- The power out pin on the Baofeng interface couldn't power the external circuit. I didn't supply enough amps.
- Whenever the external VOX circuit keyed the radio, it quit working all together. It turns out that the RF coming out of the radio is interfering with the external VOX circuit. Which, I did not shield. I'll be adding a shield and trying again.
In the meantime, I did get on APRS for the first time using the little circuit, using the internal VOX of the radio. It wasn't ideal, but it worked.