SU1413541A1 - Digital frequency meter - Google Patents

Abstract

The invention can be used in radar. A digital frequency meter (CIC) contains a detector 14, a tunable band-pass filter 15, a phase-correction unit (C) 16, B 17 forming reference pulses, keys 18, mixers I, generator 2, filters 3 low frequencies, samplers 4, controlled oscillator 5 sampling, analog-to-digital converters 6, B 7 calculations of discrete Fourier transform, B C with memory, quad 9, B 10 counting and finding the maximum value, memory 11, B 12 comparing estimates, interpolator 13. CI has a higher speed, 2 Il. (L so O 1h

Description

The invention relates to a measurement technique and can be used in radar.

The purpose of the invention is to increase the speed of the meter.

FIG. 1 shows a functional diagram of the proposed digital frequency meter; in fig. 2 - diagrams explaining his work.

The digital frequency meter contains mixers 1, generator 2, low-frequency filters 3 (LPF), samplers 4, controlled sampling generator 5, analog-digital pre-p drivers (ADC) 6, block 7 of the calculation of the discrete Fourier transform (DFT) , block 8 with memory, quadrtor 9, block 10 for sampling samples and finding the maximum value, memory 11, block 12 for estimating interpolator 13, detector 14, tunable band-pass filter 15, phase-correcting block 16, block 17 formating reference pulse in and electronic keys 18.

The corresponding outputs of quadrature generator 2 are connected to the second inputs of mixers 1, the outputs of the mixers of teli 1 are connected to the low-pass filter 3, the outputs of which are connected to the samplers 4, to the second inputs of which are connected to the corresponding outputs of the controlled generator 5 of sampling, the outputs of the samplers 4 are connected to the corresponding inputs of the ADC 6, the outputs of which are connected to the DFT block 7, the output of which is connected to the block B with memory, the output of which is connected to the input of the quadrant 9, the first output of which through Connected block 10 for sampling and finding the maximum value, memory 11 and evaluation block 12 are connected to the second input of the interpolator 13, the first input of which is connected to the second output of the quadrant 9, to the output of the detector 14 a tunable band-pass filter 15 is connected, the output which is connected to the phase-correcting block 16, the output of which is connected to the block 17 of the formation of reference pulses, to the outputs of which are connected controlled frequencies of electronic keys 18 and controlled generator of sampling 5, ignalyshyu input detector 14, and the electronic key 18

combined, and the outputs of the electronic keys 18 are connected to the corresponding inputs of the mixer 1.

The meter works as follows.

A regular sequence of radio pulses arrives at the input of the detector 14 (Fig. 2a). After the detector 14, the signal in the form of a pulse sequence is fed to the input of a tunable bandpass filter (Fig. 2b). The proposed meter is designed to work on an object about which there is a priori data on the structure of the radiated sequence of radio pulses. Due to the Doppler effect, the a priori known structure of the received signal is disturbed, the carrier frequency of the radio pulses changes, as well as the period of the radio pulses. Moreover, the frequency of the change varies slightly:

F yl

tp

(one)

about c q j

0

five

where YU is the radial velocity of the object; c is the speed of light; F is the frequency of the radio pulse of the emitted sequence.

Before starting the measurement, the bandpass filter 15 is tuned to the frequency F, and the filter passband 4f (p is larger than the possible range of frequency variation ± F.

During the measurement, the output of the frequency bandpass filter 15 generates a signal (FIG. 2c) 5 arriving at the phase correction unit 16, which eliminates the signal phase shifts, after which the signal passes to the reference pulse formation unit 17, in which the signal transitions from a negative value a positive pulse is formed, the duration of which is equal to the duration of the received radio pulses. As a result, at the output of the reference pulse generation unit 17, a periodic pulse sequence is formed (Fig. 2d), which is fed to the controlled input of the electronic key 18 and to the controlled sampling generator 5. At the moment of arrival of an electronic pulse, the key opens and passes a corresponding radio pulse to the mixer 1. (Fig. 2e). After mixer 1 and low pass filter 3

the signal is reduced in frequency to the sampler 4. The controlled sampling generator 5 is turned on at the moments of arrival of pulses (Fig. 2d) The sampling frequency is selected according to the Kotelnikov theorem and in this case the maximum frequency of the passband LPF 3 is determined,

The second part of the scheme works similarly, symmetric to the described one. After the DFT calculation unit 7, the components of the complex spectrum arrive at the memory summation unit 8, where the wordwise addition of the DFT coefficients is performed, which is formed from the radio pulse to the radio pulse ..

In the coherence section of the input signal, the addition of discrete samples of the complex spectrum of the useful signal occurs in phase, and the noise components are random and, as a result, compensate each other.

The generated total spectrum is fed to quadrant 9, where the square of the discrete complex spectrum components is calculated and the energy spectrum counts are formed. In block 10, the search of the samples and the finding of the maximum value determines the rough estimate of the frequency F p, which is stored in the storage device 11. After receiving several rough estimates of the frequency in block 12 of the comparison of the estimates, the comparison of the estimates

LRN.L.,

(2)

t. where, is a rough estimate of the frequency obtained by finding the maximum component of the power spectrum. If condition (2) is fulfilled several times, this is determined by

given by the reliability of the frequency estimate, the last estimate is considered true and its value is in

terpolor 13, the second input of which receives counts of the total energy spectrum. Interpolator 13 forms an accurate estimate, since when sampling LG it is possible to accurately reconstruct the spectrum in the interval between spectral readings using the Kotelnikov series. This allows you to determine the exact value of the coordinate of the maximum energy

spectrum, i.e. obtain a frequency estimate that is consistent with the maximum likelihood estimate in this case.

   .I

Since the proposed device

If the signal is not analyzed for the entire period of the radio pulse repetition, but for the effective duration of the radio pulses, then its speed will be significantly higher.

Claims (1)

Invention Formula Digital frequency meter auth. St. No. 1091086, which is also distinguished by the fact that, in order to improve speed, a detector connected in series, a tunable band-pass filter, a phase-correcting unit and a reference pulse shaping unit have been introduced into it; as well as the first and second keys, with the detector input connected to the first inputs of the first and second keys and to the input of the device, the first and second outputs the reference pulse shaping unit are connected respectively to the second inputs of the keys, and the third output to the auxiliary input of the controlled sampling generator, the outputs of the first and the second keys are connected respectively to the first inputs of the first and second mixers. FIG. 2