|Subject:||[Antennaware] K9AY Loop modeling in NEC-2|
|From:||Pete Smith <email@example.com>|
|Date:||Thu, 13 Nov 2003 17:20:53 -0500|
I have been working with NEC-2 modeling arrays of K9AY receiving loops,
with the thought that if end-fire or broadside arrays of these things could
be made to work well, it would be a neat alternative to the Beverages I
don't have room for.|
In the process, I've run into the basic issue of how to model the K9AY loop. On his web site, at <www.w8ji.com/k9ayloop_mod.EZ>, Tom has posted a modeling file for this antenna which he attributes to Roy Lewallen, W7EL. It appears to be an effort to work around the NEC-2 problem with wires connected to ground, by connecting the two ends of the K9AY loop instead to counterpoise wires that run perpendicular to the plane of the loop for 100 feet in each direction, 6 inches off the ground.
The trouble is that if I run this file in NEC-2, I do not get anything like the cardioid pattern K9AY reports, with a steep null to the rear. At best there is a slight concavity in the 3D pattern at the mirror image to the maximum forward signal, but the F/B is no more than about 11 dB, and the RDF is about 8 (not too bad, by the way).
If I model the antenna with the loops connected to ground, while still using the Sommerfeld-Norton ground, I get results that are much like K9AY's, but MultiNEC warns me that the results cannot be trusted. If I use the recommended alternative technique of substituting MiniNEC ground and adding loads to simulate the ground connection resistance, the pattern reverts to one that looks very much like that resulting from Lewallen's counterpoise approach.
I'd appreciate advice on:
1. the validity of the various approaches.
2. what would be an appropriate load resistance to use for ground conductivity in the miniNEC ground case.
3. In the miniNEC ground approach, if both the source and the load on that leg of the antenna are specified as being located at the same place, I believe they will appear in parallel. For better accuracy, should I place the source one segment further "up" the leg from ground, so that the load will be in series betweren the source and the ground?
73, Pete N4ZR
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