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[TowerTalk] Switching 450 ohm twinlead?

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Subject: [TowerTalk] Switching 450 ohm twinlead?
From: (L. B. Cebik)
Date: Fri, 6 Jun 1997 21:27:53 -0400 (EDT)

Unless you are using a matched 450-ohm load to 450-ohm lead, the impedance
bumps created by relay spacing will be in almost all instances meaningless
and minor, with no consequences for efficiency/loss of the power transfer.

One meaningful dimension of the design exercise is the fact that relays
tend to have pointy corner parts in the switching lines that may be quite
close to each other.  If the switching is at a high voltage point, arcing
is possible.  Hence, physical relay design is as important as the voltage
and current ratings, which should be high enough to handle either a high
voltage point or a high current point, since in a multiband antenna you
may encounter either/both.

Also, be sure that the relays can handle the high humidity that will
inevitably be present in the remote box.  Corrosion does not require
direct contact with rain drops.  Regular maintenance is a must on any
remote switching assembly, and periodic relay replacement should be
assumed as a fact of life, with thanks to lucky stars if it is not needed
in the Carolina atmosphere.  If you can hermetically seal the unit with an
inert gas filler, maintenance schedules can be longer.

Hope something here is useful.



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