Very familiar with these , wonderfully well made and will outlast all of us
although in my part of the world they have fans Std .
To: Repeater-Builder@yahoogroups.com
From: [EMAIL PROTECTED]
Date: Sat, 24 Nov 2007 19:39:45 -0800
Subject: RE: [Repeater-Builder] 19" rack positioning question
I put a VHF repeater together this summer in a
Stromberg Carlson cabinet that the phone company
retired and had to install a fan in the top of the
cabinet to get the heat removed. The cabinet was
insulated with one inch foam on top, bottom, sides and
doors. It was a side-by-side rack cabnet with 19 inch
rack on one side and 26 inch rack on the other. By
adding some 2 inch spacers to extend the rack rails
forward, a GE Mastr II repeater fit on the 19 inch
side, and by removing the 26 inch rack rails, the
duplexer fit into the other side of the cabinet.
There were places for two exhaust blowers in the top
of the cabinet with a flapper to close off the blower
hole when it was not energized. The air entered the
cabinet directly under the 19 inch rack side, with an
RFI screen covering the hole and an air filter to
clean any debris out of the incoming air. The whole
thing sits up about 2 feet off the ground, so it is
real handy to get at the equipment. The 19 inch rack
side hinges out and access to the rear of the repeater
is excellent.
The GE power supply is on the bottom, with the
controller above it and the repeater at the top of the
rack. I originally mounted the 50 deg C (about 105 F)
thermal switch on the power amp heat sink, but found
the temp got too high in the cabinet before the fan
came on. By mounting the thermal switch to the top
plate of the power supply, I got the best temperature
control. I only used one exhaust blower as the
flapper keeps the other hole sealed.
On a warm sunny day at 7000 ft, the temp inside the
cabinet rose to an uncomfortable 120 degrees (80 deg
outside) until the fan was installed. With the fan
controlled by the thermal switch on top of the power
supply, the temp felt as cool inside the cabinet as
outside the cabinet. I should mention that this is an
outdoor cabinet and is sealed completely to keep any
water out. All entry points for wiring and coax are
on the bottom of the cabinet. Exhaust air is into a
pleneum at the top of the cabined with a screened
outlet across the front.
The GE power supply has vent holes in the bottom,
which wound up being directly above the 1 foot square
vent hole in the bottom of the cabinet, so as soon as
the fan comes on, outside air is brought directly into
and around the power supply. I plugged the entry hole
in the other side of the cabinet with a piece of
plywood, and the duplexer sits above it, so no outside
air necessary there.
It took a crane to get this cabinet installed on the
concrete footers we poured, as it weighs about 1500 #
with the equipment installed.
There are a number of pictures of this installation if
anyone is interested:
http://sbarcnm.org/CamelotInstallThumbnails.html
73 - Jim W5ZIT
--- Eric Lemmon <[EMAIL PROTECTED]> wrote:
> Barry,
>
> With all due respect, I think the appropriate
> response to your statement is:
> "Not necessarily."
>
> The typical Motorola Micor 100 watt repeater station
> will have the duplexer
> at the very bottom of the cabinet, with the power
> supply just above it.
> Then follows the unified chassis, and finally the
> 100 watt PA at the top.
>
> While your desire for cooling fans is well-intended,
> I daresay that the vast
> majority of 100 watt Micor stations- many of which
> remain in service today-
> are cooled solely by convection, and they seem to
> survive without fans.
>
> Let us keep in mind that fans do not "cool"
> anything; they simply move air
> around. If the ambient temperature in an uncooled
> transmitter shack is 120
> degrees Fahrenheit, the fan will simply raise the
> temperature inside the
> cabinet to 120 degrees F- which might be higher than
> the temperature inside
> the cabinet if no fans were used.
>
> 73, Eric Lemmon WB6FLY
>
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