Jeffrey Herman wrote:
Hi Cecil,
It seems like it's been a decade since we debated on RRAP. I hope all is
well with you.

Things are terrible. I can't dunk a basketball anymore. :-)
Good to hear from you.

For a balun, I'm considering N4UJW's "Ugly Balun"
(see http://www.hamuniverse.com/balun.html).
UJW leaves the diameter of the coil form to the reader, only specifying that
18-21 feet of coax be used. Can you (or anyone else on RRAA) tell me if there
is an optimum diameter, considering that most of my operations will be on 20m?

This subject was recently beat to death over on QRZ.com or
eHam.net, I can't remember which. Here's some actual
measurements showing how the choking impedance varies
with frequency:

http://www.k1ttt.net/technote/airbalun.html

An ugly balun (N turns of coax) will not cover a 10:1
frequency range very well. If it performs well on 10m,
it doesn't have very much choking impedance on 80m. If
it performs well on 80m, it will have reached its series
resonant low impedance point before it reaches 10m. An
ugly balun performs reasonably well over a 3:1 frequency
range. And the choking problem worsens considerably with
non-resonant antenna systems.

However, the necessary choking impedance is minimized
if the antenna is low impedance resonant as yours will
be. I made some measurements on 20 turns of coax on a
2 liter pop bottle. It was parallel resonant at 14 MHz
(good high impedance) and series resonant at 28 MHz
(bad low impedance). It would probably function pretty
well from 40m to 15m.

A toroidal 1:1 choke-balun is much more broadbanded than
an ugly balun. For your antenna, ten turns of RG-400 on
a FT-240-61 toroid would, like mine, be good enough.
The AB-240-kit contains that toroid and comes with
instructions for winding a 1:1 choke-balun, all for $9.
However, I would not recommend that balun for non-
resonant antenna systems where three of those toroids
stacked would be about right. That web page is at:

http://www.amidoncorp.com/aai_cost_experimenter.htm
--
73, Cecil http://www.w5dxp.com