[RFI] Noise to identify

[Jim Brown]

On 6/6/2021 1:48 PM, Charles Plunk wrote:
> Looking at on audacity and listening too I am guessing 60/120hz power 
> arc. But then again I have had so much of it in the past I hear it in my 
> sleep, lol.

The problem is that spectrum analysis of virtually any power handling 
electronics will also show strong power frequency components. The reason 
for using RF spectrum and waterfall as the first element of 
identification is to learn whether we're dealing with 1) impulse noise, 
the vast majority of which is the product of arcing in the power 
utility's distribution system, or 2) electronically generated noise, 
which is nearly always the harmonics of electronically generated 
square/rectangular waves that are either controlling power EXTERNAL to 
the power company's system, or 3) harmonics of microprocessor clocks.

A simple examination of the RF spectra, ideally including a waterfall, 
will immediately tell us which of these three types of noise we're 
dealing with, which is essential in knowing how (and in what frequency 
spectrum) to chase it.

Type 1 (impulse noise) extends across all frequencies, so is best chased 
at the highest frequencies where we hear it. When you get close enough 
to it, power line arcing can often be chased by visual or acoustic 
means. For a variety of reasons, type 2 varies widely with frequency, 
and must be chased on frequencies where we hear it. We can't chase it on 
the 100-500 MHz range where we can easily zero in on power line 
problems, because it rarely extends that high in frequency. It is common 
for both types to be quite strong, and to wipe out entire ham bands (and 
the AM broadcast band!).

Type 3 is usually the least problematic, because it's usually much less 
strong, and shows up as a steady carrier, or even one that turns on and 
off, or switches from one frequency to another.

Yes, experienced RFI chasers can often listen to a recording like the 
one from this thread and identify it as power line arcing. But the 
average ham lacks that aural experience tied to practical experience. So 
I classify this RF spectrum picture as an important early step in 
"knowing your enemy."

There's a lot more in my tutorial. k9yc.com

73, Jim K9YC