[Premium-Rx] Fan Noise

[Tisha Hayes]

You can try to run the fan when it is removed from the transmitter. Some
designs are just "screamers", usually this is due to the blade design but I
have run across some with very noisy bearings. A good example of a loud fan
is what is installed in the Harris RF-350K power supply deck. Many of those
suffer from bearing problems.

If you can find the right fan frame size you may run across a fan that will
give you the same CFM and pressure rating as what you are using now. When in
doubt, go higher.

In my console I use eight additional 120 VAC fans to keep the air
circulating for the tube based equipment. This is in addition to the fans on
the RF-350K's and the Harris 500 watt amplifier. I recently ran across some
48 volt fans that put out a much higher CFM, even when running them off of
24 VDC. As I climb through the console I am replacing the AC fans with the
DC fans one at a time. I even stuck a fan onto the RF-590 just to blow air
through the chassis.

I have a "break glass in case of emergency" type thermostat in the console
so if the internal temperature rises above 120 F the fans that are running
at 24 volts will cut over to full power, 48 volt operation. On the power
control panel I have a latching relay tied to a switch and an LED to alert
me that the temperature was exceeded at some point when I was not around. I
never power down the console and some of the radios are operating in an
unattended mode or across a remote Ethernet link (ROIP (radio over IP) and a
digital control channel).

I added a duct that pulls air out of the crawl space and goes into a turbine
fan that came off of a high voltage switchgear cabinet (VERY NOISY and draws
about 5 amps at 120 VAC, good thing it is mounted under the house). Since it
is usually in the 50's and 60's down there (even in an Alabama summer) I can
blow air up into the console for rapid cooling.
-- 
Ms. Tisha Hayes/ AA4HA
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"I'll be a diode, cathode, electrode
Overload, generator, oscillator
Make a circuit with me." -- The Polecats