Topband: receiving antennas

[Bill Tippett]

W8JI:

>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.

W4ZV:

>        Actually I think this may already exist. 

        K6STI is indeed your hero Tom!  The following is from his AO
documentation and indicates a similar F/R optimization algorithm to YO7
which I posted previously.  I don't have AO and have never used it but
I'm sure Brian (k6sti@n2.net) can answer any questions.

---- PATTERN-QUALITY MEASURE -----------------------------------

	        AO uses a generalized notion of front-to-back power
	ratio (F/B) as a measure of pattern quality.  Conventional F/B
	is the ratio of forward power (at 0 degrees azimuth) to power
	radiated in the opposite direction (at 180 degrees).  AO's
	generalized F/B is the ratio of forward power to power radiated
	within a specified region to the rear of the antenna.  Antenna
	designs with good conventional F/B often have large backlobes at
	angles other than 180 degrees (for example, see BEVERAGE.ANT).
	Much better patterns result when designs are optimized for F/B
	over an angular region.  The F/B region begins at 180 degrees
	azimuth and extends forward to limits set by you.

	        The F/B region may be defined in the azimuth or
	elevation planes, or it may be defined over a solid-angle
	region.  The latter can be used to minimize rear power radiated
	at angles off the principal planes.  Use the Tradeoffs Menu to
	specify the limits of the F/B region.  You may specify the
	resolution at which the pattern is sampled.  Use fine resolution
	for complex patterns with many small lobes.  Use coarse
	resolution for smooth patterns to speed calculation.  The
	resolution value is the elevation-angle increment.  Azimuth-
	angle resolution automatically varies with elevation angle
	(fewer azimuth points are needed to cover the radiation sphere
	as elevation angle increases).

	        AO provides two methods for characterizing power within
	the F/B region.  The first method simply averages power over the
	region.  When F/B is optimized using this method, total power
	within the F/B region is minimized.  This is particularly useful
	with EME arrays to minimize total earth noise on receive.  The
	second method uses an L4 norm.  This mathematical technique is
	like that used to compute RMS power, but the fourth power and
	root are used instead of the second.  F/B computed using the L4
	norm is approximately the ratio of forward power to the power of
	the peak lobe within the F/B region.  When F/B is optimized
	using peak power, backlobe amplitudes are minimized while
	maintaining roughly equal amplitude.  This method is
	particularly useful with HF antennas since it minimizes worst-
	case interference from signals arriving at random rear angles.

                                                        73,  Bill  W4ZV


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