Topband: Antenna Signal/Nosie

[Bill Hohnstein K0HA]

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I'm probably near overkill, but my last note's numbers appeared to be
little more than directivity figures (with the Beverage results 
perhaps corrected for the antenna's inefficiency) changed to negative
numbers.  I'm back to thinking that my original idea is the best:

> Perhaps it would be something like comparing the root-sum-square
> values that do NOT include the main lobe along with the gain
> numbers(?).

I came up with a number that does this by comparing the root-sum-
square radiation that's 35 or more degrees off of the main lobe
center with the peak radiation on that main lobe.  Since the antenna
can't discriminate against noise arriving from near the same azimuth
as the desired signal, including noise from that direction destroys
showing much of the directional antenna's benefit.  And since the
off-lobe noise figures are compared against a signal coming from the
main lobe, the benefits of antenna's gain/directivity are also shown
in the the new number.  Comparing the new numbers with past figures:

             RELATIVE  OFF LOBE
  ANTENNA      NOISE     NOISE    COMMENTS

Any omni ant    0 dB      0 dB
2 ele vert     -3.14     -4.15    Classic 90ºspace/90ºphase array
My xmit ant    -5.28     -7.72
584' Bev       -6.31     -9.74
2 x 584 Bev             -12.25    Last year's 268º Beverage
881' Bev       -7.31    -12.65
2 x 881' Bev   -7.86    -14.84
3 x 881' Bev   -8.60    -16.97    Revision

Who's in favor of a 17 dB improvement in signal-to-noise ratio?
If there's much noise arriving on the main lobe, the real improvement
will be less.  If the limiting noise is arriving 70 degrees or more
off of the better receive antenna's lobe center, improvement can
be greater than the listed figures.
I now can start to better understand why static coming from a storm
500 - 1000+ miles away on the main lobe of my 2 x 881' Beverage last
year was often the limiting factor for my reception (coupled with 
the low elevation angle that my Beverages have)...
I came up with a new design for a high angle reception antenna (at
least for me) that I'll be trying this season as well.  I should be
back on topband before long.

73,  Bill     K0HA




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