Pete Soper asks about using a pair of coax cables as a balanced line.
The signals inside these two lines don't know the difference from normal use.
Any moisture will disturb the loss and will affect velocity factor in exactly
the same way as in normal use. If water is inside one of the lines only, the
velocity factor of that line will be much lower than the other and the phase
relationship (normally 180 degrees in balanced line) will be upset, possibly
to the point of phase cancellation, resulting in no output from the line at
all!
If the two lines are from a different batch of coax, the velocity factor
could be different and you might want to measure the loss of the "balanced
system" to make sure that the signal is indeed present and 180 degrees out of
phase at the far end. This is something that really shows up at vhf/uhf due
to the shorter wavelengths.
I wonder what your application is to need a line like this as it is unusual
to see a need for a 100 or 150 ohm line?
73 de Gerald Williamson, K5GW
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