I direct feed my tower against a sloping radial which works extremely well
for me.
The highest antenna is at 45m and further down are more monobanders, most
side mounted.
I do not need any capacitor or coil to tune out reactances and the SWR2 band
with is 120kHz, SWR1.15 at 1870kHz.
73
Peter, DJ7WW
-----Original Message-----
From: topband-bounces@contesting.com [mailto:topband-bounces@contesting.com]
On Behalf Of Price Smith
Sent: Donnerstag, 15. Dezember 2011 19:17
To: 'W2RU - Bud Hippisley'; 'John Harden'
Cc: topband@contesting.com
Subject: Re: Topband: Shunt fed tower
Construction: My local ACE hardware store stocks 8-foot lengths of angle
aluminum, which is what I used for my horizontal tap rod. Their
heaviest-duty stock is more than strong enough to support itself plus the
top of my gamma rod. I don't support the weight of the entire rod -- which
consists of stepped diameters of plumbing tubing -- that way - I simply
"steady" the top portion while making electrical connection to the tower at
the tap point. (The nearest Lowe's has even heavier aluminum stock, but if
you're using wire instead of heavy tubing, the ACE stock is plenty strong
enough.) The bottom of my gamma rod sits on a single piece of 2x8
pressure-treated lumber from the scrap bin. I use a couple of scrap lengths
of 1x2 furring strips between one face of the tower and the gamma rod to
maintain spacing along the length of the rod. It ain't pretty, but it
works...I apologize to no one about my signal on 160!
Bud, W2RU
>From W0RI:
Aluminum and Galvanized Steel will set up Galvanic action in time. Those
metals DO NOT mix well. You will end up with a battery in time.
I have been shunt-feeding my 80 ft of Rohn 45 tower with monobanders for 20,
15 and 10 meters at 80, 90 and 100 ft for over 20 years.
For the shunt rod, I use common thin wall 1/2" EMT. I put a 90 degree bend
in the top piece at about 5ft from the end, I take a short piece of tubing
wrapped with 400 grit sand paper and lightly sand the tower.
I coat the rod and the tower with Penetrox and clamp the rod on with
stainless hose clamps. My tap is at 35ft and the rod is 30 inches from the
tower. I couple the EMT together with standard compression couplers. Coat
the rod and the
coupling also with Penetrox. I used some RTV on the top side of the
couplings. At the base I drove a 1 1/2 dia piece of PVC into the ground and
I use black tye-wraps to secure the rod to the PVC pipe. Put a cap on the
end of the PVC to prevent water from entering. I use an Omega match with two
500pf Vacuum variables in a 18 x 18 x 6 inch Hammon steel water proof box.
It is U-Bolted to the tower about 1 ft from the ground.
The rod is connected to the bottom of the box with a large ceramic feed
through insulator, using 1 inch braid. At three places I use short pieces of
1/2 inch PVC tubing to stabilize the rod. Use black tye-wraps on the tower
and the
rod.
The 2:1 band with is ~40kHZ. This is enough for me as I operate 99% CW. The
center freq is 1830 with a VSWR of 1 to 1. Outside of that freq I can use a
NYE MBV-V tuner.
I have drawings and an explanation which I will email if anyone wants. Just
let me know.
73......Price W0RI
_______________________________________________
UR RST IS ... ... ..9 QSB QSB - hw? BK
_______________________________________________
UR RST IS ... ... ..9 QSB QSB - hw? BK
|