----- Original Message -----
From: "Bill Tippett" <btippett@alum.mit.edu>
To: <towertalk@contesting.com>
Cc: <n6bv@arrl.org>
Sent: Tuesday, July 13, 2004 4:13 AM
Subject: Re: [TowerTalk] Stacking Distance for M2'd 6m7JHV?
> W6RMK wrote:
> > It might be interesting to trade that scheme (which has 4 possible
> > settings) against a scheme where you combine the two antennas with
> > 0,90,180, or 270 degrees phase shift between them, which also has 4
> > settings.
>
>
> W5WVO wrote:>But how to model the
> effect of various phase shifts on take-off angle? Does anyone have a
handle on
> that? I don't know of any software that is set up to do the math involved
in
> this scenario. Any ideas or recommendations?
>
> HFTA will handle 0 and 180 degrees, but not 90 and 270. From
> what I recall when playing around with various phasing combinations using
> Eznec, 0 and 180 are really the most useful cases anyway. N6BV might
> want to comment so I'm copying him on this.
>
> 73, Bill W4ZV
This may be true for HF antennas, but when you get to VHF and UHF, it might
not be the case. Rarely, in an HF situation, would you have the antennas
many wavelengths apart. In the VHF (and particularly UHF) world, this isn't
so hard, so you would have a lot of very narrow grating lobes. The
discussion of finding optimum elevation angles for Es or F2 propagation, for
instance, makes me think that you might want a bit more flexibility. I'm
not sure that at UHF and up, though, it's such a big deal. There's probably
other effects that start to dominate (diffraction, etc., from the terrain)
There's also the issue of having both antennas working all the time (as
opposed to on HF, where the sky noise makes this less important).
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