[RFI] Chasing RFI

Jim Brown jim at audiosystemsgroup.com
Sun Oct 18 13:24:49 EDT 2015

On Sun,10/18/2015 8:51 AM, Charlie Gallo wrote:
> Any ideas how to proceed from here?

Some questions to help you think about it.

As you tune around a band, especially the lower bands, are there peaks 
of noise, with a center that sound like a growly tone? If yes, this 
noise is not power-system related, its an electronic source. And, of 
course, you could have both kinds of sources. Many of us do.

A great way to figure this out is to look with a spectrum display, 
especially one with a waterfall. Electronic sources will show bumps of 
noise, spaced 10-20 kHz across a band, and if they drift, they're 
switching power supplies. If they don't, they're running on some sort of 
clock, usually associated with a microprocessor. They will show up as 
straight vertical lines on a waterfall, wiggly if they're a switcher. 
Power line noise is impulse noise, and will show up as horizontal lines 
on the waterfall.

Listening with the 660, how far have you walked?  More than a block or 
two? Have you tried driving around listening between stations for the 
noise on an AM radio?

If you never heard it on the Aircraft band, you were probably not close 
enough to the source. In other words, it could be a lot farther away. 
The reason that an AM VHF RX is so useful is that the noise at these 
higher frequencies doesn't travel far on the power system wiring, but is 
radiated by wiring close to the source.

73, Jim K9YC

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