After a couple of days of phenomenal round-the-world spots using my Raspberry Pi as a 5 mW WSPR transmitter (Wsbrry Pi) - the Pi has failed. Since it's worked reliably for over 6 months prior to connecting the GPIO output (via LPF) to a ground-mounted vertical antenna last night, I suspect either static, RF fields created by other nearby antennas, or a ground loop killed the output circuit, resulting in excessive current drain. (The 3.3 volt rail now measures < 2 ohms to ground and the regulator output is so low the Pi will not boot). I can't positively say that WSPR use caused the failure but it's my best theory, and I thought it would be worth noting for the benefit of others who may wish to give this a try.

The DPLL capability of the Pi to generate RF signals make it ideal for use as a WSPR beacon, and I think some additional buffering and galvanic isolation of the antenna will prevent failures of this kind. Any thoughts along this line would be welcome.

73, Bob W9RAN