Topband: Antenna Signal/Nosie

[Bill Hohnstein K0HA]

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A followup on my notes about my trying to come up with a better way
to compare the receive noise (eg static) reduction capabilities of
diverse receive antennas.  I felt a little embarrassed when listing
the relative noise figure for my 3 parallel Beverages planned for
this year since it wasn't much better than last year's 2 parallel
Beverages.  While I still planned revision to the design before
installation (crops not harvested here yet) I thought that I was
close to the final revision.  My reaction to this was, "Let's put
this new number to use and see if I can use it to improve my design."
While heavy on the numbers, I think that observing the progression
of changing one parameter (the phase of the wide spaced Beverage)
is useful in that it shows a variety of things happening with my
Beverage array:

      RELATIVE
PHASE  NOISE   AZ    dBi     BW     F/B    EL   ELBW   COMMENTS
  0    -8.08   40   -8.16   54.3   24.97   24   41.6   Prior listed #
 25    -8.21   46   -8.47   52.8   26.86   22   40.5   + minor #1 adj
 50    -8.35   49   -9.07   50.7   28.25   21   39.5
 75    -8.51   52   -9.99   48.2   29.60   20   38.2
100    -8.62   55  -11.26   45.5   28.70   18   36.0
125    -8.45   58  -13.03   43.1   26.06   17   34.7
150    -7.43   60  -15.29   44.9   22.21   16   32.9
 90    -8.60   53  -10.59   46.8   28.35   19   37.3   Chosen design

AZ = Center of azimuth lobe
dBi = dBi value of above lobe
BW = -3 dB bandwidth of azimuth lobe
F/B = Front of back of main lobe (NOT to "back" of Beverage)
EL = Center of elevation lobe at peak azimuth
ELBW = -3 dB bandwidth of elevation lobe

Note that while the Beverages all stay with a 40 degree azimuth
that the main lobe shifts clockwise with increasing phase delay
to Beverage #3 (the wide spaced one).  Being able to adjust the
phase of that Beverage (via a MFJ-1026) will be very useful!
Looks like I'll be shifting the Beverage wire azimuths to around
30 degrees to compensate.  Note that the 90 degree "Chosen Design"
numbers also include a minor change to the phase of Beverage #1.
Looking at the pattern as my receive noise figure improved, I
thought that becoming a "less clean" looking pattern would result
in a worse figure.  However, the decrease in the main lobe width
obviously made up for that.  Also apparent was there's a limit
to only observing main lobe width figure.

This changes my prior summary to:

            RELATIVE
  ANTENNA     NOISE   COMMENTS
Any omni ant   0 dB
2 ele vert    -3.14   Classic 90šspace/90šphase array for comparison
My xmit ant   -5.28
584' Bev      -6.31   Haven't helped me much over in-line w/xmit ant
881' Bev      -7.31
2 x 881' Bev  -7.86   6' spacing, stagger fed 1/4 wavelength
3 x 881' Bev  -8.08   Above, plus third spaced 0.4 wavelength (planned
                        for this season)
3 x 881' Bev  -8.60   Today's revision of the above

Note the minor changes to the Beverage lengths above correct my
"rounded numbers" previously listed.
While still subject to further revision, I think that his year's
European Beverage is now very close to its final design...

73,  Bill     K0HA



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