Of course, if you don’t put anything in your profile, and you don’t mention it, we have no means of knowing just how much you or anyone knows, so we have to assume that it’s little or nothing until we know differently.
Now that is weird. I’d never have suspected that. The RFM69CW is not (unless you changed it) working at max power, yet the ‘bad’ antenna (does the good one still transmit to the emonPi?) must be mismatched to the extent that the power drawn by RFM is enough to hit the current limit on the a.c. supply, which causes the voltage to collapse and then the processor restarts as the current falls and the voltage recovers.
What’s happening there is, as it restarts, it goes through the setup procedure - reading setting from EEPROM, setting the I/O ports, etc, then it fires up the radio and sends a test transmission. But by the time it’s got down to 8, the extra current has drained the reservoir capacitor and the voltage collapses. We can’t take more current because it puts too big a dent in the voltage you’re trying to measure.
Definitely time for an email to The Shop: [email protected] and link to this topic.