SU847230A1 - Method of measuring coefficients of "up" and "down" modulation depth of amplitude-modulated oscillations - Google Patents

Description

The invention relates to techniques for measuring parameters of amplitude-modulated oscillations (AM), in particular to methods for measuring modulation depth coefficients.

A known method of measuring the modulation depth coefficients up and down ”, in which measure the average value of the amplitude of the carrier AM oscillations, the maximum and minimum deviations of the amplitude AM oscillations from this average value and determine the modulation coefficients through the ratio of the deviations of the maximum and minimum values from the average value of the amplitude of the carrier AM fluctuations to this average value [1].

However, this method is characterized by insufficiently high accuracy of measuring the modulation depth coefficients up and down.

The purpose of the invention is improving the accuracy of measurements.

This goal is achieved by the fact that the studied amplitude-modulated oscillation is converted into amplitude-modulated oscillations with 100% modulation depth according to the maximum and minimum values of the studied oscillation and the modulation coefficients are judged by the ratio of the average values of the amplitudes of the carrier e oscillations of the converted and studied amplitude-modulated fluctuations.

The drawing shows a block diagram of a device that implements the method.

. _ The device contains a switch ^υ 1, a carrier filter 2, an attenuator 3, a phase shifter 4, an adder 5, an oscillographic indicator 6, a spectral receiver 7, a frequency converter 8, a local oscillator 9, a filter 10, a readout attenuator 11 ,. indicator and input 13 of the device.

The device operates as follows.

The studied AM signal is fed to the input 13 of the device and to one of the inputs of the adder 5 and through switch 1 to the input of the filter 2 of the carrier. . In the carrier filter 2, the carrier signal is filtered out from the side spectral components. Next, the signal of the sinusoidal carrier is fed through the attenuator 3 and the phase shifter 4 to the second input of the adder 5, where the studied AM signal and the selected signal 847230 la carrier are summed. The total signal is fed to the oscilloscope indicator 6 and the input of the spectral receiver 7. By adjusting the amplitude allocated by the carrier, attenuator 3 and adjusting its phase by the phase shifter 4, the measured value of the modulation depth is deepened to 100%, due to the compensation of the carrier AM signal by the selected carrier signal, summarized in antiphase. The measured value of the modulation depth is deepened and set at 100% according to the oscilloscope indicator 6, when the maximum and minimum values of the lower and upper half-waves (respectively) of the envelope of the AM signal coincide. With local oscillator 9, the spectral receiver 7 is tuned to the carrier frequency of the recess up to 100% modulation of the AM signal, and when the value of the reference attenuator 11 is highlighted, the carrier value is fixed by indicator 12. Then, with switch 1, the signal of the compensating carrier is not fed to the input of adder 5, but to the spectral receiver 7 investigated AM signal. In this case, the receiver setting Ί does not change, and the signal of the displayed carrier on the indicator 12 increases. Next, the readout attenuator 11 readings of the indicator 12 are set equal to the first value, and when measuring by divisions on the readout attenuator 11, the peak value of the modulation depth M _ext .

The peak modulation value M _WB is measured similarly, only with an additional modulation depth of up to 100% after the first deepening of the studied AM signal. To do this, on the adder 5 increase the level of the carrier and produce a further deepening of the modulation to 100% between the maximum and minimum values of the upper and lower half-waves (respectively), envelope AM oscillations. The compensation signal of the carrier is switched off and after installation of the first indication on the readout attenuator 11 on the indicator 12, the value of M _{cv is divided} by the division on the attenuator 11.

The method and device for FORIZATION is explained using mathematical calculations.

"Suppose that the device enters the monitoring input AM signal form) / ι) where peak values take the form of amplitude modulation * READOUT its realisleduyuschih en ^ bs ~ ¹⁴ 1 ~ 4 _{^{M K sin (, kft'b n,}} ax + 'f K), (3) where t _w ' _n H t „, _aA are the values of the current time at which (2) and (3) have the minimum and maximum values; η is the harmonic number.

The studied AM signal (1) after passing the adder 5, where it is compensated by a carrier of the form (4.) where = vol. + τν is set by phase shifter 4, takes the form ₍₅₎

From (5) it is seen that with increasing U _{z of the} carrier from the output of the adder 5, equal to the amplitude (u ^ ₂ ), decreases, and the modulation depth increases. In this case, the new peak modulation values take the form:

kompensiruyunesuschey levels required for uglubVn cc ^and wherein ^m and _2c audio U _ZBB boiling Lenia 'initial values, respectively, M up to 100%.

_By adjusting U _ZBH and Uas _B, expressions (6) M * _n and Μθ ₀ are set equal to unity. Where do the measured modulation peak values ^M int ~ t ^ BB come from?

In expressions (7), the difference between the carriers of the studied and compensating oscillations (1C-Ug ^) and (U _ZBB -U. |) Is measured by the spectral receiver 7 after the modulation is set to 100%, and the carrier value of the studied AM signal is measured by the spectral receiver 7 after the signal when the AM indicator 12 under study is equalized by introducing a reference attenuator 11 with the indication that was when measuring the difference of the carriers, i.e. (U ^ -Ur,) = ktl ^ ,. In this case, the measured peak modulation values are expressed in terms of the division coefficient of the reference attenuator and can be expressed as:

^{MBH =} · ^ ^'(8'

The total error for 'measurement apparatus M and M _{corolla cc} is not more than 0.35%.

Claims (1)

1. Remez G.A. The course of the main radiological measurements. 1956, p. 281, U (prototype).