SU1145303A1 - Device for measuring amplitude frequency characteristic non-uniformity - Google Patents

Abstract

A device for measuring the non-uniformity of the amplitude-frequency characteristic, containing two generators of frequency-modulated oscillations, the control input of each of which is connected to the output, the corresponding generator of the modulating voltage, the other output of the first generator of the modulating voltage is connected to the control input of the indicator, the input through a serially connected meter of the amplitude modulation coefficient, the first band-pass filter and the detector is connected to the input terminal of the device features that, in order to improve the measurement resolution, two mixers, a generator, a high-frequency oscillation generator and a second band-pass filter, are introduced into it, while the outputs of the generators of frequency-modulated oscillations are connected to the corresponding inputs of the first mixer, the output of which is connected to the output terminal of the device, another output of the first frequency generator (L modulated oscillations is connected to one of the inputs of the second mixer, the other input of which is connected, to the output of the high-frequency generator oscillations, and the output through the second axial filter is connected to the reference input of an amplitude modulation coefficient meter.

Description

I The invention relates to a measurement technique and can be used to measure small values of the non-uniformity of the amplitude-frequency characteristic (AFC) of high-quality radio measuring equipment paths. A device for measuring the non-uniformity of the frequency response is known, which contains a generator of the oscillating frequency and a series-connected linear detector and an indicator of the CON output of this device. The measurement accuracy is low due to the parasitic amplitude modulus of the signal at the output of the frequency generator. The closest in technical essence to the present invention is a device for measuring AChZ tunable generators, which contains serially connected meter of amplitude modulation, band-pass filter, detector and indicator, the control input of which is connected to the output of the first modulating voltage generator with the first input of the adder and with the input of the phase shifter, the output of which is connected via a sequentially connected attenuator and generator of frequency modulated oscillations connected to the reference input The amplitude modulation coefficient meter, the second input is connected to the output of the second modulator voltage generator, the output of the adder through the frequency-modulated oscillation generator under study is connected to the input of the amplitude modulation factor meter (2 3. The disadvantage of this device is the impossibility of obtaining high resolution measurements of a four-pole four-speaker system due to limitations in setting test frequencies. The aim of the invention is to improve the resolution of the uniformity of the quadrupole frequency response by reducing the influence of the parasitic amplitude modulation of the generator. The goal is achieved in that the device for measuring the non-uniformity of the frequency response, containing two generators of frequency-modulated oscillations, the control input of each of which 03I is connected to the output of the corresponding generator of modulating voltage, another output of the first generator of modulating voltage the signal input of which is connected through a series-connected meter of amplitude modulation coefficient, the first band-pass filter and detector is connected to the input terminal of the device, Two mixers, a high-frequency oscillation generator and a second band-pass filter are included, while the outputs of the frequency modulated oscillator generators are connected to the corresponding inputs of the first mixer, the output of which is connected to the output terminal of the device, the other output of the first frequency modulated oscillation generator is connected to one of the inputs of the second mixer whose other input is connected to the output of the high-frequency oscillator, and the output through the second band-pass filter is connected to the reference input of the meter and amplitude modulation. FIG. 1 shows a block diagram of the device; FIG. 2 - an approximate view of the expected frequency response of the investigated quadrupole. The device contains generators 1 and 2 of modulating voltage, generator 3 and 4 of frequency-modulated oscillations, mixers 5 and 6, generator 7 of high-frequency oscillations, second band-pass filter 8, output connected to the input of meter 9 of amplitude modulation coefficient, first bandwidth 10 The output is connected through the detector 11 with the input of the indicator 12, the output 13 and the input 14 terminals. The device works as follows. The voltage from the output of the first generator 3 of the frequency-modulated oscillations modulated by the signal of the generator 1 of the modulating voltage of the form ... U, (t) A, (w, sin (u, .u) (i) i) goes to one of the inputs mixer 5. The second input of the mixer 5 receives the voltage from the generator 4 of the frequency-modulated oscillations modulated by the signal of the generator 2, of the form (2 ()),

3

where m is the frequency modulation index,

A (ui) and Aj (u) j) are frequency-dependent amplitudes of oscillations of the signals of the regenerators 3 and 4, respectively;

I - the frequency of modulation, c) and 2 carrier frequencies of the gene -. Cages 3 and A COOT-.

veterans

u (t is the prescribed law for changing the frequency of the generator 3.

In the mixer 5, the oscillations OD) multiply and which can be represented by mathematical expression of the form: Uj (t) / (u) (u) 2) cos (u) -u) j) i + u), (t i-msinflij.

Taking into account that the amplitudes of oscillations, depending on the frequency, vary within small limits, they can be represented as follows:

L., (U,) -,

2 () -.

A, (u) .A (ur) 4M, (u) 2.),

where AA () and I {w1-) "are the slowly varying frequency components of the amplitudes A and A2 of the oscillator signals 3 and 4. From the output of the mixer 5, the oscillation goes to the input of the checked quadrupole, which connects between the output 13 and INPUT 14 terminals of the device . With an ideal amplitude-frequency characteristic of a quadrupole, the amplitude of its output voltage of the difference frequency can be represented by the following mathematical expression

МКА / Д1 + М (и, М2 (и, Ц.

In meter 9, the amplitude modulation factor using a heterodyne oscillation of the form:

w. i)), (urJ,

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the frequency modulated oscillator by oscillating the oscillator 3 of the frequency-modulated oscillation and the oscillator 7 on the mixer 6 and filtering the J band filter 8 compensates for the slow change in frequency. In this case, the oscillation of the form is formed

Uj (t) (u)) y (u)) 5tnRu -W2U) j) t-msinnt.

The envelope of this oscillation, highlighted by the modulation coefficient meter, has the form:

A (uil K A / A, and, J.M, Kh ", KJ

The oscillation at the output of the meter 9 in the bandpass filter 10 is subjected to

filtering, while isolating oscillations with a frequency of I. Since only component is changing with frequency C1, the amplitude of which does not change with an ideal amplitude-frequency characteristic, the voltage transmitted by amplitude detector 11 is constant.

If the frequency response of the studied quadrupole is not perfect and has the form shown in FIG. 2, then the amplitude of the component with frequency S1 in the oscillation envelope at the output of meter 9 varies in direct proportion to the change in the steepness of the quadrupole amplitude-frequency characteristic with a slow sweep of the operating point by the characteristic oscillation u1 (1. At that, the voltage released by the detector 11, also changing

directly proportional to the change in the steepness of the amplitude-frequency characteristic of the studied quadrupole. In indicator 12, the change in slope is converted

into non-uniformity by integration.

The non-uniformity of the amplitude-frequency characteristics of the blocks used in the device is not included in the measured value, which ensures

obtaining high resolution measurements.

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Claims (1)

A DEVICE FOR MEASURING AN UNIFORMITY OF THE AMPLITUDE-FREQUENCY CHARACTERISTIC, comprising two frequency-modulated oscillators, the control input of each of which is connected to the output of the corresponding modulating voltage generator, the other output of the first iodulating voltage generator is connected to the control input of the indicator, the signal input of which is connected through series-connected amplitude modulation coefficient meter, first bandpass filter and detector connected to the input terminal of the device, from The fact is that in order to increase the resolving power of measurements, two mixers, a high-frequency oscillation generator and a second band-pass filter are introduced into it, while the outputs of the frequency-modulated oscillators are connected to the corresponding inputs of the first mixer, the output of which is connected to the output the terminal of the device, the other output of the first generator of frequency-modulated oscillations is connected to one of the inputs of the second mixer, the other input of which is connected to the output of the generator of high-frequency oscillations, and the output d through the second bandpass filter connected to the reference meter amplitude modulation coefficient. ) FIG. 1 is the AChP which is coupled by an amplitude child