RE: Suggestion shorting and opening feedline is a good noise coupling test.
> Actually this is not true. A non-shunt fed vertical
> (i.e. ungrounded) only needs a few pf to ground to
> initiate re-radiation. only one foot of coax connected
> to the vertical will cause it to make it mess up other
> local RX antennas.
You could have a critical length of cable and antenna and have a short or
open reduce current in a TX vertical to the point where coupling is nil.
As an example, my four square couples to RX antennas a few hundred feet away
that point towards it. F/B of RX antennas pointed towards the 4 square are
quite obviously reduced by the four square. But I have to use a special
situation of a series-fed element, 1/4 wl feedlines, and shorting the ends
of those feedlines to eliminate the problem.
If it was a random length feedline or a shunt fed element, or if the element
was not 1/4 wl long, it would require a different feedline length. My 200ft
series fed tower requires about 35 feet of shorted cable to detune, when
connected to the matching network.
Obviously we can detune a tower (even a shunt feed) with feedline attached
if the feedline had low enough loss, but it almost certainly isn't a matter
of just opening and shorting the feeder in the house to do any sort of
meaningful test for interaction!! There are some combinations that would
work, but many more combinations that would NOT work.
73 Tom
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