Re: [IRCA] Are Broadside Nulls Deeper with Phased Active Loops?

[Nick Hall-Patch <nhp@xxxxxxxx>]

At 18:42 3/24/2009, you wrote:

>I am currently using a Wellbrook ALA-330S loop to cut the noise down to S-9
>by placing the broadside of the loop in the N-S direction.  Could I get a
>deeper broadside null (figure eight pattern) by phasing two or more active
>loops positioned with the planes of the two loops running North and South
>and separated by 1/2 wavelength?  Is there another configuration of two or
>more loops that could be phased by separation and one of the adjustable
>phasing devices such as the DX Engineering NCC-1 or the MFJ1025 that would
>give me a deep broadside null to the preferred direction of communications
>(East)?  (Of course, being able to communicate in more than an easterly
>direction would be nice but I can't see how to do that as I would need a
>steerable antenna system (electrically or physically) with very deep fixed
>direction broadside nulls.  )
>
>The write up on the Wellbrook phased array:
>http://www.wellbrook.uk.com/phasedarray.html shows a pattern similar to
>what I want to achieve with two loops at 180 degrees (1/2 wavelength
>separation, I believe they mean) and fed with zero phase setting.  But since
>they do not compare the results of the phased array with a single loop, I
>cannot tell if the broadside nulls are deeper with the phased array.

Awhile back I measured an ALA100 preamp using a somewhat smaller loop than what Wellbrook suggests, Roy...the null on a single loop was somewhat greater than 30dB, which agrees with theory, and may well be what you're getting already.   However, what Wellbrook shows with their phasing unit and 1/2 wavelength separation is a greater than 40dB null, and the pattern is less rounded than a single loop, so would be more directional east-west.  For example, they show a signal  would be down 6 dB at 45 degrees, while my single loop gave more like 3dB at 45 degrees.

With the phasing unit, you might be able to play the null a bit to attenuate your noise further, but no guarantees....especially as it seems you can't put a single null on it at present (i.e. it's not a point source).

best wishes,

Nick


*****************************
Nick Hall-Patch
Victoria, BC
Canada 

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