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Re: [RFI] Noise to identify

To: rfi@contesting.com
Subject: Re: [RFI] Noise to identify
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Sun, 6 Jun 2021 23:21:56 -0700
List-post: <mailto:rfi@contesting.com>
On 6/6/2021 1:48 PM, Charles Plunk wrote:
Looking at on audacity and listening too I am guessing 60/120hz power arc. But then again I have had so much of it in the past I hear it in my sleep, lol.

The problem is that spectrum analysis of virtually any power handling electronics will also show strong power frequency components. The reason for using RF spectrum and waterfall as the first element of identification is to learn whether we're dealing with 1) impulse noise, the vast majority of which is the product of arcing in the power utility's distribution system, or 2) electronically generated noise, which is nearly always the harmonics of electronically generated square/rectangular waves that are either controlling power EXTERNAL to the power company's system, or 3) harmonics of microprocessor clocks.

A simple examination of the RF spectra, ideally including a waterfall, will immediately tell us which of these three types of noise we're dealing with, which is essential in knowing how (and in what frequency spectrum) to chase it.

Type 1 (impulse noise) extends across all frequencies, so is best chased at the highest frequencies where we hear it. When you get close enough to it, power line arcing can often be chased by visual or acoustic means. For a variety of reasons, type 2 varies widely with frequency, and must be chased on frequencies where we hear it. We can't chase it on the 100-500 MHz range where we can easily zero in on power line problems, because it rarely extends that high in frequency. It is common for both types to be quite strong, and to wipe out entire ham bands (and the AM broadcast band!).

Type 3 is usually the least problematic, because it's usually much less strong, and shows up as a steady carrier, or even one that turns on and off, or switches from one frequency to another.

Yes, experienced RFI chasers can often listen to a recording like the one from this thread and identify it as power line arcing. But the average ham lacks that aural experience tied to practical experience. So I classify this RF spectrum picture as an important early step in "knowing your enemy."

There's a lot more in my tutorial. k9yc.com

73, Jim K9YC


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