[TowerTalk] Stacked Yagis
Tue, 20 Oct 1998 17:39:29 -0600
Bill, That makes sense to me!
Bill Hider, N3RR wrote:
> This is documented in Dave's book in chapter 10, pages 10-1 thru 10-8. A stack
> on the top of a hill runs the risk that the upper antenna (and even the lower
> antenna) is/are mounted too high and the "figure 10-3" effect takes over. That
> is, the higher angle nulls cancel out the effect the stack would otherwise have
> over flat ground. The slope of the hill really has an effect here, and I am
> giving an exaggerated description of what's in his book, but it's easy to see
> that, on a hilltop, you have to be VERY careful how high you put your antennas
> and whether you need a stack at all.
> For those who don't know, the book is: Physical design of Yagi Antennas by David
> B. Leeson, W6QHS (now W6NL).
> Bill, N3RR
> Bill Fisher, W4AN wrote:
> > >I forgot to tell you that I have a single KT-34a that is on an 89 foot
> > >self-supporting crank up tower. I have at times put in a coax switch that
> > >allows A/B testing. When I am working a European pileup in the middle of an
> > >opening, I will typically see about 10 dB in favor of the stack. When the
> > band
> > >is just starting to open or close, I will see as much as 30 dB difference in
> > >both rcv and tx. That is due entirely to the very low angle which is
> > similar
> > >to a single yagi on a very high hill like you mentioned.
> > Very interesting Mike.
> > So far at my place I have not seen such dramatic differences between a
> > single yagi at any height as compared with any other antenna or stack of
> > antennas. My station is located on a very steep hilltop, and this is
> > probably the reason I don't see the differnce. In Terrain Analyzer, I can
> > take a 40 meter beam anywhere from 60' to 120' and see very little
> > difference in the forward lobe produced. W6NL (W6QHS) asked me the other
> > day if I thought my stacks were worthwhile on the hilltop. Mostly, I think
> > they make very little difference. I think Dave already knew this... he has
> > no stacks.... he is VERY loud.
> > 73
> > Bill - W4AN - K4AAA
> > Bill Fisher, W4AN (EX KM9P)
> > http://www.contesting.com
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