Topband: B7P

[Jim Brown]

On 4/3/2024 8:13 AM, W3HKK at roadrunner.com wrote:
> This thread implies that Life in China comes with huge QRM-powerline
> noise, which makes a lot of sense.

Since the introduction of switch-mode power supplies, the fact that they 
are cheaper than traditional linear supplies, and the mandate for their 
use about 20 years ago, they, and other electronic noise sources like 
power control electronics for motors and solar systems, have become the 
the dominant noise in most of the world. While power line noise is still 
there, it is a total mistake to assume that noise we hear comes from 
arcing in defective equipment and hardware on power lines.

I commend this applications note I prepared about eight years ago on the 
topic. It begins by showing how we can determine whether it's the 
impulse noise generated by arcing (mostly) on power lines, and the 
electronic noise. Their RF spectrums are very different, and there are 
differences in the ways we need to chase them.

http://k9yc.com/KillingReceiveNoise.pdf

and this slide deck for a talk at Visalia in 2017.

http://k9yc.com/KillingRXNoiseVisalia.pdf

NK7Z has developed excellent techniques using a very inexpensive (under 
$150, last I looked) SDR RX to identify multiple electronic sources and 
reveal the times of day they are active. Topbander WD8DSB has done 
excellent work on methods of chasing to the source(s). NK7Z's work can 
help us avoid chasing our tails when multiple sources are present (and 
they often are), and can tell us what times of day to chase them.

Bottom line -- it's still critical to use DFing to get to the source, 
but electronic noise sources have both drastically increased noise 
levels around the world, and made finding the source more complicated.

73, Jim K9YC