[TowerTalk] Concentric Masts

[john at kk9a.com]

I have never seen a set up like this, however I see no reason that it would 
not work well.  There may be some interaction with your tribander depending 
on the antenna orientation, however the 10' spacing should help minimize 
this.  I'm assuming from your description that you have a bearing on the top 
of the outer mast for the inner one.  You don't say why a TIC ring would not 
work.   They fit my Rohn 65G and I think that TIC makes an even large model 
so if it doesn't fit, you must have a huge commercial tower or someother 
factor.

John KK9A


To: TowerTalk <towertalk at contesting.com>,CADXA <CADXA at LISTSERV.TEMPE.GOV>
Subject: [TowerTalk] Concentric Masts
From: David Gilbert <xdavid at cis-broadband.com>
Date: Wed, 20 Dec 2006 21:15:24 -0700
List-post: <mailto:towertalk at contesting.com>

I'm going to be limited to one freestanding tower at this QTH, but I'd
like to be able to operate two stations simultaneously (with appropriate
filters) for when friends visit.  I expect to put a 40m yagi about 10
feet above a decent tribander and would like to be able to point them
independently.   TICs won't fit the tower, and side mounts won't give me
full azimuth.  Has anyone ever tried to use concentric masts, such as a
longer 2 inch mast inside a shorter 3 inch mast, driven by two different
rotators?  A sketch of the concept can be found at
www.stone-ridge-road.com/ab7e.  It seems simple enough that I'm sure
others have tried it and I'm curious what issues they might have had
with it (coax loops getting tangled, etc).  The rotator for the 3 inch
mast might even fit inside the tower.  The idea doesn't look like it
would cost much extra to implement, aside from the second rotator and
mast of course.

Thanks in advance for any comments.

73,
Dave   AB7E