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Author Topic: Fan dipole from multi conductor cable  (Read 4143 times)
WA2WMR
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Posts: 31




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« on: August 22, 2008, 09:55:15 AM »

Has anyone ever used a multi conductor cable for a fan dipole. ie. ladder line, one side cut to 1/4 wavelength on 80 and one side cut to 1/4 wavelength on 40 (of course there would be two of these for a dipole) or three conductor electrical cable for let's say 10, 15, and 20? Fed with ladar line or fed with coax?
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K8GU
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« Reply #1 on: August 22, 2008, 11:29:34 AM »

There was an article in the ARRL Handbook or Antenna Book about 15 years ago that described a fan dipole made from 300-ohm TV twin lead.  In my experience, that's way too close together and you'll get serious interaction whening tuning up.  I usually use at least 4-6 inches of spacing between my wires.  Many people prefer 8-12 inches or more.
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KB1LKR
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Posts: 1898




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« Reply #2 on: August 23, 2008, 12:52:06 PM »

What's the interaction for a fan dipole w/ parallel, coplaner wires?

Do the wires tend to need shortening (as the shorter wire(s) should make the longer wire look fatter for at least part of its length)? Or do they need lengthening, vs. a single wire on each leg?

I also assume the longest wants to be trimmed in first then the shorter one(s), as a short wire should be less aware of what's happening far away at the end of the long wire then vice versa.
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WB6BYU
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« Reply #3 on: August 25, 2008, 12:53:00 PM »

It isn't simply a matter of longer and shorter - the
wires couple together so that changing the length of the
longer wire affects the resonant frequency of the shorter
one.  That is why trimming the longest wire first and
working down to the shorter ones is the best method, though
there may still be some interaction.  The more bands and
the close spacing between wires, the harder it is to tune.

Generally I've found the interaction to be reduced the
further the ends of the wires are separated from the other
wires. Letting a few feet of wire hang down at the end
of each element makes it a bit easier to tune.

So, yes, it can be done, but the difficulty (and frustration
level) go up rapidly with the number of different bands
you are trying to cover.
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