Dink,
You might try your idea of hanging some wire to "lengthening" the boom, but
the approach I would consider is the technique of removing guy wire
resonance by breaking them up with insulators. Break the boom up using
Fiberglass tubing or solid material. Remember you can sleeve tubing together
to
effectively increase the wall thickness. I will add a little weight to the
boom, but it will be very strong. You may have to have some pieces machined
to achieve a tight fit. There are readily available sizes up to 2 in OD,
larger sizes may be a little more difficult, but either PVC or Aluminum may
be used as a filler to accommodate the boom diameter.
Regards,
Norm W4QN
=======================
Message: 4
Date: Mon, 30 Nov 2009 14:45:24 -0800
From: mwdink <mwdink@clearwire.net>
Subject: [TowerTalk] Electrically lengthening a boom
I have a 40M beam underneath a tribander with about 8 feet of
separation. The tribander is on the mast and
the 40M beam is on a Tic Ring so both can be rotated independently. All
is well as long as both booms are aligned.
Once the the two start getting a few degrees (~30) out of alignment,
the SWR on 20M starts rising until I get to
90 degrees (3.3:1) then starts going down again until I reach 180
degrees. Yes, the boom of the 40M beam is
darn close to resonant on 20M as it's about 32 feet long. (15M and 10M
are unaffected) I've put up with this
for a couple years because I really don't want to bring that 40M monster
(to me) down.
So, I was investigating detuning the boom (all the elements are isolated
from it) when I came up with another
possible idea for electrically lengthening it. Why can't I...
1) drill a small hole in the boom
2) insert some stiff wire (or even tubing) inside the boom and push it
through until it comes out one end
3) electrically connect the wire to the boom where it goes through the
hole.
Wouldn't that make my boom longer as far as the 20M elements of the
tribander are concerned? I wouldn't think I would have to go too far out
the end
of the boom.
Even if the wire hangs down a bit off the end that shouldn't be an issue.
Suggestions?
cheers
dink, n7wa
------------------------------
Message: 6
Date: Mon, 30 Nov 2009 13:06:39 -0800
From: Michael Dinkelman <mwdink@clearwire.net>
Subject: [TowerTalk] Electrically lengthening a boom
To: Towertalk <towertalk@contesting.com>
Message-ID: <4B1433DF.7040202@arrl.net>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
I have a 40M beam underneath a tribander with about 8 feet of
separation. The tribander is on the mast and
the 40M beam is on a Tic Ring so both can be rotated independently. All
is well as long as both booms are aligned.
Once the the two start getting a few degrees (~30) out of alignment,
the SWR on 20M starts rising until I get to
90 degrees (3.3:1) then starts going down again until I reach 180
degrees. Yes, the boom of the 40M beam is
darn close to resonant on 20M as it's about 32 feet long. (15M and 10M
are unaffected) I've put up with this
for a couple years because I really don't want to bring that 40M monster
(to me) down.
So, I was investigating detuning the boom (all the elements are isolated
from it) when I came up with another possible idea for electrically
lengthening it. Why can't I...
1) drill a small hole in the boom
2) insert some stiff wire (or even tubing) inside the boom and push it
through until it comes out one end
3) electrically connect the wire to the boom where it goes through the
hole.
Wouldn't that make my boom longer as far as the 20M elements of the
tribander are concerned? I wouldn't think I would have to go too far out
the end
of the boom. Even if the wire hangs down a bit off the end that shouldn't
be an issue.
Suggestions?
cheers
dink, n7wa
------------------------------
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