Gregg, you are correct up to a point.
VHF/UHF yagis are usually several wavelengths in boom length as compared to
a 20M with say a ~40' boom.
With long booms you need comparably wider stacking spacing. You also have a
rather large set of side lobes to be concerned with and stacking height
becomes critical with some designs.
Or look at small VHF yagis such as a 3el 6M or a 5el 2M; stacking distance
for them is typically in the 1/2 to 5/8 wave region.
If you have access to the YO or similar program you can enter the data for a
particular design and watch the combined pattern as you adjust the stacking.
Sometime an eye opener.
----- Original Message -----
From: "Gregg Seidl" <firstname.lastname@example.org>
Sent: Friday, May 30, 2003 9:46 AM
Subject: [TowerTalk] antenna stacking
> Please forgive my ignorance of this but I come from a vhf/uhf background.I
> don't understand how you can stack 20 meter yagis at 30 feet and get
> 3 db gain that one would expect from stacking.That is not quite a half
> wave.I have a h frame set of 2m and 432 beams (4 antennas) and if I would
> put them at 1/2 wave I don't think you would get ANY gain.vhf beams are
> stacked at several wavelengths apart.What am I not getting.I know that as
> the element number drops the spacing can be closer but that seems to be
> to close.Even my new 6m beam which has 9 elements on a 50 foot boom has a
> stacking distance of 30 feet.Maybe the goal is not 3 db and more coverage
> arriving angles.The reason I ask is because I have a tribaner at 75 feet
> would like to maybe add a 2nd on at 40 feet someday?? Thanks Gregg K9KL
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
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