The VK7NTX link gives a nice description of how to do PTT with a Baofeng radio. The best of these were from VK7NTX and ZS2EZ. Looking around, I found several possible solutions, but none was a complete soundcard interface for the Baofeng UV5R. This is far too long for ARDOP exchanges, and so I needed a reliable way to switch the radio's PTT circuit. The Baofeng's VOX mode is notoriously slow to drop out, hanging on for a few seconds in most cases. The ARDOP protocol requires the radio to switch between transmit and receive with latencies of the order of 100 mS. My second problem was how to reliably do transmit/receive switching. I needed to be able to adjust the audio output of the radio with a reasonable margin for error. Adjusting the speaker audio level to match the mic input via the Baofeng audio control was very tricky due to the sensitivity of the soundcard. The Baofeng radios are not very good at providing this low signal level because the only audio output on the radio is intended to drive a speaker with audio levels of a volt or two. As a result, the received signal level going to the soundcard had to be very low (of the order of a few 10's of mV). The USB soundcard I have only provides a microphone input and not a line-level input. My laptop soundcard doesn't work very well, so I wanted to use a cheap USB soundcard. I had two problems when trying to set up the radio/soundcard interface. This includes packet radio using the direwolf TNC as well as newer and more efficient protocols such as ARDOP. I was interested in using a couple of Baofeng UV5R radios for VHF/UHF digital amateur radio communication.
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