Please double check that EZNEC 3.0 does the averaging correctly. There are
two common errors:
1) calculating an arithmetic average of the dBi number, not of power.
2) calculating an average of an equal number of points at each elevation angle.
This substantially overweights the higher angles in
the average.
Either error will completely invalidate the result.
-- Eric K3NA
-----Original Message-----
From: topband-bounces@contesting.com
[mailto:topband-bounces@contesting.com]On Behalf Of Bill Tippett
Sent: 2003 November 11 Tuesday 22:52
To: topband@contesting.com
Subject: Topband: RDF
N4ZR wrote:
>I have been hunting for more information on RDF
It is available using EZNEC 3.0 which calculates
Average Gain over the entire 3D pattern. When choosing
3D Plot, "Average Gain" appears in the box at the bottom of
the summary screen as "Average Gain = -15.77 dB". You then
take max forward gain (from either Elevation or Azimuth plots)
and subtract Average Gain to get RDF. In this example, max
forward Gain was -1.81 dB, making RDF = -1.81 - (-15.77)
= 13.96 dB, so it's the ratio (or arithmetic difference in dB) of gain
in all directions versus gain in the desired direction. See here
for a summary:
http://www.w8ji.com/receiving.htm
RDF is better than nothing, but it essentially assumes
equal distribution of noise from all elevations and azimuths.
If you have an idea of the most likely azimuth and elevation
for noise (e.g. where thunderstorms typically are found from
your location), I feel you can get a better idea of array performance
by looking at the actual Az and El plots. Two arrays could have
identical RDF's, but be quite different depending on the source of
the noise. For example, one array might achieve its RDF by
compressing the forward beamwidth but another might have an
identical RDF by having very high F/R. If the noise was from
the backside, the latter would probably be the most effective.
73, Bill W4ZV
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