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Re: [TowerTalk] Coax Lengths for Stacked Yagis

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Coax Lengths for Stacked Yagis
From: Wes Stewart <wes_n7ws@triconet.org>
Date: Thu, 3 May 2018 15:34:20 -0700
List-post: <mailto:towertalk@contesting.com>
You don't say how they are to be switched but as a general case, I would make them all the same length.

Because of the different heights and depending on what the connection arrangement is, each Yagi will present a different Z to the respective lines. Hence each of those lines, even if the same length, will provide a phase shift different from the others. These differences may be insignificant but deserve analysis IMHO. Lines of different lengths compound any differences, especially when the frequency changes.

Wes  N7WS

On 5/3/2018 12:37 PM, Richard Smith wrote:
I am part of a team that is building a station that will incorporate stacked 
yagis on 20 thru 10 meters. We plan to put all of the RF switching at the base 
of the towers, for ease of troubleshooting and maintenance. My question deals 
with the lengths of the coax runs between the yagis and the switching box at 
the base of each tower.

Example - 15 meter stack:

Upper Yagi at 150'Middle Yagi at 120'Lower Yagi at 90'
One option is to run equal lengths of coax from each yagi down to the switch 
box, and coil up the excess coax from the middle and lower yagis. But does it 
make more sense to use shorter runs of coax from the lower antennas to the 
switchbox? Specifically, if the coax runs from the lower yagis are shorter by 
multiples of one-half wavelength compared to the upper yagi (using the velocity 
factor of the coax in the calculation), would all of the yagis still be in 
phase?
Thanks in advance,
73, Rich, N6KT

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