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:https://www.bvarc.org/pdf/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.
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