At first glance, this seems like a good April issue article! But the effect can
be seen best when the mast is offset from the center of the antennas (the
antennas are not "wind balanced").
An extreme scenario makes it easier to visualize. Take two antennas with 20
foot booms. Mount the mast 2 feet from the end of antenna 1. Mount the second
antenna the same way, on the opposite side of the mast, except the 18 feet are
offset in the opposite direction.
Looking from a side view, you have 36 feet of boom, with 4 feet overlap area at
the mast. When the booms are mounted to opposite sides of the boom, the torque
will be cancelled (more or less).
Draw this on paper, a top view looking down into the mast. Press one "lever"
and determine the directions of the torque. Now press the other "lever". The
torque will be in the opposite direction.
When an antenna is "wind balanced", there will be little or no torque when
there is a wind force. I don't have the article being referred to, so I can't
comment on how much benefit the author claims this technique will provide.
73 de Bob - KØRC in MN
The North Dakota QSO Party - Saturday, 21-Mar-2009 - details here: www.k0ln.com
Message: 4
Date: Tue, 10 Mar 2009 17:07:46 EDT
From: K7LXC@aol.com
Subject: Re: [TowerTalk] QEX article - got it
To: garyschafer@comcast.net, towertalk@contesting.com, WA6RKN@arrl.net
Message-ID: <c44.284f2562.36e830a2@aol.com>
Content-Type: text/plain; charset="US-ASCII"
In a message dated 3/10/2009 12:20:24 P.M. Pacific Daylight Time,
garyschafer@comcast.net writes:
> Maybe someone could enlighten me on how mounting a boom on
> either side of a mast cancels any torque??
I'd love to but it took Dick Weber, K5IU, (a Professional Engineer) 2
3 pages of lots of calcs, graphs and illustrations to show it. It's in
Communications Quarterly from 94 and 95.
And it's wind torque. The torque of one antenna on one side of the
mast cancels the torque of the antenna mounted on the other side of the mast.
Two identical antennas mounted on opposite sides of a mast will result in
zero mast torque.
Cheers,
Steve K7LXC
TOWER TECH
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|