Re: NEC-LIST: Difference between F/B and F/R ratio?

On Nov 26, 2007, at 10:04 AM, Jim Lux wrote:

> Essentially it's the ratio between main lobe gain and the
> integrated side/back lobes. I don't know how 4nec2 calculates it,
> but one convention is to use "rear" as anything more than 90
> degrees from the main lobe.

Having never come across a definition for front-to-rear ratio, this
is pretty much what I did in cocoaNEC, but using the peak, rather
than the average of side and rear gains.

I took the peak response and then looked at the response of the
entire hemisphere behind the direction of the peak (not just 90
degrees in azimuth but the tilted hemisphere that depends on the
elevation angle of the main lobe -- i.e., everything behind the plane
that the main lobe is normal to). The maximum from that hemisphere
is then recorded and compared against the peak of the main lobe and
that gets reported as the "F/R ratio."

cocoaNEC's "F/B ratio" is computed by looking at all elevation angles
for the azimuth angle that is 180 degrees from the azimuth angle of
the peak of the main lobe, not just at the same elevation angle of
the main lobe.

cocoaNEC is a native Mac OS X Cocoa application that uses nec2c as
the compute engine. You can get an overview of what it does here

http://homepage.mac.com/chen/w7ay/Manuals/cocoaNEC/RefManual/
RefManual.html

In addition to a spreadsheet data entry for the model, it also has a
procedural program input, that is Turing complete enough that you can
write optimizing loops with. The procedural input looks like the C
programming language but is an interpreter and not a compiler, so it
does not have to go through a compiling phase.

Anyhow, the entire manual can be accessed from here

http://homepage.mac.com/chen/w7ay/Manuals/cocoaNEC/Manual/index.html

(Jerry, the acknowledgment to NEC-2 is at the bottom of this page:
http://homepage.mac.com/chen/w7ay/Manuals/cocoaNEC/Manual/
index.html , and also repeated the "About..." panel that is available
in many MacOS X applications.)

Very best regards

Kok Chen, W7AY
Portland, Oregon

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