[RFI] Line Noise Spectragraph

Roger (K8RI) k8ri at rogerhalstead.com
Wed Nov 19 15:35:03 EST 2008

Paul Christensen wrote:
> 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 linked 
> 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 and 
> below that.  Span of the graph is 190 kHz.
> The frequencies of this noise pattern do not  change.  Tomorrow or a week 
> 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 where 
> the frequency and broadness changes.
You say the pattern will look the same. Are you referring to the 
overall, general shape or the individual pulses and spikes?
An electrical circuit arcing  or the RF from a nearby broadcast station 
can rectify where a couple of rusty wires come together and create a 
frequency based on the wire length as well as the station frequency, but 
I'd expect to see a strong peak with the strength tapering off either 
side of that.
> In AM mode, I hear what sounds very much like an SCR buzz with no apparent 
> sign of modulation.  It's always there (i.e., not something a neighbor is 
> turning on/off)  Does this look like an electric fence?  Plasma TV, fish 
> tank aerator?
It looks like an inverter, or possibly a battery charger to me. Any one 
in you community have solar power?  Some of the inverters used on those 
things are terrible and the number is growing fast.   An electric fence 
would normally be more like random noise, at least all of the ones with 
which I'm familiar.  Some of the older plasma TV were noisy, but the new 
ones are *supposed* to be quiet and it's unlikely a TV would be on 24 
hours a day and I never saw one that could be heard very far. OTOH some 
inverters can be heard for several city blocks or more.

When you add in a malfunctioning piece of equipment the possibilities 
get kind of large.
> It is not coming from my home.  I pulled the main 200A breaker and fed my 
> 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 tired 
> of feeling guilty when the neighbors want to know why I'm running all over 
> the place in our gated community.
Just tell them the truth. If they can't handle that I certainly wouldn't 
feel guilty.

73 and good luck,

Roger (K8RI)
> Any help as to the pattern would be greatly appreciated and I mean greatly.
> Paul, W9AC
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