Wow. This belongs in a book and on a web page somewhere. Great post.
----- Original Message -----
From: "K9AY" <firstname.lastname@example.org>
Sent: Thursday, November 13, 2003 7:51 PM
Subject: [Antennaware] K9AY Loop modeling in NEC-2
> Pete and all,
> Here is what I have developed for K9AY Loop modeling... Remember,
> the antenna was "discovered" by modeling, all the hard data on
> terminating resistance and pattern shape were obtained through
> listening tests on the first unit. I have not found a model that
> need to be "tweaked" to match the observations.
> Method #1
> I model the loop exactly as it is constructed, connected to "Real"
> using the Sommerfield-Norton "High Accuracy" ground type. This is
> recommended procedure for NEC, because the currents in/out of ground
> unpredictable. However, using the segmentation on the list below and
> "Average" ground conductivity, I get modeled results that match the
> Because this model goes against NEC modeling guidlines, I rarely
> it. It suits my purposes, within strict limits based on LOTS of
> with this particular antenna type. I believe it is an acceptable
> just as with Beverages and EWEs when they are modeled with
> High Accuracy Ground.
> (Dimensions in feet)
> Wire 1 0,0,0 0,-15,4 #14 9 segments
> Wire 2 0,-15,4 0,0,25 #14 13 segments
> Wire 3 0,0,25 0,15,4 #14 13 segments
> Wire 4 0,15,4 0,0,0 #14 9 segments
> Ground -- "REAL" "HIGH ACCURACY" "AVERAGE" (.005, 13)
> Source: Wire 1, 0%
> Load: Wire 4, 100%, 400 ohms
> Freq: 1.83 MHz
> Method #2
> Instead of the two long wires used by W7EL, a model using "High
> ground can be created using (8) radials 30 to 50 feet, less than one
> above ground. Length doesn't matter too much, as long as the radials
> an area about twice the footprint of the antenna. Be sure the
> include two that are exactly in line with the loop.
> This model requires a terminating resistance much higher than what
> empirically determined, but it "follows the rules" and the pattern
> in the right ballpark. I never use this model -- it was developed
> "first cut" at making a model that met NEC usage guidelines. It is
> that this is an accurate model for a loop installed over radials,
> not how I make them.
> Method #3
> I have not yet thoroughly tested this modeling method, but it gives
> consistent results and appears to match real-world behavior.
> 1. Use the REAL/MININEC ground
> 2. Raise loop 1 foot above ground
> 3. Add a wire from ground to the junction of Wires 1 and 4 (which
> connected to Ground in the above wire list)
> 4. Feed/terminate the loop at the same points as above -- inner ends
> pulse) of the semi-horizontal bottom wires.
> 5. Add a 150 ohm resistive load in the new wire between ground and
> feed/term junction.
> MININEC ground models antenna impedance as if connected to perfect
> believe the resistor in the vertical wire represents the reduced
> in/out of lossy ground. 150 ohms is a "trial-and-error" value, and
> value probably varies with local ground conditions. In any case, the
> shape is right, dBi gain and feedpoint impedance are pretty close to
> High Accuracy Ground model I've been using.
> 73, Gary
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