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Re: [RFI] Fan Noise on Repeater

To: rfi@contesting.com
Subject: Re: [RFI] Fan Noise on Repeater
From: rrath@charter.net
Date: Tue, 09 May 2006 15:52:03 -0700
List-post: <mailto:rfi@contesting.com>
The repeater housing (just the GR300 repeater) is bolted to a metal 
shelf, which inturn is bolted to the repeater cabinet (the entire 
repeater, duplexer, Bp filter, Bp cavity, etc.
I have two ferrite snap-together beads (very loose on the wires to 
the fan. Meaning 1/2" hole and the two wires for the fan going thru 
only once, not wrapped around several times. I do have a mic 
plugged into the Tx radio all the time. The fan came with the 
repeater (installed) when I bought it used. I am using only "double 
sheilded" coax inside the repeater cabinet.


Most common and forgotten is the noise is most often caused 
by the fan shaking something that is loose.

A loose connector, a loose connection, a pressure fit 
connection, a bad metal to metal contact on a cover, case, 
or cabinet, and so on. The fan could also be shaking an 
inductor and phase modulating the rig.

It very rarely is an actual RF noise generated by the fan. 
ESPECIALLY in a repeater.

The repeater, if constructed properly, should be VERY immune 
to RF sources from around the equipment. The RF input system 
in particular has to be very well shielded.

Although possible, it is actually unlikely to actually be RF 
radiation from the fan.

73 Tom 

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