[Elecraft] Efficiency of MFJ remotely-tuned loop antennas

[Andy Durbin]

"I wonder if the SWR runaway at 150W could be due to the PVC pipe used as
the insulator for the variable capacitor?  PVC is quite lossy at RF.
Perhaps when it gets hot it detunes the capacitor.  It would be easy to
check by simply feeling the cap to see if it gets warm."

The insulator/dielectric is PEX not PVC.   I have studied the impact of temperature on the antenna and it exhibits some interesting and sometimes non-intuitive effects.  The biggest change is seen when the sun hits the antenna soon after run rise.   Study of heating during TX would require sensitive thermal imaging.  There is no change detectable by touch after a TX.  Touching it while transmitting would be counter productive and perhaps painful.

I have lots of notes and some plots of the thermal characteristics.  Maybe I'll get back to working on it one day.

73,
Andy, k3wyc