I just wanted to say thanks and give a short summary regarding my
question about my shunt fed tower and the wide band width I'm seeing.
>From the responses I received, most felt that the wide bw is due to the tower
being almost a 1/4wv long electrically. ON4UN's book shows a very wide BW
(almost 200kHz) for a 90 degree long vertical tower (12" face I think). My
tower
with a 4' face width at the base should show a larger BW....like a large
diamater dipole.
Almost everyone suggested adding more radials. You can never have enough
right? :-)
A couple people thought the wide BW was due to execessive ground losses.
A few people said the feedlines coming off the tower at 30' is a no-no. They
should
be brought down to ground level. (I don't think I'll be able to do this
however)
One ham said he had burned the insulators on the F-12 antennas when running
1.5KW on
160 into a shunt fed tower.
One thought my gamma arm length was a bit too long. His set-up (similar tower
height
and antennas) uses a 28' tap.
So I'm planning on adding radials as I get time. I re-did the feedpoint in
something
of a more permanent fashion, and now the SWR dips at 1.5 to 1. BW is around
170 kHz.
I don't know if I had something wrong originally, or if I do now, but it bears
more
investigation. I'll look at bringing the feedlines all the way to the base of
the
tower, but I don't think I will be able to do it.
I'm fairly happy with the performance already. I played around in the ARRL 160
contest
this weekend, and was able to make about 200 Q's. I was able to work everyone
I heard
with 100 watts. Best DX was KH7R.
73
--Lee - KT4ZX
--
FAQ on WWW: http://www.contesting.com/topband.html
Submissions: topband@contesting.com
Administrative requests: topband-REQUEST@contesting.com
Problems: owner-topband@contesting.com
|