Topband: Power Line Noise Direction Finding

[Tom W8JI]

Good work and thinking, Don. Sometimes noise is tough to locate.

> techniques work).  Here is a link to a simple website I created that
> contains pictures, oscilloscope screen shots of receiver audio, and links
> to video recordings that I made.
>
> http://sites.google.com/site/powerlinenoise/

Listening though narrow filters tends to make all noises look increasingly 
the same, eventually with enough selectivity they all become sinewaves. This 
is why waveforms on receiver audio outputs, especially with narrow filters, 
has limited value. Using your logical deduction, a 120 Hz audio output is 
typical of a single phase arc.

120Hz audio tone noise can also be a full wave line rectified, poorly 
filtered switching supply. But in that case the noise is frequency periodic 
as the dial is turned.


> 1) I tried using a portable 160 meter AM radio with portable shielded DF
> loop, but I was unable to zero in on the suspect pole (with 100 percent
> certainty) using this equipment, and it was not until I used the VHF AM
> radio with lots of attenuation that I was able to identify the suspect 
> pole.

That is pretty much how it always works. Low frequencies get it to the 
general line, and increasing frequencies get it narrowed to an area.

I use this unit, although a wide selectivity AM portable all band receiver 
would do almost as well:

http://www.w8ji.com/power_line_noise.htm


Locating noise is an application where more bandwidth is usually much 
better.

73 Tom