Bill M wrote:
Rob wrote:
dspurg7310 wrote:
I am really new at electronics projects. I am trying to build a repeater
out of two mobile VHF radios and I'm not sure how to solve a problem I
am having:

My main problem is with the radio that I want to transmit. It does not
have VOX mode on it and I'm not sure how to get the first radio to
trigger the second radio to transmit. Is there a simple way to do this
or do I actually need a radio with VOX capability?

You need to build a circuit that connects the Squelch signal from your
receiving radio to the PTT input of the transmitting radio.
This could be as simple as a transistor and a resistor, it could add
some timer(s) and tone generator(s), or it could be a complicated circuit
with a microcontroller.
It all depends on how you want the repeater to behave.

Ah, brings back memories! Permit me a few words of bandwidth.

I built our club's repeater in the 70s. WR4ARO, iirc. Don't recall
much but it was a Motorola Sensicon (A?) receiver strip and an RCA
transmitter strip. It wasn't quite as simple as tagging off the squelch
to key the xmtr, although that could work functionally. I built a COR
(Carrier Operated Relay) circuit from a 73 Magazine article.

The gist of it is that you need some 'hang-time' with a repeater to deal
with mobile drop outs, and you need to be able to sub in the callsign ID
at intervals and deal with timers and such to allow the thing to shut
off transmitting in the case of noise or a deadman on the mike.

That is why I wrote about timer(s) and tone generator(s). There are many
things you can add... In the 70s/80s people built very complicated
electronic circuits, but today it is normally done with a microcontroller
and software. Of course this can mean very complicated software...