Encyclopedia of radio electronics and electrical engineering / Civil radio communications

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The transceiver's voice control system (VOX) is used to transfer it from receive mode to transmit mode using voice. Its schematic diagram is shown in the figure. It consists of a VOX amplifier on a VT1 transistor, an "anti-VOX" amplifier on a VT3 transistor, a DA1 comparator and an electronic switch made on a VT2 transistor and a K1 relay.

The audio frequency signal from the output of the microphone amplifier (MU) is fed to the resistor R1, which controls the sensitivity of the VOX system. Then the signal is amplified by the cascade on the transistor VT1 and fed to the rectifier VD1VD2, made according to the voltage doubling circuit. The values ​​of the capacitance of the capacitor C7 and the resistance of the resistor R6 determine the release time of the VOX system. Next, the signal is fed to pin 2 (comparison) of the comparator DA1.

From the output of the low-frequency amplifier (ULF) of the transceiver, an audio frequency signal through the resistor R12, which controls the sensitivity of the anti-VOX system, is fed to the "anti-VOX" amplifier VT3. Then it goes to the VD6VD7 rectifier, similar to the VD1VD2 rectifier. The circuit constant R18C14 determines the response time of this system. The rectified signal is fed to pin 3 (reference) of comparator DA1. A positive voltage from the R3R20 divider is also supplied to the same input through the VD21 diode, which serves to set the noise threshold of the VOX system.

To pin 7 (output) of the comparator DA1, an electronic key is connected, made on the transistor VT2, in the collector circuit of which the command relay of the K1 transceiver is included. The transfer of the transceiver to the transmission mode is carried out by closing the contact groups of the relay (not shown in the figure). The contact group K1.1, when the VOX system is triggered, shunts the R18C14 circuit to the case, while turning off the anti-VOX system, which drastically reduces the chatter of the K1 relay contacts. By closing the resistor R18 to the case, the noise threshold level of the system is lowered, which contributes to a better retention of the transceiver in transmission mode, even when the voice volume is lowered. When contacts K1.1 are released, the operation of the anti-VOX system, as well as the level of the noise threshold, are fully restored.

Switch SA1 is used to turn off the VOX system, and SA2 is a PTT switch (pedal) to put the transceiver into manual transmission mode.

As K1, the relay RZS22 passport RF4.500.131 with a nominal winding voltage of 24 V is used.

System setup is as follows. By selecting the value of the resistor R19, the current of the zener diode VD4 is set to 10 mA. The microphone is installed about half a meter from the transceiver with the rear facing the speaker. Turn the transceiver's volume knob to minimum. By adjusting the R20 resistor, the VOX system is not triggered by extraneous noise ("home" QRM), while the R1 resistor slider must be set to the upper (according to the diagram) position. Further, pronouncing a sound in front of the microphone (long "A"), adjusting R1 achieves a stable transition of the transceiver to the transmission mode - set the sensitivity of the VOX system.

After that, set the volume knob to the position in which the transceiver is usually operated in receive mode (speaker on). By rotating the tuning resistor R12, the VOX system is not triggered in the presence of a loud signal in the speaker. In this case, the transceiver must steadily switch to transmission when pronouncing phrases directly in front of the microphone. By selecting R6 and C7, an acceptable release time of the VOX system is set, and R18, C14 - the anti-VOX retention time.

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