[RFI] A Switcher it was!!

[Pat Thurman]

I have recently been plagued with a very similar problem and just 
discovered the source!  Here's the story...

Several weeks ago I started noticing a peculiar almost time related 
broadband interference largely confined to 40m.  It sounded very much 
like white noise and was S9 in strength.  Everywhere.  From below 5 mhz 
to over 9 mhz.  Not sure but that the range is maybe just a reflection 
of the bandpass filter characteristics of my radio.  After seeing Dan's 
post I started listening more carefully to the noise and sure enough I 
noticed a number of 'growlers' just like he posted.

In the course of hunting the noise, I had noticed that it seemed to come 
on at what seemed to be almost a predetermined time.  Eventually, I  
found that my son's clock radio was going off at about the same time.   
A couple of times, I was able to get the noise to go away simply by 
unplugging the clock radio so I began to think this was the source.  
About this time, W6WRT posted that it sounded like a switching power 
supply.  Armed with that, I continued looking.  I noticed that I could 
get the pitch of the 'growlers' to change slightly when I would turn one 
particular ceiling fan on and off.

To make a long story short, it turned out to be my wife's computer power 
supply.  It seems almost like the particular circuit in the house was 
acting somewhat like a tuned circuit.  A disturbance anywhere on the 
circuit could trigger some sort of instability in the power supply and 
make it start spewing this noise.

Since it's time to upgrade her computer anyway, I won't bother with just 
swapping out the supply so she'll be happy!  And I won't be plagued with 
any more noise for a while.

Life is good!!
--
73, Pat K7KR




Dan Kovatch wrote:

>I have noticed a strange  'group' of signals mainly centered on the 40 meter
>band. The signal sounds a bit like power line noise but may actually be at a
>higher frequency-kind of a 'growl' more than a raspy 120 hz . The 'noise'
>seems to peak every 140KHZ and is detectable from below 6 mhz to about 8
>mhz-this range may be greater but I haven't tuned more spectrum yet  It does
>appear to fade quickly as the freq increases from 8Mhz on. The strongest
>peaks are about 20 over s9 in the 40 meter band (which may be due to a
>resonant antenna,etc) The noise is relatively narrow band at about 5 KHZ max
>before beginning to fade out. Using 500hz filters in the AM position the 40
>meter peaks seem to be at (6880), 7020. 7160, 7300. The frequency of these
>peaks varies over time by about 5 khz. This interference disappears once in
>a awhile but I have found no apparent patterns
>
>I have killed every circuit in the house and am pretty sure it does not come
>from inside the QTH (it's always possible I overlooked something) . The next
>step is to put the 706 in the truck with the 40 meter ant and 'cruise' the
>neighborhood.
>
>Any wisdom or ideas will be greatly appreciated.
>
>Merry Xmas and Happy New Year!
>
>W8CAR
>Dan Kovatch
>zone 4 and 8/ohio/EN81oj
>www.geocities.com/w8car
>www.geocities.com/w8car/classics
>
>
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