[Elecraft] P3 visualizing local noise

[Jim Brown]

On 3/30/2011 11:10 PM, Fred Atchley wrote:
> My P3 started displaying persistent clumps of noise across each band. These
> clumps reoccurred at about every 72KH over most bands.

This is the signature of a switching power supply. They are everywhere, 
and most of them are noise RF noise generators. Spectrum displays like 
the P3 are very useful in exposing noise sources like these.  You find 
and eliminate one and you start seeing weaker ones. The noise comes and 
goes and you and your neighbors turn on and off the equipment powered by 
these nasty little buggers.  You'll also see them drift up or down in 
frequency as they warm up, and drift up and down as their oscillator 
frequency is dithered (frequency-modulated by noise).   RFI regulations 
limit the field strength at a single frequency. Dithering is a cheat 
that makes it easier to stay below those limits by spreading the noise 
over the dithered bandwidth.

I recently identified the source of really loud noise on 12M as coming 
from the switching power supply for my SteppIR controller.

73, Jim K9YC