I agree, window line changes when wet. But my measurements indicate it
is the velocity factor that changes. Thus the electrical length of the
line changes from dry to wet, etc. In a 100 ft length of new window
line, from dry to wet and then with a wetting agent, with the line
correctly terminated into its characteristic impedance, the loss
measurement or changes were almost not perceivable. ( Less than 0.1
dB, 2 - 30 MHz).
In the case of the original G5RV, the design specified 34 ft of OPEN
WIRE line as a matching section on 20M. The open wire line is much much
less affected by water, rain, ice, snow and dirt. It is specifically
1/2 electrical wavelength on 20M. If one uses window line, as in my
tests, the electrical length will change from dry to wet, due to VF
change, and thus the matching section of the line will no longer be
electrically correct. Thus the ATU must be adjusted to account for the
change in electrical length. So if you are using window line, one
should expect the ATU to be required to change values as the weather
changes.
Also with the G5RV, there is a 1:1 balun at the point where the balanced
line transitions to coax. Again researching the original documentation
for the G5RV, the coax line should be 75 ohm coax. The feed point of
the G5RV is ~ 90 ohms +/-j0.
73
Bob, K4TAX
REF: G5RV_w5rh.pdf
--
Retirement: It's nice to get out of the rat race, but you have to learn
to get along with less cheese.
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