There have been numerous reports about Raspberry Pis crashing when using the WsprryPi software. My Raspberry Pi Zero was no exception when feeding the magnetic loop antenna. These crashes usually happen right at the beginning of a transmit cycle and network connectivity is completely lost so the Pi needs a hard reset. Oddly on some days the system crashed all the time and on other days it worked like a charm. I found the source for these crashes thanks to someone on the WsprryPi issue tracker suggesting RFI (Radio Frequency Interference) as one possible cause for this problem:

With the Pi mounted almost in the centre of the loop, the power cable that connects it to the powerbank was sometimes dangling too close (less  than 10cm) to the bottom of the loop and the capacitor. As this is the "hot" part of the loop with fairly high electric fields, RF was creeping in the lead leading to these crashes.

Keeping the cable away from the loop solved the problem. And maybe it's not a bad idea to put a ferrite choke on the cable.

72/73 for today, Mark