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Re: [RFI] RFI every 15 KHz on 160 meters, suspect source is a manufactur

To: jim@audiosystemsgroup.com, rfi@contesting.com
Subject: Re: [RFI] RFI every 15 KHz on 160 meters, suspect source is a manufacturing facility.
From: Cortland Richmond <ka5s@earthlink.net>
Reply-to: Cortland Richmond <ka5s@earthlink.net>
Date: Sat, 3 Feb 2018 08:36:56 -0500 (GMT-05:00)
List-post: <mailto:rfi@contesting.com>
I've tried loops in a variety of configurations, shielded, unshielded, balanced 
and unbalanced, but when I could get close to the H field source, shielding and 
balance really weren't a problem.

I've also used semi-rigid plastic tubing [HV insulation] with a short exposed 
center conductor of coax inside  to probe for the E-field on PWB's and EUT's  
while investigating conducted emissions. In the photograph below, one trace 
shows the near-E-field high-frequency ringing of an on-board SMPS while the 
other trace shows trigger current from a LISN.


 One adapts to the requirement of the moment,eh?


-----Original Message-----
>From: Jim Brown <jim@audiosystemsgroup.com>
>Sent: Feb 3, 2018 12:06 AM
>To: rfi@contesting.com
>Subject: Re: [RFI] RFI every 15 KHz on 160 meters, suspect source is a 
>manufacturing facility.
>On 2/2/2018 1:00 PM, Cortland Richmond wrote:
>> quite small loop will do very well if one is in close proximity to the 
>> magnetic field of an emitter.  That is, there is a good deal of 
>> utility in entering the near field very closely. 
>Yes, indeed! Most electronic sources (and this is almost certainly and 
>electronic source) are current sources -- they radiate by simple antenna 
>action, AND also couple via their magnetic field. In the near field of a 
>current source, the magnetic field is strongly dominant.
>That said, there are other flies in the ointment. First, the shielding 
>(or lack thereof) of the receiver. If it's poor, internal wiring will be 
>the antenna (or the magnetic loop). Second, in systems that are 
>physically large, wiring carrying the noise current generates both an EM 
>and magnetic field. Variable speed motor controller are a common, and 
>very strong, noise source, and the noise Don is chasing is typical of 
>them. It's all too common for controllers and motors to be widely 
>separated, and the wiring between them radiates. And if that's not 
>enough, bypassing the noise to "ground" can create a loop for the higher 
>order harmonics that both radiates and establishes the magnetic field.
>Something like 15 years ago, Neil Muncy (the Pin One Problem guy) was 
>called in to troubleshoot massive audio frequency buzz from the power 
>system at the newly built New Jersey Performing Arts Center. The cause 
>turned out to be magnetic coupling of neutral current from controllers 
>for the motors that run the elevators, which coupled into microphone 
>wiring for the performance spaces. And the coupling mechanism within the 
>audio system was another important concept that Neil discovered, a 
>defect in how mic miniature, multipair mic cables are manufactured. He 
>called it "shield current induced noise," and the coupling mechanism is 
>magnetic. There's a detailed description of the mechanism on my website. 
>BTW -- it also couples well into the MHz range.
>73, Jim K9YC
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