[TowerTalk] Method of calculating phase delay variation when stacking two dissimilar yagi antennas?

[Jim Lux]

On 9/3/13 11:19 AM, john at 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 at contesting.com
> Subject:	 Re: [TowerTalk] Method of calculating phase delay variation when
> stacking two dissimilar yagi antennas?
> From:	 Jim Lux <jimlux at 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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