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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