> On the other hand, as K4SAV describes, the array of verticals has
> a null at zenith, which could help attenuate lightning static and
> NVIS QRM.
The K9AY can be "fixed" if you are willing to use additional supports
to make the loop square. The high angle response is due to the sloping
"verticals." However, given the performance of the whip 4-squares, the
effort is not justified.
> Incidentally, models of the DX Engineering array actually show
> slightly better RDF (a few tenths of a dB) at closer spacings than
> 1/4 wl (with appropriate phasing). I suspect the arrays of EWEs and
> K9AYs would be similar.
Yes, closer spacing produces better RDF for the K9AY and EQE arrays.
However, the closer spacing comes at a big cost in signal levels on
the lowest band - overall "gain" can be as little as -35 dBi which
then requires a rather stout, low noise, low IMD preamplifier or the
benefits of the array are lost in the IMD and preamplifier noise.
73,
... Joe, W4TV
> -----Original Message-----
> From: towertalk-bounces@contesting.com
> [mailto:towertalk-bounces@contesting.com] On Behalf Of Terry Conboy
> Sent: Wednesday, December 20, 2006 1:12 PM
> To: K4SAV; Joe Szeliga; Tom McAlee
> Cc: towertalk@contesting.com
> Subject: Re: [TowerTalk] K9AY loops-- phased
>
>
> I've followed with interest the discussion about phased arrays of
> K9AYs vs. 4 squares, such as the DX Engineering receiving array. I
> decided to model a few variations, and they back up K4SAV's & NI1N's
> comments pretty well. As the basis for performance comparison, I
> used the RDF (receiving directivity factor) employed by W8JI. Here
> are the results:
>
> Antenna RDF, dB
> ========================
> Whip 4.7
> K9AY 7.3
> EWE 7.4
>
> 4Sq Whips 90* 10.1
> 4Sq K9AY 90* 10.2
> 4Sq EWE 90* 10.2
>
> 4Sq Whips 120* 11.6
> 4Sq K9AY 120* 11.4
> 4Sq EWE 120* 11.4
>
> 1 wl Echelon-Bev 11.5
> 1.5 wl Beverage 11.6
>
> [The 4 squares all use 1/4 wl spacing. The 120 degree phasing system
> is very close to what results from using the crossfire phasing scheme
> recommended by W8JI and DX Engineering at that spacing. The
> crossfire system is broadband and can be used over several bands, and
> the current phases will vary accordingly.]
>
> The bottom line is that a single K9AY or EWE (which are essentially
> equivalent if properly installed) is a better receiving antenna than
> a single whip vertical, but using them in arrays may be much more
> complex than required for good low noise receiving performance. The
> only notable improvement for the arrays of EWEs or K9AYs is a
> reduction in the off-axis back lobes, which could be useful for
> attenuation of some low angle QRM. On the other hand, as K4SAV
> describes, the array of verticals has a null at zenith, which could
> help attenuate lightning static and NVIS QRM.
>
> It's also interesting that all of the 4 Square arrays are very
> similar in performance to a 1.5 wavelength Beverage or an echelon of
> 1 wavelength Beverages (staggered by 0.186 wl) with 135 degree
> phasing (although the back- and side-lobe structure is different.)
>
> Incidentally, models of the DX Engineering array actually show
> slightly better RDF (a few tenths of a dB) at closer spacings than
> 1/4 wl (with appropriate phasing). I suspect the arrays of EWEs and
> K9AYs would be similar.
>
> 73, Terry N6RY
>
>
>
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>
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