[TowerTalk] Switching 450 ohm twinlead?

Bill Turner wrt@eskimo.com
Sun, 08 Jun 1997 11:55:15 GMT

On Sun, 8 Jun 1997 07:26:34 -0400 (EDT), "L. B. Cebik"
<cebik@utkux.utcc.utk.edu> wrote:

>> > Jim, some of the commercial relay boxes claim the include a heating element to reduce moisture build up.  When opened up the heater is a
>> 10 watt wire round resistor.
>> 73, Larry L.
>> wa0etc
>Heating elements that "drive out" moisture only work when powered.  This
>is dandy for commercial and military stations that are powered 24 hours a
>day.  For ham installations that may be on for only short periods each
>day, a special line may be needed to keep the heater going.  Maximum dew
>usually occurs during periods of maximum human sleep.  Hence, the need to
>resolve a conflict between the need for continuous power to the heater and
>the urge to depower everything when not present at the station--with
>attendant concerns about preventing this line from being an entry for
>surges on the station power line to the other equipment (and household
>electronics as well).  (No fair tapping the neighbor's power line for
>heater current.)  Although this line sounds trivial (10 watts to a heater
>that does not do any transmitting/receiving work), it deserves all the
>care of any other line going to the antennas.
Instead of a separate heater, you might consider just keeping the
relay energized all the time when not in use.  That's what I do for my
80/160 meter ground plane.  I made the box out of wood (thoroughly
waterproofed) so it would retain heat better than metal, with a
plexiglas front so I could see inside without disassembling.  It's
been outdoors in the Seattle rain forest for three years now and looks
and works great.  BTW, if you use plexiglas outdoors, orient it to the
north so sunshine won't degrade it.

73, Bill W7TI

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