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Re: Cross boom length?



Hi All,
Rule of thumb is 1/2 Wave length of the lowest frequency antenna as a 
minimum, and more is better. When stacking two or more antennas for higher 
gain the spacing is related to the antenna gain, again 1/2 wave  is the 
minimum spacing.  All this goes away if the elements of the two antennas 
cross at 90 degrees and they can then share the same boom (ie the arrow 
antenna).
Also in a  related question,  the element spacing is measured center to 
center, this is important if elements are different diameters. Otherwise you 
can use front to front or back to back as well as center to center.
Measuring the elements from the  reflector reference of Zero, is done in a 
share ware program called "Yagi-Max". This program of DOS type, is a good 
program for understanding Yagi antenna behavor, including stacking and 
spacing. Once I got used to marking the boom starting with the reflector, I 
found making antennas is quicker with less mistakes. Bottom line is use the 
construction system you are most famillar with, and save the brain power for 
trying to understand the new things you are atempting to learn.
A few assumptions can cause several problems that do not converge on a 
common source, requiring a twisted thought process to straighten out all the 
problems with the twisted data.
Translation: Assumptions are VERY DANGEROUS!

Art, KC6UQH


----- Original Message ----- 
From: "Steve KA5YFC" <ssbrockw@swbell.net>
To: <amsat-bb@amsat.org>
Sent: Saturday, March 18, 2006 7:02 PM
Subject: RE: [amsat-bb] Cross boom length?


> Directive Systems has a pretty good AppNote on stacking antennas. It is
> aimed at getting antennas set up on VHF/UHF but I think that is would
> apply to satellite antennas also. It does explain the interactions of
> the antennas on each other and how you can compromise to get the most
> bands on the shortest mast.
>
> http://www.directivesystems.com/
>
> Look for the APP Notes on the left and then click on the link for how to
> plan multiple antennas on a single mast.
>
> I found it informative and it has given me several ideas as to spacing.
> I think that using circular polarized antennas, one would have the same
> stacking distance both in the H plane and the E plane.
>
> Just another item to look at.
>
> 73,
>
> Steve
> KA5YFC
> ----
> Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
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----
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