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[Towertalk] Re: Quad's Do any stay up? & Separate Feeds

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Subject: [Towertalk] Re: Quad's Do any stay up? & Separate Feeds
From: k2xx@swva.net (Joe Giacobello, K2XX)
Date: Sat, 14 Dec 2002 13:59:17 -0500
I have been using quads an and off for about 25 years.  I currently have 
a six bander:  four elements on 10-20 and seven elements on six meters 
on a 24 foot boom.  The HF bands are fed via a remote Ameriton switch so 
that there are separate feeds to each driven element.  The six meter 
quad also has a separate feed.  With a four element quad, the feed 
impedance is closer to 50 ohms so that 1/4 wave coax matching 
transformers are not necessary.  However, the coax links between each of 
the remote switch terminals and its corresponding driven element should 
still be 1/4 wavelength long.  The switch end of the coax links for the 
inactive bands are left ungrounded, which effectively (electrically) 
closes the inactive driven element loops.  Frankly, I am not entirely 
clear on the theory here, but there is definitely less interband 
interaction and the behavior of the quad is less sensitive to small 
changes in relative loop separations, minor dimensional errors, etc.  (I 
have done it the other way - random length coax links and grounded 
inactive terminals - and, believe me, the differences in behavior are 
major.)  The use of 1/4 wave links has been confirmed and recommended by 
K2OB, W4RNL and EI6BA, all well known quad aficionados.  I strongly 
recommend separate feeds for a multiband quad.

As far as mechanical strength is concerned, the latest fiberglass 
spreaders are much sturdier than what used to be available in the past. 
 I get my spreaders from Lightning Bolt.  I hear Max-Gain also supplies 
high quality spreaders.  It is my understanding that the Gem quad was 
designed for Canadian winters.  It is trussed so that if there is a wet 
snow or ice build-up, the spreaders are prevented from bending and 
breaking.  Although my quad is not trussed, it has been up for 2-1/2 
years now without any problems.  I live on a hilltop and the quad is 
constantly buffeted by high winds without any ill effects. The biggest 
problem is wet snow and ice coupled with high winds.  When I know that 
kind of WX is coming, I lower the quad as close to the house rooftop as 
possible and pray that heat escaping from the house will minimize any 
heavy build-up.  So far, so good.  I have 200 lb. test fishing line that 
I plan to use to truss the quad, but I'm a hopeless procrastinator and 
will probably wait until after the next ice storm.

Generally speaking, while the quad is less sturdy and more vulnerable to 
the elements than a Yagi, it's just not that much of a problem in 
practice.  Admittedly, it's an ugly looking, 3D object up there, but a 
four element, five band quad on a single support is at least the 
equivalent of five three element, monoband Yagis.  That's tough to beat.

73, joe


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