When playing around with wireless mobile traffic lights, I also thought about options to transmit on the VHF and UHF bands. I remembered that I bought a Baofeng that I never actually used. Turns out, this radio is exactly what I was looking for, as it
- supports RX/TX on 136-174MHz and 400-520MHz
- is cheap (25 EUR)
- is portable
Furthermore, it has a line-in for an external microphone, which allows connecting the radio to the PC. There is quite some information available on how to do that properly. (I plugged it directly into the PC and it worked, but maybe it was plain luck that I didn’t fry my sound card. Most people recommend decoupling the circuits.)
To disable push-to-talk and automatically transmit when a signal is sent from the PC, you have to enable the VOX option.
As a proof-of-concept, I created a web GUI that allowed me to toggle the traffic lights in the browser. In response, the web server sent UDP frames to a GNU Radio flow graph, which created an audio signal.
Overall, the process looked as follows:
Browser → Web Server → UDP → GNU Radio → Audio Sink → Line-out → Baofeng