[TowerTalk] stacking distances

Fri Jan 2 16:51:22 EST 2009

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 at 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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