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Re: [RFI] Guidance on finding noise?

To: rfi@contesting.com
Subject: Re: [RFI] Guidance on finding noise?
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Sun, 12 Jan 2020 10:53:50 -0800
List-post: <mailto:rfi@contesting.com>
On 1/12/2020 10:14 AM, Lee STRAHAN wrote:
  The point to all this is try looking at the noise with a SDR radio that 
should give you a wider bandwidth picture.

RIGHT! It is quite likely that the noise K2KW and crew are chasing is NOT generated by the power system, but rather some electronic or power control device in a home or business. Traditional methods used to "pin point a pole" make no sense for this kind of noise, which is why I keep on saying "LOOK AT THE SPECTRUM."

The traditional methods that ARE applicable are what Lee describes and loop antennas, in both cases connected to 1) an RX with a spectrum display (best) or 2) a portable RX using a loop antenna that tunes to the frequency(ies) where you hear the noise. For example, the broad coverage RX in my Kenwood TH-F6A talkie uses an internal loopstick below 10 MHz; the antenna input can be manually switched between that loop and the SMA connector. That's the upside; the downside is that it's not very sensitive, so you have to be either pretty close to the source or an external loop needs a preamp.

Another very important point -- virtually all noise generated by the power system is IMPULSE NOISE that is the result of arcing, and it looks like horizontal lines on a fast waterfall. Electronic noise, including that generated by power-handling and control equipment like motor controllers, industrial equipment, and switch=mode power supplies, looks like humps on a spectrum display and slightly "squiggley" trails of those humps on a waterfall.

A study of NK7Z's website is quite worthwhile. I also strongly STUDYING my own application note. k9yc.com/publish.htm

Bottom line -- audio frequency spectrum and o-scopes are the WRONG tools for anything but impulse noise, and a spectrum display is the RIGHT tool for electronic noise.

73, Jim K9YC

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