[Elecraft] Tuner bug

[Andy Durbin]

My top band antenna is an OCF wire running round my back yard wall at about 5 ft above ground.  It has been through a number of iterations to make it tunable on 160 and to handle 500 W.

500 W capability was achieved with a home brew feed point L match consisting of a large air-spaced variable capacitor and an inductor wound on PVC pipe.  It worked fine until the small hours of Saturday morning when the SWR jumped to a really high value and tripped my KPA500 reflected power monitor.   Some quick tests showed it worked fine up to about 200 W but anything over that gave an instant transition from low SWR to very high SWR.  All easily seen in my station controller's data log.   It seemed likely there was an insulation breakdown somewhere, but where?

Careful inspection of the air-spaced variable revealed a small bug between the plates.  It was carefully extracted and viewed under the microscope.  It was well charred!

Quick check on 160 m and the antenna will handle 500 W again.  Now ready to try for a few missing states in ARRL Sweep Stakes.

Not all bugs are neatly categorized as either hardware or software.

73,
Andy, k3wyc