SU63877A1 - Method of measuring modulation depth - Google Patents

Description

The proposed method for measuring the modulation depth of the frequency-modulated oscillations differs from the existing ones in that, in order to establish the measurement scale, the values of the variable and the constant current (or voltage) components at the output of the detector, whose input signal is applied, are measured separately. subjected to electrical differential cyroen.

Let there be a frequency-modulated oscillation, the frequency of which varies according to the law

with Shd - {- Dsh COs2t a) a (l - {- incOS 9t),

(where W (, is the carrier frequency, 2 is the frequency of the primary signal), and the voltage and current have a VIEW:

/ W

E: Eacosfu) ot-b -sinQt

I Jfl cos (ufl t + - Sin 9. t

To measure the depth of the module 4sh

m - i need to proCeOJQ

The following operations:

a) Differentiate current or voltage over time, while

the frequency w will be out of the cosine (or sine) argument

Dm

dl d

oot + 7gs, ° di

ysinQtj,

 9 (0 + ° S - t) Sin ot +

b) Detect the voltage received in this way; at the same time, the constant is constant, proportional to the current Od 1, and the component is variable, proportional to rtio cos 2t.

c) Measure the voltage (or current) of the variable component aTd Dsh cos 2. The amplitude value of this voltage (current) will correspond to Dsh. The scale is measured and can be set according to the magnitude of the non-constant component voltage (current). In this case, the scale can be directly obtained

Dsh

modulation depth value

0

FIG. Figures 1-2 of the drawing show electrical circuits of devices for measuring the depth of modulation according to the proposed method.

In the diagram of FIG. Figure 1 shows a self-induction coil L, through which the frequency-modulated current flows 1. The coil is connected to the grids of the mixing lamp L, the output of which includes a high-frequency shunt Co, a device G for measuring DC current and a cathode peak voltmeter KV. For electrical signal differentiation, as can be seen from the diagram, the inclusion of a self-induction coil I current L in the circuit is used, since the voltage drop across the coil is paBHd of the first derivative of the current. It is assumed that the current in the coil L is limited by the source impedance so that the voltage drop across the coil L changes with frequency. With the flow of the frequency-modulated current / L (in of ;; I IOCOS through the coil L on the grids g and g. In terms of voltage and „“. Li "oh- - Coset Xocosi cofl t + -sinQt / iio), and n LI "0 U + COS" t nLX "0 / l" Xlocos coot-f, -sin n is the transformation coefficient. In this case, the anode current of the lamp L will be I S (l + aU ,, 2) U, i, where S is the steepness of the lamp. Substituting the values of Ugi and U we obtain: / To) o L In cos I o o t -f 7G The high-frequency component of the anode current is filtered to the capacitors Co. The low frequency will be equal to I a Sn L2 Jo -.and 1-1-2 costHMO cos2 Q t Dividing b into a constant ILV, variable components of a ray (converting cosbit to D a.S-n-L-lo); AcoVl 1 TJYj 1ce D s ,. : П О2Г2 со801 Ч-Г-Vcos2t 1 L -. «ОУ Г Since the ratio is usually less than one and in all participants is less than 5.10, then the members ,. obsessed with them. as a multiply. It is possible to neglect the values of the tube without the earbar for accuracy. Therefore, the derived outputs can be rewritten in the form: Qv D 0/2 COS t. By comparing these last expressions and knowing the constant ... that was Lc, you can set the mastab of the variable component. In turn, measurement of a variable component, for example, a peak cathode voltmeter, gives the ratio - -, t, that is, the magnitude of the gluoin modulation. In the measurement of direct current, the instrument G turns on and the capacitor C has a shunt sound frequency. When measuring AC, the resistance R ,, is equal to the internal resistance of the instrument G, and the device KV is connected in place C. FIG. 2 shows a circuit with diode detection. In this case, the expressions derived above for the constant and variable components of the detected current will have the following form: 1 ° (. AOJ 1d "A s cos q t.

Thus, the measurement of these currents is determined to establish the scale of measurement and to determine the magnitude of the modulation depth.

subject matter

The method of measuring the depth of duplication, characterized in that, in order to establish the scale of the measurement,

the magnitude of the constant and variable components of the current (or voltage) at the detector output, to the input of which the voltage of the signal is subjected to preliminary electrical differentiation, and the magnitude of the constant component is judged by the scale determined by the variable component of the depth of

u

7

FIG. 2