On Sun, 29 Jan 2006, Glenn Little WB4UIV wrote:
> Why would you mount the second antenna upside down???
Assumably the owner of the tower wants as few non-earning antennas on the
tower as possible. And the ham owning the repeater doesn't want to buy
another piece of feedline.
> Is this to keep the coax to the two antennas close together and gain the
> loss through the coax to the upside down antenna??
Just to keep the feedpoints closer together and minimize additional losses
after the diplexer up the tower. Phase relationships and all.
> Is it to ensure early failure of the upside down antenna because of
> moisture buildup??
If the antenna is built correctly and/or designed for inverted mounting,
it will have a removable drainplug in the top end of it and a matching
threaded hole in the bottom which the drainplug can install into.
> Is it to cause the signal to go toward space rather than back to the ground
> due to any possible down tilt built into the antenna??
Was downtilt mentioned? Obviously, if the antenna has downtilt, it's not
the appropriate choice for inverted mounting.
> I would use folded dipole antennas due to their grounded nature. The
> colinear antenna tend to have problems with flexing and lightning. When
> all but the bottom quarter wave section is disconnected due to flexing
> or lightning, there is no way to determine that you have an antenna
> problem from the ground.
I'm fond of the folded dipole as well, but there are support kits for the
fiberglass sticks. There is no such thing as a free lunch however since
the harnesses on the folded dipole may also present several potential
failure modes.
--
Kris Kirby, KE4AHR <[EMAIL PROTECTED]>
"BIG BROTHER IS WATCHING YOU!"
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