Topband: Phased "Flags"

[Tom Rauch]

> The broadside configuration was selected for the good null off the side of
> the pattern. 315 foot spacing was used because of the plots presented in
> K6SE's QST article. After a lot of testing, it appears that 315 feet might
> be too wide to achieve the performance I want. The front lobe seems
> narrower and the side nulls don't seem to be as deep as I hoped for. Since
> I still don't have my modeling capability back, I wonder if anyone has
> played with the spacing on these ground independent RX antennas and has
> any suggestions. I still have time to change the spacing once before the
> Stew Perry run, but don't want to guess.

Remember it's a three dimensional problem. Wider spacing moves 
the nulls up off the ground and makes them more useful for distant 
noise.

1/2 wl spacing is will actually give you less of a null directly off the 
sides and make the null narrower for sky-wave signals.

Assuming your noise is mostly sky-wave, you give up S/N 
advantage pretty quick as spacing gets to 1/2 wl (and especially 
anything narrower). If the noise is groundwave, very far from the 
antenna (a few thousand feet or more), and directly off the sides 
1/2 wl spacing may be useful.

I use 330 ft or more on most broadside arrays. With sky-wave 
noise, there is a big advantage that is clearly heard when I 
compare two antennas at 1/2 wl and two at 330 ft spacing. Maybe 
you should use the wide spacing and get a phase shift system that 
lets you steer the main lobe.

73, Tom W8JI
w8ji@contesting.com


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