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Author Topic: RV OCF or Dipole  (Read 189 times)
N3BUD
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Posts: 2




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« on: December 08, 2017, 10:16:46 AM »

I am considering building a multi band OCF dipole or dipole out of some old four conductor rotor ribbon wire I have.  I would like to build something that does not require a tuner.  At first I was thinking of a dipole type with the longest leg being 33 feet on each side for 40 and the smallest being 13 on each side for 17.   Then I thought of perhaps individual OCFs sharing a 4 to balun.  This should provided a wider swr spread and allow each band to be tuned individually.  IF anyone has tried using this ribbon wire for an antenna such as this I'd like to hear from you.   
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WB6BYU
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Posts: 17192




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« Reply #1 on: December 08, 2017, 12:39:29 PM »

I've done some modeling of even just 2 OCFDs on a common feedpoint,
and it doesn't work very well unless the lengths are chosen very carefully.

When you one leg of a parallel antenna happens to be close to 1/4 wavelength,
more current will flow in that leg than the OCFD leg in parallel with it.  That
throws the tuning off.


My experience with close-spaced wire such as ribbon cable is that there is
a lot of coupling between the elements that makes tuning more difficult.
Not that it can't be done, but it will take a lot of iterations.

I've had very good luck with multiple dipoles on a common feedpoint when
I use separate wires for each band and tie them off to different support points,
so the ends of the wires are more separated from a he other wires.  Letting
the last few feet of each wire hang down from the bundle will help somewhat
if that isn't an option.
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