Topband: Interesting Loop Antenna Design and EZNEC

[Terry Conboy]

  On 2010-08-31 5:05 PM, rick darwicki wrote:
> Playing with a loop design and EZNEC I modeled a square loop 12' above the ground, 16' boom and 16' high. Corners at the top and bottom.
>
> First shot was a source at one end of the boom and an 800 ohm resistor at the other boom end corner. The result is a pattern with a very deep null off one end and an average gain of about -47 DB.
>
> Out of curisority I took out the resistor and put in a second source. By adjusting the phasing on the second source to about 13 degrees I can get the same or deeper null pattern with the average gain of about -16 DB.
>
> Does this mean the loop would RX 30 DB better and still have as good or better nulling?
>
> If you vary the size of the loop, you have to change the phasing degrees to get the null to peak. A loop 4 feet on a side shows the deep null at 6 degrees and average gain of -28 DB.
>
> These were all done over Real/mininec ground.
>
> Anyone tried this in the real world? As soon as I finish my bathroom remodel I might build on up and see.
>
> Any comments?
>
> Rick, N6PE
> ===========================================================================
Rick,

This works in theory, but the REALLY hard part would be getting the 
current phase and amplitude correct for the two sources.  When I modeled 
this, the drive impedances at the two source locations were nearly equal 
in magnitude, but one has a NEGATIVE resistive part.   And yes, removing 
that 800 ohm resistor will definitely make the gain go up!

It's usually a good idea to use the Real/High Accuracy ground in EZNEC 
since the coupled ground losses are closer to reality.  (For this 
antenna, it doesn't make much difference, however.) With the standard 
NEC2 version of EZNEC, the Mininec ground is usually only needed is for 
antennas that are physically connected to ground (but then you need to 
include resistive loads to simulate the estimated ground connection loss).

73, Terry N6RY