I've put together a repeater with a couple of spare mobile rigs, taking a signal from the LED that lights when the radio receives a signal, and with a buffer transistor (NPN in open collector, grounded emitter configuration, 4.7K resistor on the base) to toggle the second radio into transmit. Since a lot of radios have a short burst of noise when the transceiver toggles from transmit back to receive, I've added a key-up delay. I also added a "hang" timer so the transmitter stays in transmit for about 1 second so it doesn't "chatter" when a weak receive signals drops in and out of the receiver, like this:I am more than interested in hearing you out on building my own repeater with your ideas! I am here for knowledge!
and ground unused inputs of gates, like this:
If you use two transceivers in the same band, you'll need duplexers; in my case (in the ham bands) I used a good frequency separation (like 144MH & 220 MHz).
If the repeater's located where you can supervise it, that should be enough. If it's remote, though, I wired up a 3-minute time-out timer on eavh PTT line, like this:
(again grounding inputs of unused gates).
Please let me know if you have any questions.