Topband: receiving antennas

[Bill Tippett]

W8JI wrote:

>The person would could figure out how to use the pattern tables 
>that are exported by Eznec in a spreadsheet to determine S/N ratio 
>would be a top-band hero, because the data would express the 
>effectiveness of an antenna for receiving. We need directivity, not 
>gain.

        Actually I think this may already exist.  I do not have K6STI's
AO (Antenna Optimizer) program but I do have his Yagi Optimizer 7.0.
The following is from YO7 documentation:


       "---- F/B AND F/R -----------------------------------------------

	        YO uses a generalized notion of standard front-to-back
	power ratio to characterize pattern quality.  Conventional F/B
	is the ratio of forward power (at 0 degrees) to that radiated in
	the opposite direction (at 180 degrees).  YO's generalized F/B
	is the ratio of forward power to that radiated within a
	specified region to the rear of the antenna.  This is called
	front-to-rear ratio (F/R).  Yagi designs maximizing conventional
	F/B often have large backlobes at angles other than 180 degrees.
	Much better patterns result when you optimize a Yagi for F/R.
	The F/R region begins at 180 degrees and extends forward to a
	specified angle (90 degrees by default).  You can define the
	forward limit in 5-degree steps and as far forward as 5 degrees.
	This wide range lets you control sidelobes as well as backlobes.

	        During optimization YO uses RMS weighting to combine
	backlobe amplitudes within the F/R region.  The nonlinear
	weighting helps minimize peak backlobes.  But reported F/R
	figures use the peak backlobe in the F/R region, not the RMS
	value.  YO samples the radiation pattern in 5-degree steps for
	all F/R calculations.

	        For H-plane patterns of antennas over ground, the F/R
	region begins at the rear horizon and ends at the specified
	elevation angle.  This lets you minimize rear radiation over a
	range of elevation angles.

	        Use the Tradeoffs menu to change the F/R region.  Set it
	for 180 to 180 degrees (a single point) to obtain conventional
	F/B.  The F/R value depends on the extent of the F/R region and
	on the analysis plane selected."

My guess is that AO uses the same RMS weighting scheme which could be
applied to Beverages modeled with AO.  Maybe one of our reflector readers
(K9UWA?) that has AO can verify this.  BTW, K6STI is still in business
even though he does not advertise it.  See page 30 of July 2000 CQ for
an article about YO7...his E-mail is k6sti@n2.net...I highly recommend
YO7 having just used it to optimize my 10 meter KLM's. 

                                                 73,  Bill  W4ZV


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