[NLRS] choke balun question

[Dr. Gerald N. Johnson, electrical engineer]

Yah, sure, it works with and without a balun or choke. Can you tell the
difference? Maybe.

The balun/choke will reduce RF on the outside of the coax and so cut
down on the more or less omnidirectional vertically polarized signal.
That discriminates against moderately distant signals with vertical
antennas and probably local noise that seems to be more predominantly
vertically polarized. And means the fades on long distance signals will
be deeper. Some of those fades I've found (with a pair of cross
polarized antennas) to be polarization shifts, so as they dip on the
horizontal they are just coming up on the vertical.

If all you work are horizontally polarized signals, you may occasionally
detect an improvement in signal to noise (not necessarily absolute
signal strength) on signals that have true horizontal polarization when
they reach you.

For general hamming, I'd not bother with the choke or balun. The added
sensitivity to vertical polarization may or may not help in random
contacts, though its likely to be at a high angle of radiation,
providing the antenna is up more than a half wavelength above ground.

To make a choke, coil up about a quarter wave of coax at mid band, say
at sqrt (14 * 28) = 20 MHz. 11 or 12 feet. Its not critical. Coil
diameter should be less than 3 feet (cause that's only one turn) and
greater than 6" for R-8 (else the center conductor could migrate over
time and cause a short), smaller diameter for R-8X.

A gang of ferrite toroids on a straight piece of coax (a current balun,
invented long since CC made the A-3) works too and is more compact. I'm
of the opinion that wadding the coax up is as effective as a coil, just
so long as the coax goes in multiple directions in that lump and is
about a quarter wave long at mid band.

73, Jerry, K0CQ

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Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
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