Tuesday, June 23, 2020

Experiments: FRS Radio Video Conference Gateway

In normal times, Silicon Valley Lines runs one operating session per month. In these times ... not so much. Density of people in the layout room is the main problem with social distancing. Cutting down on the number of people, wearing masks, proper hand santitation, and keeping social distance is a requirement in these times.

What would it take to have a remote dispatcher patched into the FRS radios used by the engineers in the layout room? Video Conferencing solutions like Google Meet, Zoom, Skype, and others bridge the long-distance connection easily. However, how do I connect a FRS radio to a computer?

Should be easy: Connect the headphone speaker of a radio to the microphone in on the laptop, and the line out of the laptop to the microphone of the radio. Not so fast! The voltage levels between line, speaker, and microphone vary quite a bit. It's not just about plugging stuff together with the correct wires, but rather needs some circuitry to translate the signals properly in both directions.

The next idea I had was to connect a headset to the radio, so that I have physically separated places for speaker and microphone, and tape the microphone of a computer headset to the earpiece from the radio, and the computer ear piece to the radio headset microphone. With a headset plugged in the radio automatically goes into VOX mode when turned on. When the radio "hears" something being said, it starts transmitting. There is a delay of 2-3 seconds before radio transmission starts, so people on the "computer" side need to add a couple filler words to all their transmissions. This worked, but volume level from radio back to the computer side was very low and very garbled.

Eventually I found a setup that works reasonably well. I'm using a new cheap ear piece and microphone for the radio side, and regular earbuds for the computer side. The 4-pole 3.5mm jack of the earbuds goes into a splitter cable that converts the wiring to two 3.5mm stereo plugs. The microphone is plugged into a small external denoise adapter and into the computer. I taped the ear piece of the radio side to the microphone of the computer side, and taped the microphone of the radio side to the laptop speaker. The photo above shows the early test setup using a TED talk on Youtube. The volume on the computer needs to be loud enough that the radio starts transmitting, but not so loud that it overwhelms the radio microphone, but with some experimenting the right level was found quickly. A remote dispatcher (or remote engineer) should probably have a microphone close to his month and not use the built-in microphone of their computer.

Participants on the video conference will be able to see the video feed from the layout room and hear the conversation of dispatcher and crews.

I'm still interested in the proper circuitry for connecting the radio directly to the computer, but that's for another time. In addition, at least my Motorola Talkabout radios don't work if they are plugged into a charger, which makes me really sad.

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