SU1734046A1 - Device for selecting and measuring accompanying frequency modulation of amplitude-modulated oscillations - Google Patents

Abstract

The invention relates to a radio metering device, in particular, to devices for measuring distortions of modulated oscillations. Purpose of the invention is to increase speed. The device contains a reference generator 1 pulses a counter 2 pulses a constant storage unit 3, a digital-to-analog converter 4 a generator 5 amplitude-modulated signals mixer 6 LO 7, receiver 8 frequency-modulated signals resistor 9 switch 10, pulse control generator 11, unit 12 controlling local oscillators two N-channel en analog multiplexer-demultiplexers 13 and 14 one-shot 15, capacitors 16i 16N 17i 17w buffer blocks 18 19 arithmetic unit 20 voltmeter 21 1 silt (l

Description

The invention relates to a radio measuring technique, to devices for measuring the distortion of modulated oscillations, and can be used to certify standard signal generators with a view to improving their quality.

The aim of the invention is to increase the measurement speed.

The drawing shows a block diagram of the device.

The device contains a reference pulse generator 1, a pulse counter 2, a permanent storage unit 3, a digital-to-analog converter 4, an amplitude-modulated (AM) signal generator 5, a mixer 6, an oscillator 7, a receiver 8 frequency-modulated signals, a resistor 9, a switch 10, control pulse generator 11, heterodyne control unit 12, first 13 and second 14 N-channel analog multiplexers-demultiplexers, one-shot 15, capacitors 16.1-16N, 17.1-17N, buffer blocks 18.19, arithmetic unit 20, voltmeter 21.

The device works as follows.

In the pulse counter 2, a linear-rising code is generated using the reference pulse generator 1. When the counter overflows, it is automatically reset, i.e. the code at the output of the pulse counter is periodic. The frequency division factor of the counter 2 pulses is chosen so that the repetition period of the linearly increasing code at its output is equal to the period of the modulating oscillation of the test signal. In the permanent storage unit 3, this ramp code is converted to a harmonic wave code. In this case, one period of the sine or cosine function is recorded in the permanent storage unit 3. A digital-to-analog converter 4 converts a harmonic waveform code into an analog harmonic signal, which is fed to the modulating input AM of generator 5, where the test signal is generated. Mixer 6 uses local oscillator 7 to transform the frequency of the AM test signal. The receiver of the frequency-modulated signals (FM receiver) 8 tunes to the difference frequency between the AM signal and the local oscillator, selects and detects the converted test waveform in frequency. Since AM generator 5, mixer 6 and FM receiver 8 have amplitude-phase conversion, the useful amplitude modulation of the test signal is converted to accompanying frequency modulation with frequencies that are multiples of the modulation frequency AM of oscillation, which is allocated at the output of the FM receiver 8. This oscillation through a resistor 9 and switch 10 is fed to the input of one of the analog multiplexer-demultiplexers, to the outputs of which are connected capacitors

16 and 17. The connection of one of the capacitors 16,17 to the input of the analog multiplexer-demultiplexer occurs on the command at its address input, which is connected to the output of the counter 2 pulses.

Since the linear-rising code at the output of the pulse counter is periodic with a period equal to the period of the modulating oscillation, the connection of the capacitors 16,17 to the analog inputs

multiplexers 13,14 occurs periodically with a period of modulating oscillation. If the charge time constant of these capacitors through a resistor 9 is chosen large enough, then on each of

capacitors during operation of the device will establish a constant voltage equal to the instantaneous value of the voltage at the output of PM receiver 8 at time tk + M

-gK tv

T --- where K is a number

   N

a capacitor; N is the number of capacitors connected to the outputs of one analog multiplexer-demultiplexer. T is the modulating oscillation period, which is equal to the output oscillation period of the FM receiver 8; M is any integer. Since the instantaneous values of the periodic oscillation voltage are repeated through a period, the voltages

installed on the capacitors, will be constant equal to the average value of the voltage during the connection of this capacitor. The one-vibration 15 turns off the multiplexers-demultiplexers 13

and 14 for transients at their inputs.

The device allows you to isolate and measure separately the accompanying frequency modulation AM oscillations that occur in

AM generator, mixer, transmission path and FM receiver. In this case, the property of a frequency converter (mixer) is used to invert the law of frequency modulation of its input oscillation at

rearrangement on the mirror channel

When measuring the associated frequency deviation in the AM generator 5 using the generator 11 of control pulses and the heterodyne control unit 12, the frequency of the local oscillator is switched to twice the frequency of the input oscillation of the FM receiver (meter of frequency deviation) 8, i.e. The mixer 8 is rearranged to a mirror channel. The same control pulses switch the inputs of analog multiplexer-demultiplexers 13.14 using switch 10. When tuning the local oscillator 6 on the forward channel, the output of the FM receiver 8 is connected via a resistor 9 to the analog multiplexer-demultiplexer 13, and tuning the local oscillator 6 to the mirror channel to the output of the FM receiver 8 through the resistor 9 connects the input of the analog multiplexer-demultiplexer 14. When the information input of the analog multiplexer-demultiplexer is disconnected from the output M of receiver 8, the voltage at the information input continues to vary exactly according to the same law as during connection of the input. This is because the polling on the address inputs of the multiplexer continues to be made, and the capacitors connected to the outputs of the analog multiplexer-demultiplexer keep the voltages set on them, since the buffer blocks 18 and 19 have a large output impedance and do not allow them disengage. Thus, the voltage at the input of the buffer unit 18 is fixed at the output of the FM receiver when the mixer is tuned to the forward channel, and the input of the buffer unit 19 is applied to the voltage established at the output of the FM receiver when the mixer is tuned to the mirror channel. The difference of these voltages, which is obtained at the output of the arithmetic unit 20 (operates in the subtraction mode), is directly proportional to the doubled value of the accompanying frequency modulation arising in the AM generator, since when the mixer 6 is tuned from the direct channel to the mirror associated frequency modulation , arising in the AM generator, is inverted, and the attendant frequency modulation, arising in the FM receiver, remains unchanged. Voltmeter 21 measures this voltage.

When measuring the associated frequency modulation occurring in the FM receiver 8, the process of isolation and measurement is similar to that discussed above, except that the measured value is extracted by adding two voltages, i.e. the arithmetic unit 20 operates in the summation mode.

When measuring the associated frequency modulation in mixer 6 or path

additionally, the mixer output applies, in addition to what has been said, inverting the law of frequency modulation using a local oscillator to measure the frequency deviation,

which must be tuned to the mirror channel at the same time as the local oscillator is rebuilt 7. In this case, the accompanying frequency modulation, which occurs in AM generator 5, inverts 0 s twice, i.e. remains unchanged, as well as the accompanying frequency modulation occurring in the frequency deviation meter 8, and the accompanying frequency modulation occurring in the mixer 6 (with the transmission path at the mixer output) is inverted in the frequency deviation meter mixer. Thus, the difference in output voltages of the frequency deviation meter is directly proportional to the associated frequency

0 modulation arising in the mixer (transmission path at its output). In this case, block 20 must be subtractive.

Claims (1)

The invention The device for the selection and measurement 5 of the associated frequency modulation of amplitude-modulated oscillations, containing serially connected reference pulse generator and pulse counter, sequentially connected 0 constant memory block, digital-to-digital converter, amplitude-modulated signal generator, mixer and receiver of frequency-modulated signals, as well as a voltmeter, one novibrator, a control pulse generator, an arithmetic unit, a local oscillator control unit and a local oscillator whose output is connected to the second input of the mixer, and the input to the first output of the control unit by the heterodyne, the second output of which is connected to the second input of the receiver of frequency-modulated signals, and the input to the first output of the generator pack Auxiliary pulses, the second output of which is connected to the input of the one-shot, the input of the permanent storage unit is connected to the output of the pulse counter, from which, in order to improve speed, two buffers are inserted into it unit, switch, resistor, two analog N-channel multiplexer-multiplexers and 2N capacitors, the first plates of which are grounded, and the second connected to the outputs of the first and second 5 analog multiplexer-demultiplexers, the address inputs of which are connected to the output of the pulse counter, the enabling inputs are connected to the output of the one-shot, and the information inputs are connected respectively to the first and second the switch outputs and the inputs of the first and second buffer blocks, the outputs of which are connected to the first and second inputs of the arithmetic unit, the output of which is connected to the input of a voltmeter, the input the switch is connected via a resistor to the output of the frequency-modulated signal receiver, and the control input is connected to the second output of the control pulse generator.