In general, as the stacking distance exceeds optimum, the mail lobe
beamwidth continues to deacrease. The gain does not increase as one might
expect
because the grating lobe amplitude increases and "eats" the extra apparent gain
associated with the narrower main lobe.
At 144Hz and higher frequency, the added grating lobe amplitude can hurt
receive s/n if the lobe sees a noisy power source such as man made noise or sky
noise from our galactic center.
At 50MHz and lower, the background noise is so high that it makes little
difference if the grating lobes see these noise sources.
There are complete chapters and books to read all about this and a good
starting point is one of the VHF/UHF manuals if you can find one (all the ARRL
manuals are out of print).
73,
Gerald K5GW
In a message dated 1/2/2009 3:31:44 P.M. Central Standard Time,
k9kl@centurytel.net writes:
What happens to an antennas pattern when you stack it at more then "best"
spacing? I have been thinking about going to a 3 stack instead of a 2 stack
of 6M-7JHV's. M2 says 25 feet is best but 30 feet fits my tower better. What
happens to the stacks pattern. I know when understacked the gain suffers. I
would stack them at 32,62 and 92 feet. They would be controlled by an Array
Solutions stack match box. I already have the 2 stack going and really like
it but I think I miss some of the DX because I'm a little to low. I also
want to try some 6 meter moonrise and moonset EME. I can't wait for channel
2 to be gone when they go all digital. Channel 2 just kills me to the SW.
Any thoughts or ideas would be great! Gregg K9KL
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