----- Original Message -----
From: "Jim Brown" <jim@audiosystemsgroup.com>
To: <topband@contesting.com>
Sent: Wednesday, April 23, 2014 1:05 PM
Subject: Re: Topband: Suggestions for a tower?
On 4/23/2014 5:15 AM, Jaan Jürgenson wrote:
I could think of isolating the guy wires or replace them for
non-conductive
type. I'm not sure if it possible to isolate the base today. Shunt fed the
tower, use it as a folded monopole? Or should I just use the tower as a
support for a L-antenna?
Hi Jaan,
Certainly the tower without the guy wires would load and perform quite
well, but it also needs a good radial system.
To load the tower, you would need to isolate those guy wires, and also
break them up with egg insulators. That's a tricky thing to do safely
with the tower already up in the air, and it means that you will have to
REPLACE the existing guys, because they will not be long enough to
terminate at each insulator. I would get advice from someone very
experienced with tower work before attempting it.
Another way to use the tower effectively is as a support for a sloping
vertical that is insulated from the tower at the top, and fed from the
base, also with radials. The tower will act as a passive reflector,
providing a few dB of gain in the direction of the slope. The tower also
needs radials for this configuration. I have two sloping wires like this
on my 120 ft tower, one going east, the other west. The feedpoints are
roughly 18m from the tower.
You MIGHT get away with the sloping wires with the guys in place as they
are -- I would certainly prepare and study an NEC model before trying it.
73, Jim K9YC
With a 137' tower you can also start the shunt feed at 10-20' above ground
and run elevated radials for high efficiency.
Carl
KM1H
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