[RFI] Sinusoidal type noise on 6 meters (wx3k at yahoo.com)

[Jim Brown]

On 11/4/2023 8:06 PM, Chris L. Parker wrote:
> Dave is exactly correct. I apologize; I misspoke.
> 
> We locate the noise first and then determine the source.

I strongly disagree. For as long as I've been a ham (67 years), "power 
line noise" has been the knee-jerk assumption. For at least 20 years, 
that has been an increasingly bad assumption. Last I heard, all 
generated by power lines and power disto equipment is some form of 
impulse noise, which starts out life as extemely wideband, with radiated 
strength vs frequency strongly dependent on the antenna that transmits 
it. This stuff exists, of course, and it may have gotten worse with 
failures to provide sufficient maintenance over the years.

The most important characteristic of impulse noise is that the highest 
frequencies decay at the greatest rate with distance from the site, and 
the exact frequency where we listen doesn't matter, only the part of the 
frequency spectrum. Another important characteristic is that it's 
radiated by the power company's lines

BUT -- the dominant form of noise that most of us hear is ELECTRONICALLY 
GENERATED noise. Switch-mode power supplies have been mandated for 
energy conservation for at least 20 years; anything sold after around 
2000-05 that plugs into the wall has one of these beasts either built-in 
or as a wall wart/line lump. Power control electronics of all sorts is 
another common type -- variable-speed motor drives, voltage regulators, 
DC-DC and DC-AC converters, battery charge regulators, are notorious 
sources. These electronic sources generate RF spectrum (often unique to 
the device type or method of power control). The vast majority run on 
random frequency time base, and produce impulses at harmonic frequencies 
related to the clock frequency, amplitude modulated by noise. They show 
up in spectrum as humps of noise at their harmonics, typically 15-30 
kHz). A typical home includes several dozen electronic noise sources.

The most important characteristics of electronic noise are that 1) it 
repeats periodically with frequency, and that the period is related to 
the clock generating it. With electronic noise, it matters greatly were 
you listen. 2) It is primarily radiated by wires connected to the 
source, the vast majority of which are in the homes and businesses that 
are Customers of the power system.

So the very best first to do is figure out which type of noise we're 
looking for. As fundamental as "know thine enemy!" With these sources, 
we must be listening on THEIR frequency(ies). And, because the relative 
directivity and strength of any source is strongly related to the 
antenna that radiates it, the efficiency of the radiator can vary 
strongly with frequency and direction.

FWIW, I have never recommended comparing "noise signatures" as a first 
step.

So YES, we do go looking following the same principles developed by our 
great-grandfathers, but in today's world, that generic type of source 
(electronic or impulse) may cause to use very different tools.

73, Jim K9YC