Topband: receiving antennas

[Bill Hohnstein]

W8JI said:

>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.

Knowing the limitations of my number, I tried to come up with
something better.  Consider the following noise situations:
  #1  Point source of line noise
  #2  Line noise/electric fence noise coming from a distance away
           from radiated lines that results in 45º arrival azimuth
  #3  Static generally coming from a 180º azimuth.
  #4  Static coming pretty much equally from all directions.
How does one number represent the best receive antenna for all
four (and more) situations?  A sharp deep null would solve the
problem for #1 but wouldn't help #3 or #4 at all.  And, I'd want to
go at solving #3 differently from #4.  The best that I can say is
that an educated use of K6STI's or my number can help in the
design of a receive antenna.  Example:
Assuming situation #3 above and the dreamed of case where the
desired reception is 180º away from the center of the static.
Assuming a typical Beverage having a relatively narrow main lobe,
other than the fact that it probably also increases the antenna's gain,
making the main lobe more narrow won't significantly reduce noise
pickup.  Therefore, just include the 180º opposite of the main lobe
(+/- 90º from the "back-lobe") in the root-sum-square radiations
being calculated to compare to the main lobe's level.  More gain
will help the number, less wide (180º) back-lobe suppression will
increase the number, but decreasing reception 45º off of the main
number won't change it at all (because it's assumed that the
reception limiting noise isn't coming from that direction).  Different
particulars would change how that number was calculated so that
it represented the noise in that situation.
I'm either missing something, or there's not one number (handled in
one way) that everyone can use for all noise reduction situations.

73,  Bill     K0HA


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