A simple speech signal limiter. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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A simple speech signal limiter. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Knots of amateur radio equipment. Signal limiters, compressors

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To increase the efficiency and range of SSB communications, the signal is limited to high (HF) or low (LF) frequency. RF limiters have the best parameters, in which signal processing occurs at an intermediate frequency. They allow you to increase the average power of the transmitter signal by 6...9 dB.

Slightly, by 1 ... 2 dB, they are inferior to low-frequency limiters (the signal is processed in a microphone amplifier). But at the same time, it is much easier to make and set up a low-frequency limiter.

On fig. Figures 1 and 2 offer low-frequency limiter circuits, the effectiveness of which significantly exceeds the previously published developments of the author [1,2].

The scheme in fig. 1 contains only two stages, the first of which on the transistor VT1 is a logarithmic amplifier. As logarithmic elements, diodes VD1 and VD2 are used, connected in anti-parallel to the negative feedback circuit. The use of germanium diodes makes it possible to obtain an output voltage of the amplifier up to 200 mV eff., and the use of silicon diodes - up to 600 mV eff.

Simple speech limiter
Ris.1

An emitter follower is assembled on the VT2 transistor, which allows you to connect an amplifier to almost any mixer. Resistor R4 is used to adjust the level of the output limited signal. The use of this resistor at the output of the limiter allows you to use it, as it were, as an IF gain regulator in transmit mode. Resistors R1 and R5 prevent self-excitation of the DC stage. To do this, in the circuit (Fig. 1), by selecting the resistor R2 *, the voltage on the VT1 collector is set to +6 V. In the circuit according to fig. 2, the same voltage on the collectors VT1 and VT2 is set by selecting resistors R2 * and R5 *, respectively. The circuits given in the article were implemented by the author in the designs of SSB transceivers: direct conversion, with EMF, with a quartz filter.

Simple speech limiter
Ris.2

Using almost any type of dynamic microphone, the limiters have shown good received SSB signal quality and no overmodulation with significant changes in signal levels from the microphone.

Literature

1. Artemenko V. A. Microphone-telephone amplifier. - "KV-journal", - 1996, No. 3, p. eighteen.
2. Artemenko V. A. A simple microphone transceiver amplifier. - "Radioamator". - 1996. No. 12.p. 19.

Author: V. Artemenko (UT5VDJ), Kyiv; Publication: N. Bolshakov, rf.atnn.ru

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Comments on the article:

a guest
Everything is class!

Serge
Everything is clear. [up]

Eugene
But what about the phase limiters of speech signals, described by V.T. Polyakov in various literature? They are much more efficient.

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