[Elecraft] Using the K3s Tune button causes a growing SWR on my KPA500

[Andy Durbin]

Don't need to have ferrite in the antenna system to see this sort of SWR "runaway".   I have the same problem with my home brew small transmitting loop if I run over 100 W.

Spent some time trying to figure out what was heating and causing the loop's resonant frequency to shift. My preliminary analysis showed expected temperature coefficient was opposite sign to that observed.   Decided the only way to really understand the problem was thermal imaging but have not got round to that yet.

Andy, k3wyc