TopBand: Tnx for Shunt feed info

[leewells@lexmark.com]

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


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