 3, the difference frequency component is fed through the second delay line 4 to the inputs of the first 18 and second 19 phase detectors. Reference oscillation

0 for the phase detector 18 is generated by a synchronized generator of the frequency memory unit 9, which stores the frequency and the initial phase of the signal arriving at its input from the output of amplifier 3 intermediate

5 frequencies through the strobe-cascade 8 during the enabling pulse from the driver of the 27-pulse opening the strobe-cascade 8. The duration of the enabling pulse is chosen so that during this time in the block

0 9 frequency memory set stationary mode. In order not to lose information about the measured parameters at the beginning of the pulse, the delay time of the delay line 4 is chosen equal to the total time.

5 transients in mixer 2 and frequency memory block 9. The signal from the frequency memory block 9 is fed to the first input of the first 18 phase detector. Output voltage of the first 18 phase detector

proportional to the instantaneous phase difference of oscillations of the memory frequency block 9 of the signal from the output of the first delay line 4. Due to the inertia of the phase detector 18, the pulse voltage at its output has spikes at the beginning and end of the pulse. These transients, resulting in the loss of some information, as well as the amplitude distortion of the signal at the output of the phase detector 18 are compensated at the subtractor 22. For this, parallel to the phase detector 18 a similar phase detector 19 is switched on, to which the reference signal from the frequency memory block 9 fed through a phase shifter 10 per / 2. In this case, the phase detector 19 becomes insensitive to the phase difference of the input and reference signal, and its output signal characterizes the amplitude distortion of the input signal and its own transients. This signal is subtracted on the subtractor device 22 from the output signal of the phase detector 18. The differential signal characterizing the frequency distortion of the analyzed chirp signal, through the video amplifier 28, the first integrator 31 is fed to the observation and measurement on the oscilloscope 21. Synchronization of the oscilloscope 30 and the gate-cascade 8 is effected by pulses from a generator 27 triggered by a leading edge of the envelope of the analyzed chirped radio pulse, which is extracted by an amplitude detector 26.

Changing the difference frequency and phase of the signal at the output of the mixer 2 when analyzing chirp signals with different rates of frequency change is compensated for by the inertial circuit of the frequency-phase self-tuning of the frequency of the controlled oscillator 16. formed by the frequency detector 7, the summing amplifier 12 and the second integrator 17. The frequency variation The signal at the output of the intermediate frequency amplifier 3 causes a change in the pulse frequency of the controlled oscillator 16 fn. In this case, the repetition frequency of the control code at the output of the counter 11 f fn / n will change, equal to the frequency of the signal of the frequency f0 of the generator 25 at each of the discrete phasers 10 and 15 | RSdv 1 I 1Pdv21 0.5 Psdv tc. This compensates for the change in the difference frequency Psdv at the output of mixer 2, and, consequently, the difference in the frequencies of the signals at different inputs of the first phase detector 18, which occurs when the rate of change of the frequency of the analyzed chirp signal changes. At the same time, the accuracy of compensation of the difference in the oscillation frequencies at different inputs of the phase detector 18 is increased when the summing amplifier 12 adds the signals from the frequency detector 7 and the phase detector 18, thus providing

frequency-phase self-tuning of the controlled oscillator 16. The frequency of the controlled oscillator 16 is proportional to the rate of change of the frequency of the analyzed chirp signal, taking into account the multiplication factor of the frequency deviation of the frequency hl obtained using the phase modulator 24. The rate of change of the frequency of the analyzed chirp signal can be determined by measuring frequency generator 16 electron counter frequency meter 21.

Thus, the use of phase modulator 24 makes it possible to increase the sensitivity of the 23 gp-th partial chirp pulse when a bandpass filter is selected.

Claims (1)

and measurement accuracy not less than m times. Apparatus of the Invention A device for measuring the average rate of change of frequency and linearity of the modulation characteristics of frequency-modulated oscillators, comprising a first and second phase shifters, an electron-counting frequency meter, first and second delay lines connected in series, first mixer, intermediate frequency amplifier, strobe stage, memory block frequency, the first phase detector. subtraction unit, video amplifier, first integrator and oscilloscope, as well as series-connected amplitude a detector and pulse shaper, an amplitude detector and a pulse shaper connected in series, a nil phase shifter connected in series, and a second phase detector, serially connected frequency detector, summing amplifier, second integrator, controlled oscillator and counter, the first and second outputs of which are connected to the second inputs of the first and second phase shifters, respectively, the output of the controlled generator is connected to the input of the electron-counting frequency meter, the output of the pulse shaper is connected to the synchronized inputs of the strobe stage and oscilloscope, the output of the intermediate frequency amplifier is connected to the input of the frequency detector and through the first delay line to the second inputs of the first and second phase detectors, the input of the phase shifter on nil is connected to the output of the frequency memory unit, the output of the second phase detector is connected to the second input of the subtractive unit, the first input of which is connected to the second input of the summing amplifier, which is connected in series with the purpose of increasing the sensitivity and accuracy of measurement generator, phase modulator, first band-pass filter, second mixer, second band-pass filter, as well as an input amplifier, a third mixer and a third band-pass filter, the output of which is connected in series the second input of the first mixer, the first input coupled to an output of the second bandpass filter output 0 The first bandpass filter is connected via the second delay line to the first input of the third mixer, the second inputs of the second and third mixers are connected to the outputs of the second and first phase shifters, respectively, the first inputs of which are connected to the generator output, the input of the amplifier, whose input is the device input, connected to the modulating input of the phase modulator and the input of the amplitude detector. . / o- VF " f , f04mF, to / yy L / g. five