Barry, Ive built a few shunt feeds over the years and studied the BC band
ways of doing it.
Look at the shunt arm as a gamma rod on a yagi. It has to be of some
diameter and spacing ratio relationship to the tower itself. Anything will
work after a fashion, from a #12 wire to a 4 wire cage surrounding the
tower. The AM broadcasters use 3 and 4 wire
In my case the first attempt was with #12 and 100' of 25G with a 4PV
Christmas tree and had a 60 KHz bandwidth. At 800W The series capacitor
arced and that was with 3500V spacing.
I then used 3/4" CATV hardline secured and spaced 18" from the tower by 3/4"
PVC and T fittings. It worked very well and the Bw was 120 KHz and the
series capacitor arced at 1200W only when I was at the BW extremes and it
was raining out. The capacitors were in a box shielded from the weather but
not the moisture.
The final arrangement was a 2 wire cage of the hardline, one off each leg.
BW was now well over 200 KHz and no more arcing. I didnt want to have to
resort to vacuum variables and motor driven tuning as that takes too much
time in a contest.
There are some tower heights and shunt height/spacing that will generate
huge voltages at the feed. I dont know if anyone has compiled info on that.
I believe that my shunt rod length was 60'. The feed network was an Omega
match.
Carl
KM1H
----- Original Message -----
From: "Barry" <w2up3@verizon.net>
To: <towertalk@contesting.com>
Sent: Sunday, August 05, 2007 7:46 AM
Subject: [TowerTalk] Details on shunt feeding tower for 160?
> Hi all,
> I'm considering shunt feeding my tower for 160. Would appreciate
> details from those with similar setups who have done it successfully.
> Tower is 76 ft of Rohn 45 with a C31XR at 75 ft and a Magnum 240 at 85
> ft (and Phillystran guys.)
> Tnx,
> Barry
>
> --
>
> Barry Kutner, W2UP Newtown, PA
>
> _______________________________________________
>
>
>
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