Re: [Antennas] Re: [TowerTalk] Limit to Concentric Quads or is 2MtheBad Actor?

["John Tait" <johnei7ba@eircom.net>]

And thank you Joe..  I was wondering what I had done wrong, so it's nice to 
know that you had the same result. Like you, I'll be putting the VHF/UHF 
stuff on a second tower.
   73
  John EI7BA   http://www.iol.ie/~bravo/


> Thanks, John.  Nice to hear from you again.  You're the only one to get 
> back to me on the subject.  I was pretty sure that my guess about 
> resonances was accurate, but wanted to hear the opinions and experiences 
> of others also.  I guess I'm going to have to convince my XYL to relent on 
> her objections to my putting up a second tower so I have place for the 
> V/UHFarrays.
>
> 73, Joe
>
> John Tait wrote:
>
> > I have a multiband Quad as you describe Joe. I built (but did not model)
> > concentric multielement Quads for two metres and 70cms. These behaved fb
> > until I nested them into the existing HF Quad. The results are as you
> > describe..lobes are all over the place.
> >   Vy 73
> >    John EI7BA  http://www.iol.ie/~bravo/
> >
> >
> > > I have been using six band (6-20M) concentric quads for 15 years now and
> > > tribanders for double that.  My current quad is a six bander which I
> > > modeled with EZNEC before building it.  The actual characteristics
> > > conformed quite well to the model.  (BTW, I originally modeled each band 
> > > as
> > > a monobander, sized according to the standard formulas, and imported 
> > > them
> > > to make the six bander.  There was about a 0.2 dB reduction in gain in
> > > going from monoband to six band.  I should add that I did not try to
> > > optimize the monobanders, while the six bander was optimized for maximum
> > > forward gain.) The bottom line was that there was very little compromise 
> > > in
> > > performance in going from monoband to six band.
> > >
> > > Always eager to press the envelope, I had planned on adding a 10 element
> > > 2M quagi to the six bander.  After modeling the quagi as a monobander 
> > > and
> > > optimizing it, I imported it into the six bander.  The pattern really 
> > > went
> > > to pot:  major lobes developed on the rear and the pattern was really
> > > brutalized.  Surprisingly, there was not that much change in feed
> > > impedance.  I then replaced the quagi with an optimized 2M quad, and the
> > > same thing happened.  I played with the model and found that if I slid 
> > > the
> > > 2M quad outside of the cage formed by the six band quad (in other words,
> > > so that the reflector end of the 2M boom was at the last director end of
> > > the six band boom), the original monoband pattern returned.
> > >
> > > My guess is that given the high frequency of the 2M quad, there are just
> > > too many potential harmonic resonances in the six bander's elements to
> > > interact and disrupt the performance and pattern of the 2M antenna.  If
> > > anyone has any thoughts or a similar experience, I'd be interested in
> > > hearing about it.


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