RFI
[Top] [All Lists]

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

To: rfi@contesting.com
Subject: Re: [RFI] RFI every 15 KHz on 160 meters, suspect source is a manufacturing facility.
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Fri, 2 Feb 2018 21:06:47 -0800
List-post: <mailto:rfi@contesting.com>
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



_______________________________________________
RFI mailing list
RFI@contesting.com
http://lists.contesting.com/mailman/listinfo/rfi
<Prev in Thread] Current Thread [Next in Thread>