[Elecraft] Two KAT 500s Intermittent High SWR

[Bob McGraw]

In further reading this series of postings, two things come to my attention.

The G5RV incorporates a balun at the point where the coax connects to the balanced line. That balun may be faulty as discussed about baluns heating and the core material changing values. Hence the first half of the FT-8 QSO was good but the ATU faulted in the latter part.

My measurements on balanced window line, such as used with the G5RV, indicates the velocity factor changes with moisture on the line.  (Someone stated changed impedance. I don't find this to be correct.) With a velocity factor change, the electrical length of the line changes.  This section of line is a matching section and thus its electrical length is very important.  Yes if the VF changes, the electrical length changes, and it will require to ATU to implement a change in matching component values to resolve the desired SWR.

Candidly, I doubt there is anything wrong with the KAT500 tuners.

73

Bob, K4TAX

P.S.  For an excellent dissertation on the G5RV antenna see: g5rv_w5rh.pdf

Here we learn the length is 102 ft. or 3/2 wavelength at 14 MHz.  The 
center feed Z is ~90 ohms +/- j0.  The matching section is 34 ft of OPEN 
WIRE line which is 1/2 *electrical*wavelength to a 1:1 balun which is fed via *75 ohm*coax to the transmitter.