On 11/15/01 11:07 PM, Tom Anderson at ww5l@gte.net wrote:
>I've got a Mosley Classic 33 WARC and they recommend an 8 inch diameter
>coil of RG8 for that antenna, 10 inch if you use the 40m kit on the ends
>of the driven element.
How many turns?
One problem with a coaxial balun is you don't want too many turns. You
have to have enough turns to give sufficient inductive reactance at the
lowest frequency, but too many turns actually makes the balun ineffective
at higher frequencies.
Back in 1995, Ed Gilbert posted a great message about actual measurements
of air-core coaxial baluns, which is referenced here:
<http://www.k1ttt.net/technote/airbalun.html>
One of Ed's conclusions:
- Don't use too many turns. For example, the HyGain manuals for my 10
and 15 meter yagis both recommend 12 turns 6 inches in diameter. At
the very least this is about 3 times as much coax as is needed, and
these dimensions actually give less than the desired choking impedance
on 10 and 15 meters.
--
6-7 turns on a 4-inch PVC makes a great balun for 20-10m, and 12 turns on
a 4-inch PVC works from 40-10m, assuming a 50ohm feedpoint.
Bill Coleman, AA4LR, PP-ASEL Mail: aa4lr@arrl.net
Quote: "Not within a thousand years will man ever fly!"
-- Wilbur Wright, 1901
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