[RFI] New Interference at kk0sd

Jim Brown jim at audiosystemsgroup.com
Sun Mar 21 19:29:13 EDT 2021


On 3/21/2021 1:28 PM, Charles Plunk wrote:
> Its sounds like 120hz to me (power lines ). I recorded a segment and run 
> it through Audacity, expanded it out, and can see the spikes at about 
> that rate.

Sound of the noise in an RX can be deceptive. Some electronic noise 
sources SOUND like impulse noise but they are not. The excellent DF 
advice from several very smart guys is exactly right IF it is impulse 
noise, but because most electronically generated noise comes from power 
handling or control equipment (switch mode power supplies in equipment 
and battery chargers, variable speed motor controllers), it will also 
have very strong components at power frequencies. And all power control 
noise will show the same 60, 120, and their harmonics, just like impulse 
noise.

These power control devices use square and rectangular waves in the 
range of 10-20 kHz to do their thing, and they produce strong harmonics 
all the way up to 10M and beyond. Unlike impulse noise sources, they 
don't usually get up to 2M or 440 MHz where we can chase them with our 
directional antennas tuned to those frequencies -- instead, we must 
chase them where we can hear them. In addition, most of us have MANY 
noise sources, so it's easy to get on a wild goose chase if you don't 
know which kind of noise you're chasing.

THAT'S why I keep urging folks to study the waterfall FIRST.

73, Jim K9YC


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