>At 12:16 PM 2/15/2009, you wrote:
>>
>>I just wonder what would I gain by changing to a full length 1/4 wave wire.
>>WB5OXQ
Jim,
I tried e-mailing you directly, but it bounced. So, I'm posting to the group.
I used one of these to very good effect for over eight years on a 60
foot tower with the FP at 55 feet.
The coil inductance is high enough to serve as a trap on 40M and as a
loading coil on 160M. The enamel coating on the small-gauge wire
they use for the coil is subject to degradation due to weather and
the effects of UV radiation, meaning that the turns will eventually
short together. I made my own bigger and better coil to (A) mitigate
the effects of weather and sunlight, and (B) reduce losses. If I
remember correctly, the coil inductance is about 125
micro-Henries. My HB coil was made of #12 solid wire, 5" diameter
and about 13 inches long, 4 TPI, would around 6 grooved plexiglass
ribs that I painstakingly made myself. Very labor intensive, and
very well worth the effort. That antenna works very well for what it
is. It allowed my to get out a good low band signal from a small 100
x 125 foot lot.
The problem with removing the coil and extending the length of that
leg is that (A) you will lose 40M , like you already mentioned, and
(B) with only 50 feet of FP height you will end up with a lot of
"extra" wire to find a place for. Folding the extra back on itself
(a al linear loading) will increase your losses as compared to using
a better-constructed, higher-Q coil, and laying it all out straight
will introduce more horizontal radiation, and require a larger
"footprint". The twin sloper relies on its vertical polarization to
put out a good low angle signal for DX work.
I found fabricating a better coil a big advantage, but I can't see
any real advantage to loosing the coil.
Hope this helps, YMMV
Charles - K5ZK
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