On 9/3/13 11:19 AM, john@kk9a.com wrote:
If my model is correct, changing the phase of one yagi 20 degrees makes
very little difference in the gain or pattern.
At most, I'd expect a null to move a big, or change depth.
If the Yagis were, say, 1/4 wavelength apart, a 20 degree phase shift
moves the "boresight" asin(20/90) = 13 degrees. But since the yagi
pattern and the ground reflection dominates the overall pattern, you're
not going to see a huge difference in "elevation angle of max gain"
If the antennas were far enough apart so that two point sources would
have a null if spaced that far apart then that null would show up, and
would move with phase shift. For an extreme example.. imagine two
dipoles fed out of phase (W8JK array pointing vertically). There's a
null broadside to the pair of dipoles. (this is what the Both Out of
Phase/BOP position is). So that puts a fairly sharp null at the horizon
(if the antennas are otherwise phased together). If they're not
phased.. say they're 20 degrees apart, and the antennas are stacked 1/4
wave apart, the null is aimed 13 degrees up or down. Flipping the phase
moves the null.
John KK9A
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Method of calculating phase delay variation
when
stacking two dissimilar yagi antennas?
From: Jim Lux <jimlux@earthlink.net>
Date: Sun, 01 Sep 2013 10:22:23 -0700
Here's the deal..
For phased arrays you can have fairly large phasing errors and the *gain*
doesn't change much. What changes is the depth and position of the nulls.
So the whole deal on the BIPBOPTOPBOT thing is that you're moving the
nulls around to suppress the stations you don't want to hear, while
slightly changing the gain in the directions of the stations you DO want
to hear. (for that matter, most likely, what you're doing is moving the
null OFF of the desired station).
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