[Top] [All Lists]

[Towertalk] Shunt Fed Tower 160/80

To: <>
Subject: [Towertalk] Shunt Fed Tower 160/80
From: (WL7M)
Date: Wed, 04 Sep 2002 14:51:13 -0800
My thanks to those on the reflector whose ideas I've glommed onto over the 
years.  I finally decided to try a shunt fed tower for 80 and 160 
meters.  Having a humongous variable capacitor with huge spacing, I gave it 
a try.  I have no idea what the range is on the variable cap, but it 
works!  I almost forgot the essential "hook the coax braid to the bottom of 
the tower" step, but a recent TTer confessed to having made that mistake, 
and, I did too.  When I did that, the SWR fell right into range.  So, my 
thanks to that humble but wiser soul who passed on that bit of information.

My tower is 40 feet of Rohn 25G, with a Mosley Pro57B about 8 feet above 
it, and a Cushcraft 5 element 6 meter yagi about 8 feet atop 
that.  Apparently there is sufficient capacity hat effect to make it work 
nicely.  I attached an aluminum rod to the bottom of my Hazer that extends 
out about 30 inches.  From that, I attached a wire to run down to the 
ground.  Hooking up the cap and properly connecting the coax, I set the 
Autek Antenna analyzer to 3.535 MHz and adjusted the is barely 
meshed, and the SWR was 1.3 : 1.  Returning to the shack, I fired up the 
Icom 756Pro and it agreed.  My Alpha 87a was next - but I took the 
precaution of running it through the Palstar AT4K tuner to make sure I had 
a good match.  Worked great!

For 160 meters, the variable cap is about 1/3 meshed, and the SWR is also 
about 1.3 : 1.  That means I have to wade through 6 feet of snow in the 
winter to switch bands, but I'm sure it will be worth it!  As mentioned on 
this reflector before, if you bring the bottom of the wire toward the tower 
base, or away from it, it will affect the SWR as well.  I moved mine to 
about 2 feet from the tower base and the SWR dropped to 1.2 : 1.  I have a 
few radials attached at the tower bottom, and I'm sure I can use even 
more.  That's another project to finish before the winter sets in (which 
will be about a month from now!)

Thanks again to the TTers for all their collective ideas!  Hope to work you 
on 80 and 160 this winter!

Fritz Creek, Alaska

<Prev in Thread] Current Thread [Next in Thread>