Portable Repeater Project - Receiver & Transmitter

A lot of hams have picked Motorola Maxtrac radios for VHF or UHF repeater projects. But programming the radios is a pain, because Motorola are rigid about allowing amateur use of the (outdated) programming software, an attitude which sort of ticks me off. I spent some time looking around for naked UHF radio modules like the ones Bridgecom use in their repeaters, but found nothing that looked promising. I concluded that I was going to have to use mobile radios.

Every major manufacturer of mobile radios has some model which would do well for this purpose, but I was looking for a radio with a rear connector for transmit and receive audio, COS (Carrier Operated Squelch), and PTT (Push To Talk) signaling. This turns out to be the signals on the common six pin mini-DIN connector that you see for TNC connections on mobile radios. A big advantage of using this TNC connector is that it gives you access to the audio chain with the pre-emphasis/de-emphasis stuff excluded, and the only thing running the audio through de-emphasis at the receiver and back through pre-emphasis at the transmitter accomplishes is degrading the audio quality.

I like Kenwood VHF/UHF radios, and I pondered using Kenwood TM-V71A radios, but they’re dual band and that’s surplus to the requirements, and they’re relatively pricey. Another candidate was the Alinco DR-435T. I’ve used the 2m brother to this radio for packet and VARA FM with great success, so I was positively inclined until I read a review that said the CTCSS decode stuff in the Alinco radios is awful and won’t work for repeaters. But then I also found some reviews that indicated that this problem didn’t occur with the Mk III version of the radios.

So I ended up buying 2 Alinco DR-435T mk III radios , just a moment before the worldwide supply chain went kerflooey/kaboom and every model of Alinco mobile radio became unobtainable.

Conveniently the TNC connector on the back of these radios is a dsub-9 connector, which is a little easier for me to deal with than the 6 pin mini-DIN I was expecting to have to deal with.

The pinout for the TNC connector is specified as:

I’ll need to build a cable harness to go from the controller to both the transmit radio and the receive radio but the good news is that it will be dsub-9 connectors at the repeater controller and the radios, and that will be a straightforward job if I can just remember how to keep the pin numbering correct.