[TowerTalk] Re: Welcome to towertalk

Steve Miller millersg@dmapub.dma.org
Wed, 20 Oct 1999 11:03:28 -0400 (EDT)

It seems that either method would work.

How much additional gain can you achieve compared to the max. F/B tuning? 

I'm not too familiar with tweaking Quads, but adding 5 sets of relays or 
5 remote variable capacitors seems like a lot of additional complexity for
only an extra dB or so of gain. Reliability would also suffer. I would be 
inclined touse a single tuning that compromises between gain and pattern 
and not hassle with the additional components and control lines.

Computer models are not accurate enough to realize 90 dB null designs. 
Also, models of the antenna environment are usually a very simple (poor) 
approximation that produces a larger error. I always look at the peak 
sidelobe levels when evaluating an antenna patterns. This is more useful 
when operating and the models predict sidelobes more accurately than nulls.


> Has anyone ever added a stub to a 2 element quad relector that was adjusted 
> to best F/B with a relay across it that tuned it for maximum gain?  Or 
> installing a variable capacitor with the tuning shaft extended to the boom 
> and a selsyn motor to tune it for gain for F/B?  I was planning to try both 
> of these on a 5 band 2 element quad.  
>      I had a 5 band 2 element quad, same spacing, with the DE's tied together 
> and it destroys the patterns and a great antenna.  I put in the computer a 5 
> band 2 element quad with tpered spacing and individuatlly driven DE's and the 
> patterns were better than a mono 2 element quad.  That's not true with 
> multi-band yagi's.  Then I came up with a way to improve it even more.  I've 
> got a mono 2 element quad with a yagi director in the computer that gives a 
> 90 db null in the rear.  Awesome!  That's the largest I've ever obtained.   

Steve Miller   N8SM   millersg@dma.org   http://www.dma.org/~millersg

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