nuckolls.bob(at)aeroelect
Guest
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 Posted: Fri May 21, 2010 5:19 am Post subject: Terminating Coax Cable to VOR Antenna |
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At 07:41 AM 5/21/2010, you wrote:
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For frequencies near or above 1 MHz, coaxial cables are best
terminated with a connection method that is easy to make or buy that
avoids the unnecessary losses in pigtailing the shield.
Yes, you can "get away with" pigtails, but Google "Kimmel Gerke
pigtails" and learn how to do this important task....
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In this case, we're making a transition between a coaxial
feed line and pieces of metal intended to be exceedingly
NON-coaxial, I.e. elements of an antenna.
Pig-tails on the end of the coax simply become part
of the total length of each antenna element. The
existence or non-existence of a constant impedance
connector at the end of the coax is not a factor
for over-all performance. The technically elegant
design will shorten the elements by the same dimension
added by the pigtails. This adjustment for length
will produce a more satisfying SWR plot over the
range of interest . . . but it's not going to
make an observable difference in system performance.
In this instance, doing the PIDG-on-pig-tails
termination provides a more robust, lower parts-
count transition between the feed line and the
antenna elements without degrading performance.
If one opted for a pristine connector, then
a mating connector needs to be part of the
antenna assembly. The same pig-tails from
the mating connector to each antenna element
will exist and have the same influence on the
antenna's resonant frequency. Parts count and
numbers of connections go up.
The K&G admonitions for preserving feed-line
integrity are quite accurate but not applicable
in this instance.
Bob . . .
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