[amsat-bb] Stacking (helix) antennas

["Ib Christoffersen" <oz1my@xxxxxxxxx>]

Hi all, 
Some years ago I run an article about stacking antennas in the 
AMSAT-OZ Journal. 
The easy way to calculate the stacking distance 
I got from G3RUH. 
As others have said the idea is to just 
let the effective areas toutch each other. 

This can be written as: 

D = (squareroot (Gi)) / pi 

Gi is the antenna gain in real numbers NOT dB. 

D is in wavelength. 

A 16 turn helix will have a gain of approximately 
15 dB - that is 31.62 times - result D = 1.8 lambda. 

The ARRL Antenna Book, 1991 page 11 - 15 gives the 
same result. 

Simulations with EZNEC verified the results. If you 
use the result from the equation - and have access to 
a simulation program you can fine tune the stacking 
distance with regard to the level of side lobes compared
to the gain. 

73 de OZ1MY/Ib 


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