Title: Transmit-receive switching circuit with audio muting

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Abstract: A two-way AM communications apparatus is provided with common circuitry for biasing the transmitter and receiver on and off alternately while minimizing the switching noise heard in the audio. The push-to-talk button enables either the transmitter or the receiver by means of a transmitter switching network which controls a receiver switching network. When the transmitter is enabled, the audio is muted through a fast-react, slow-decay circuit, and an OR gate and the power amplifier is enabled through a slow-react, fast-decay circuit and a NOR gate. Similarly, when the receiver is enabled, the power amplifier is disabled and the audio unmuted through the same circuitry. A first OR gate is coupled to the channel select switch and noise blanker or other radio circuit to trigger a one-shot multivibrator which in turn is coupled to second inputs of the NOR gate and first OR gates to provide brief audio mute (if receiving) or brief power amplifier disable (if transmitting) during switching periods.


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