I said:
>The "Wullenwever" antenna was never a low-noise high performance antenna.
It was simply a system designed to find direction over a very wide
frequency
range. The multitude of elements increased bandwidth, but the physical
width
in wavelengths is the primary determinant of directivity.
Lee said:
While I will agree that the Wullenweber antenna was never designed to
be a
low noise antenna, I fail to see why it is not. My copy of TM32-.......
manual
on the US version shows some pretty good directivity specs. On the low
band
starting at 2 MHZ the beamwidth was 11 degrees with the side lobes down a
minimum of 18dB. The maximum elevation was 30 degrees. Also the range
specified was 4000 nautical miles. And its outer element diameter was
1116 feet.
The sharpness comes from the wide area.
The 48 low band elements were 35 feet tall with a 120 foot tall
reflecting screen.
The 48 elements primarily give it bandwidth. With an 1100-foot array width,
the 160 meter element spacing only needs to be about 300-400 feet. That's
only three to four elements necessary, with three to four more (spaced
35-130 feet back) to make it unidirectional.
160-80 meters would double the number of elements.
It is the broadside area that gives us a narrow pattern, and the number of
elements in that area that gives us the bandwidth. We can't let spacing get
too wide between broadside elements. There is a chart here:
http://www.w8ji.com/stacking_broadside_collinear.htm
The more elements we use, the wider the allowable spacing in wavelengths.
Our limitation, at least for low-band use, is our available space and the
phase differences in signals a few wavelengths apart along the ground.
Watching phase difference between elements spaced 2-wavelengths apart is
interesting. I've found it quite possible to have an array too large for 160
meter skywave because of constantly changing phase differences at wide
spacings.
I'm sure a 1200-foot wide array would not be nearly as useful as the pattern
might lead us to believe. I have to break things spaced that wide into cells
that I run in stereo.
73 Tom
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Topband Reflector
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