SU70171A1 - Device for phase modulation - Google Patents

Description

The disadvantage of the existing phase-modulation circuits (especially when used in frequency modulation) is the use of the anode circuit of the lamp for phase modulation, which makes it difficult to maintain an overvoltage mode (limiting mode) and distortion compensation. As a result, most schemes allow only a small phase deviation.

The device proposed in accordance with the present invention is free from this drawback. It is made according to the well-known lamp amplifier circuit with a deep negative feedback and is characterized in that a quadrupole, which modulates the phase of the feedback voltage under the influence of a modulating voltage, is included in the feedback circuit.

In the proposed device

(Fig. 1) as a phase modulator, a high-frequency amplification cascade is used, covered by a deep counter-coupling and containing a quadrupole in the feedback path, the output voltage of which varies with respect to

to the input phase with the modulation frequency.

Suppose that the amplification factor of the indicated cascade is equal to KI, the feedback coefficient is equal to | c and the message that / 3 is phase-modified by the law

--J sin and

/ 3 s

where is the modulating frequency.

Then the gain of the cascade will be equal to:

Ki

1 -if sin at

/

l + Ki) I / S |

Since the IjSJ module is usually modified, it is desirable that the cascade operate in an overvoltage mode, which will ensure that its output voltage amplitude is independent of the modulation depth.

In practice, a quadrupole in a grid circuit can be made in various ways, for example, a combination of a large active resistance R and a resonant circuit, tuned to the amplification frequency (Fig. 2). Here, the phase of the output voltage is changed by changing the parameters specified153

a sound circuit with a frequency that can be, as usual, made with reactive lamps, or using an inductor loop with an iron core, whose permeability changes with modulation. If necessary, can be applied, for example, two such links, connected in series.

A modification of this scheme is shown in FIG. 3. Here, as a modulated element, the resistance Z is used, which is included in the cathode circuit and provides deep opposition. In the simplest case, an oscillatory circuit tuned to the amplified frequency and changing parameters with an audible frequency can be used as resistance 2. The gain factor of such a scheme is:

Kg

/

Kg

 sin at

And it is practically determined by the phase angle of the impedance 2.

When using jet lamps as modulators, the simplified scheme takes the form shown in FIG. 4. This circuit resembles a serial modulation scheme of an NC anode. Here L is the high-frequency amplifier, La is the jet lamp.

In order to increase the length of the linear portion of the phase modulation characteristic while maintaining the constant of the modulus of the feedback coefficient, it is often advisable, along with the reactance of the modulus of the modulated element, to change its resistance. Indeed, since the impedance Z of the resonant circuit is equal to:

T + jx

and phase angle

(p - arctg

(where X is the introduced reactance changed by the modulator lamps and r is the introduced resistance), by increasing with a corresponding decrease in r, it is possible to both linearize the modulation characteristic with deep modulation and to maintain the modulus constant ( Z).

For this purpose, an additional controllable lamp operating in the mode of a sharp-pointed current pulse (i.e., with a cut-off angle) and introducing resistance into the circuit can be connected parallel to the contour. During modulation, the offset of this lamp should be increased (in both half-periods) and, thus, the resistance introduced into the circuit should be reduced.

FIG. 5 shows a simplified diagram of such a device. Here L is the high frequency amplifier. The reactance of the feedback loop is changed with the sound frequency by acting on the iron core of the loop inductance L. The same effect can be caused by the jet lamp L2, affecting the input resistance of the loop. With a full-wave rectifier with an L3 lamp, the displacement of the lamp L-i increases during both half cycles in order to reduce its active conductivity.

FIG. 6 shows a circuit with two stages having a common cathode resistance. This circuit doubles the phase modulation depth.

Subject invention

Claims (3)

1. A device for performing phase modulation, made in the form of a lamp amplifier circuit with deep counter-coupling, characterized in that a quadrupole is connected to the feedback circuit, changing the phase of the feedback voltage under the influence of a modulating voltage. 2. The device according to claim 1, characterized in that in order to compensate for non-linear distortions during modulation, the modeling voltage acts simultaneously on the reactive and active resistance of the modulated element of the quadrupole. 3. A device according to claim 1, wherein, in order to deepen the modulation, said quadrupole is used as a counter-resistance, common to several amplification stages. L | eight w , g jyslaKt FIG. four FIG. 3 latudf Ratt :) rf // T / FIG. five B) J FIG. b  O / rio /