Here is my first attempt to construct a voice activated repeater controller using a VU driver IC LB1403N. Instead of driving a group of LEDs, the first pin is used to pull down the PTT (push to talk) of the transmitter. A small portion of the received audio is routed to the transmitter via the 100K, 0.1uF and 10K potentiometer.
The entire circuit is relatively simple and the only drawback is that it needs a high level of audio input coming from the receiver to keep the PTT close all the time during transmission. The protoype board is connected to my Icom IC-2200H as the transmitter and Icom IC-V80 as the receiver. ---73 de du1vss
