[Antennas] Mult-band Quads- Matching

[NPAlex at aol.com]

I would like to add some comment regarding mult-band Cubical Quad matching  
based on some of my experience.  Historically there have been basically two 
 approaches, one was parallel all driven elements and feed them with coax 
or  balanced line and use an antenna tuner.  Or individual feeds for each 
band  switched with a remote antenna switch.  The problem to be resolved is the 
 variation in source impedance from band to band with a constant element  
spacing.  The impedance ranges from near 50 ohms (typically 20m) to over  100 
ohm for 10 meters.  
 
The "Spider" designed quads purports to solve this problem by distributed  
spacing (optimum for each band) and therefore each now is 50 ohms.  Not  
achieved in my analysis of this form, and I believe there is more interaction  
when the elements are distributed versus co-located ( I think LB Cebik also  
concluded this).  
 
So what is the solution to single feed of a multi-band quad?    Lightning 
Bolt (SK), Gem (SK?) and Cubex (alive an well) offered matching  
transformers.  The Lightning Bolt model was a two level transformer, with  Low and Hi Z 
terminals.  Cubex (still offers) a family of transformers  depending on the 
number of elements (2, 3 or 4) which offers three levels of  termination Lo, 
Mid and Hi.  One limitation is power, 1500w is the  maximum.  The matches 
are not perfect, but in general the antenna will  exhibit less than 2:1 
across each band.  
 
However, my preference is individual matching cables for each band.   
Typically 10, 12 and 15m respond well with odd quarter wave 75 ohm calbe (I  
found 3/4 wave the best choice as it allowed the remote switch to mount on the  
mast) and 1/2 w 50 ohm cables for 17m and 20m.  There is always the  
question as to how should the unused matching cables be terminated?  Open  or 
shorted?  I have done both and still have not found a consistent  position - cut 
and try.
 
Norm W4QN
 
 
Message: 1
Date: Tue, 24 Nov 2009 18:52:06 -0600
From: Wendell Wyly  - W5FL <w5fl at sbcglobal.net>
Subject: Re: [Antennas] Quad  matching
To: Tom Horton <k5iid at sbcglobal.net>
Cc:  antennas at mailman.qth.net
Message-ID:  <77FE249A-B56E-419F-961E-5E9C5B616198 at sbcglobal.net>
Content-Type:  text/plain; charset=US-ASCII; format=flowed; delsp=yes

Hi Tom.  I  have the same experience you have with the matching  
sections.  I  simply put a home-made relay box on the bottom spreader  
to switch  all  5 quad loops on the driven element and feed it with a  
single  coax up the tower.

I did get a transformer/balun from lightning bolt  quads several years  
ago, but never tried to use it and he got out of  the business!  Hope  
to get my quad back up in the air after lying  on the ground for the  
last 5 years, but not willing to try anything  different than described  
above.


On Nov 4, 2009, at 10:34  PM, Tom Horton wrote:


I have been using quads for the better  part of 50 years and I have  
always used 1/4 wl transformers of RG-11  to RG8.
Has anyone ever built a single point transformer for one? I  know  
that Cubex among others have them for sale, but was interested  in  
trying to build something to use with a single feedline for a  change.  
Any ideas or thoughts or refs?
Thanks,
Tom  K5IID


"If It Weren't For The United States Military There Would Be NO  United  
States of America ."

September 11, 2001
We can never,  never forget !
If we aren't free and alive,
absolutely nothing else  matters !


Tom Horton K5IID
Hillsboro, TX