W8JI:
> If we want to compare two antennas, or optimize the length of an
> antenna, we need to compare the sum of noise response from all
> directions of noise arrival to the response in the direction (and at
> the angle) of the desired signal! Pretty much nothing else matters.
W4ZV wrote:
> Actually I think this may already exist. I do not have K6STI's AO
> (Antenna Optimizer) program but I do have his Yagi Optimizer 7.0...
As sent on this reflector about this time last year I came up with a
similar way for comparing my top band receive antennas. I was
trying to come up with a better way to help me design my 3 element
phased parallel Beverage array. I found it to be very helpful and
my receiving tests under real signal conditions closely matched the
numbers that resulted. Part of last year's message follows:
I came up with a number that does this [calculate the relative
noise immunity of receive antennas] 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.
RELATIVE OFF-LOBE NOISE
ANTENNA NOISE COMMENTS
Any omni ant 0.00 dB
2 ele vert -4.15 Classic 90ºspace/90ºphase array
My xmit ant -7.72 (3 in-line verticals--parasitic array)
584' Bev -9.74
2 x 584 Bev -12.25 My 1998/1999 268º Beverages
881' Bev -12.65
2 x 881' Bev -14.84
3 x 881' Bev -16.97 My early 1999/2000 Beverage Design
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)...
10/18 With my tests expected to be of low volume use for myself
I didn't incorporate it into a computer program--I did it manually.
It obviously would be better to have incorporated it into the antenna
design software (as per in K6STI's).
My Beverage fields are just now getting harvested of their corn.
Time for me to get serious about this year's Beverage design...
73, Bill K0HA
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