[RFI] Line Noise Spectragraph

Morse, Earl (E.A.) emorse at ford.com
Thu Nov 20 17:15:40 EST 2008

It looks like harmonics from a Switch Mode Power Supply (SMPS)and since
almost all electronics use SMPS technology it could be anything from a
TV to a computer to a battery charger.  Good job on eliminating your QTH
as the culprit and you are on the right path for finding it in the
neighborhood.  Not sure how close your homes are in your neighborhood
but smart money says to start with the houses closest to your antennas
and work farther out.  A receiver with a loopstick antenna should give
good directionality and be able to isolate a QTH as a potential source
before you ask everyone in the neighborhood to pull their breakers.

Earl N8SS


Message: 1
Date: Wed, 19 Nov 2008 14:53:52 -0500
From: "Paul Christensen" <w9ac at arrl.net>
Subject: [RFI] Line Noise Spectragraph
To: <rfi at contesting.com>
Message-ID: <005401c94a80$8cbb8a60$063ca8c0 at Dorm>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";

Once again, I am at my wits-end.  Just when I got the utility company to

clean up a four-year noise issue, I now have this.  Please see the
spectrograph below.

Beginning down around the BCB, I have the following noise pattern every
~ 56 
kHz.  The linked photo is centered on 3601 kHz but it extends well above
below that.  Span of the graph is 190 kHz.

The frequencies of this noise pattern do not  change.  Tomorrow or a
from now, the pattern will look the same and the frequencies will be the

same -- so I would rule out a random power company arc of some sort
the frequency and broadness changes.

In AM mode, I hear what sounds very much like an SCR buzz with no
sign of modulation.  It's always there (i.e., not something a neighbor
turning on/off)  Does this look like an electric fence?  Plasma TV, fish

tank aerator?

It is not coming from my home.  I pulled the main 200A breaker and fed
transceiver by battery power.  All home alarm battery systems were 
completely shut down and removed from their power source.

I will soon use a small SWBC receiver to try and hunt for this but after

four years of dealing with the other noise issue, I'm getting sick and
of feeling guilty when the neighbors want to know why I'm running all
the place in our gated community.

Any help as to the pattern would be greatly appreciated and I mean

Paul, W9AC


More information about the RFI mailing list