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From: whit@milton.u.washington.edu (John Whitmore)
Newsgroups: sci.electronics
Subject: Re: Problem with aquarium heater producing radio interference
Keywords: aqua heater hig freq radio interf
Message-ID: <12253@milton.u.washington.edu>
Date: 4 Dec 90 01:32:15 GMT
References: <1990Dec3.222022.6991@unixg.ubc.ca>
Organization: University of Washington, Seattle
Lines: 19

In article <1990Dec3.222022.6991@unixg.ubc.ca> twong@civil.ubc.ca (Thomas Wong) writes:
>
>Hello. I'm having problems with my aquarium heater and I was wondering 
>if anyone might be able to help. During the heater on/off transition stage,
>the heater not only makes static noises which I can hear, but it also
>creates some high frequency interference that disrupts the reception of
>my AM radios. 

	Either switch bounce or the Neon pilot light can cause RF output
from an aquarium heater.  A simple ceramic capacitor across the AC power
line, located as near the switch/pilot light as possible, should cut the
noise.  Try for 0.01 uF, 500 WVDC; Radio Shack has this as 272-131,
for 500 millibucks, or 272-160 for a little higher breakdown voltage.
	A more elaborate scheme would be to use the mechanical switch
to trigger a triac (solid state AC switch) so heater startup would
make only a single 'tick' rather than multiple bounces.  The last time
I looked at aquarium heaters, they seemed to have room for such things.

	John Whitmore


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