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 > ____________________________________________________________________________________ Be a better pen pal. Text or chat with friends inside Yahoo! Mail. See how. http://overview.mail.yahoo.com/
