[RFI] Powerline Bandwidth Characteristics

[Dan Zimmerman N3OX]

>
> Greg,
>

> I think "narrowband" sources that have lots of 60Hz and harmonics in them
> might be things like light dimmers and switching power supplies that operate
> at a higher carrier frequency.
>

OK, here's a picture of what happens on 160m when a 10kHz square wave source
is modulated with a 60Hz filtered square wave (Don't worry about the
filtering, I thought it was necessary, the picture is pretty much the same
without it.  I just rolled off the 60Hz signal above the 20th harmonic and
it doesn't really change the spectrum);

http://n3ox.net/files/switchermod.jpg

You'll see in this case that you get "centers" of strong signal spaced out a
few kHz and if you zoom in you get a forest of 60Hz and harmonic spacings.
So if you listen on any frequency in the 160m band, you'll tune into a
signal that has harmonics spaced every 60Hz.

If you listened on AM, you'd actually hear frequency-localized "power line"
sounding noise, because no matter where you tune in, the modulation is 60Hz
+ harmonics.

On SSB the frequencies would change.

73
Dan