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[TowerTalk] "Antenna Mast Design" in NCJ by W7NI

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Subject: [TowerTalk] "Antenna Mast Design" in NCJ by W7NI
From: (Kurt Andress)
Date: Thu May 15 02:18:22 2003
>    Stan's article was the first to address mast forces. But according to 
>Dick Weber, K5IU, PE, Stan's article has some errors in it. Unfortunately he 
>didn't elaborate on them or provide the proper equations. 
>    The better and more accurate mast forces info is in Dave Leeson's, W6NL, 
>ex-W6QHS, book "Practical Design of Yagi Antennas" which I think is out of 
>Steve     K7LXC

>From: Dino Darling <>
>You can buy this book at HRO (,
>as well as other places I'm sure!
The W6NL(ex-W6QHS) book does not contain the current methodology either, 
it was published prior to Dick Weber's paper. But, it is still a great 
source for all kinds if valuable information, like wind load formulas 
for zone wind speeds from different specifications. The URL below 
contains a page about that also, which should help everyone think twice 
before they cite a wind speed relating to something.

The "crosswind principle", presented by Dick Weber (K5IU), for 
determining loads developed on antennas by the wind is explained in the 
ARRL Antenna Handbook, 19th Edition (circa Y2k), Chapter 22 "Antenna 
Supports". Along with, how to determine mast stress, and a new allowable 
antenna area limit for a freestanding tower when the load (or loads, 
antenna, mast, rotator) is not placed in just one location right at the 
top of the tower like the guy who designed the tower expected.
20 sqft at the top of the tower is different from 20 sqft in several 
places on a mast above the tower top. This chapter also contains a 
diagram and explanation of a technique for "tramming' an antenna up into 
place on a tower, and another technique for cleverly snaking it up past 
guys. All useful stuff for those contemplating getting antennas off the 

As discussed many times in the past on this reflector, all of these 
things require antenna "projected areas" to be used with the wind load 
formulas, not the so called "effective areas" that are reduced by some 
amount (usually 2/3 of projected). BE SURE TO ASK your antenna 
manufacturer what his area figure means, unless he has already explained 
it in his literature. You need the right area for evaluating everything 
that holds the antenna up there.

Kurt, K7NV

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