[TowerTalk] Quad Users

[Paul Ferguson]

 L. B. Cebik wrote:

> 5.  A 5-band common feed system will work.  Whether it provides optimal
> performance for the antenna type is exceptionally difficult to ascertain,
> since having the requisite towers and other materials to make a valid
> side-by-side test between separate and common feed antennas that are
> otherwise the "same" is not normally feasible for most hams.  However, I
> have received numerous reports of folks getting very good results.  I
> cannot say that they would or would not get "even better" results with
> separate feed due to the many variable involved.  The band that
> potentially suffers most is 10 meters, at least in theoretic studies.
> Hence, the question may come down to a decision between the convenience of
> a single feed vs. the importance of 10 meters in the overall operating
> schedule.

I owned a Lightning Bolt 2-el 5 band quad for a few years. It used a common 
feed. I thought it performed well except on 10 meters. It had front/back on 10 
but when I switched to an R-7 vertical for comparison, it was rarely better and 
sometimes worse. The other bands were almost always much better on the 
quad as you would expect. I have no lab-style measurements, but I came to 
this conclusion without the bias of knowing any work suggesting it might be 
a poor performer on 10m. 

I modelled the quad using EZNEC and found it well predicted the poor 10 
meter performance I had observed on-the-air. I experimented with my model --
changing lengths, adding separate 1/4 wave feeds to a switch box. I also 
noted that if the inactive driven elements were electrically open-loops, there 
were strong interactions. I used a switchbox that left the 1/4 wave feedlines 
open when not in use (so the inactive elements were closed-loops at their 
resonant freq.) 

I rebuilt the quad several years ago according to my model and have been 
happy with the results. I think it performs well on all bands and the 10 meter 
poor performance is no longer. Whether all this work and is worth getting 10 
meters performing well is up to you.

If you have plans to build a 2-el 5 band quad, I urge you to model it first.  

73,
K5ESW
Paul  
Paul.Ferguson@pobox.com

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