[TowerTalk] QEX article - got it

[Robert Chudek - K0RC]

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 at aol.com
Subject: Re: [TowerTalk] QEX article - got it
To: garyschafer at comcast.net, towertalk at contesting.com, WA6RKN at arrl.net
Message-ID: <c44.284f2562.36e830a2 at 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 at 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