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Re: [RFI] SolarEdge Finds New Source of Solar System RFI

To: Rfi List <rfi@contesting.com>
Subject: Re: [RFI] SolarEdge Finds New Source of Solar System RFI
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Mon, 3 Jun 2019 15:21:24 -0700
List-post: <mailto:rfi@contesting.com>
That has ALWAYS been true -- EU Standards have nothing to do with it, other than educating (at least partially) on the subject. And there are elements of design that are not well known (or at least well-practiced) by the EMC community that have been well known in the pro audio world for nearly 25 years!  Consider "the Pin One Problem," exposed by the late Neil Muncy, ex-W3WJE in a 1994 AES paper. He also exposed a manufacturing issue with the shielded twisted pair cable that is still ubiquitous as "rack wire" in all sorts of studio systems that he dubbed "shield-current -induced noise" (SCIN). Thanks to the defect, shield current was converted to a differential voltage on the pair, so that, for example, mic wring running through the ceiling of a wood frame church would act as a an RX antenna for a nearby broadcast station and be detected either as a result of a Pin One Problem or excessive bandwidth in the audio chain. Mackie, a popular  mfr of otherwise good low cost gear believed that his audio chain should pass at least 2 MHz to minimize phase shift! These audio mixers and mix desks were unusable in downtown Chicago, where TV transmitters lit them up, and anywhere close to an AM station.

The very public stink I raised (and documented) forced the company to fix both issues.  This was late '90s - early '00s. The Pin One issue was also present in some very top-line microphones.

I published several AES papers on the RFI aspects of both the Pin One Problem and SCIN.

The power-line equivalent of a Pin One Problem is a green wire that fails to make contact with the shielding enclosure, and often for the same reason. It's present in many (most?) Astron power supplies, where the bonding point is insulated from the enclosure by paint.  This is a VERY common mechanism by which RF is coupled into a victim and out of a source.  There are applications notes on my website about Pin One and SCIN. k9yc.com I suspect Pin One as the mechanism by which backhaul signals at HF are coupled out of CATV internet systems.

In bar conversations in the late '90s, Muncy emphatically stated that Pin One Problems were the primary cause of RFI. A few years later, I did the research and published it in the form of several AES Papers that proved him correct. They're on my website -- scroll all the way down.

73, Jim K9YC

On 6/3/2019 2:35 PM, David Eckhardt wrote:
Jim, audio equipment meets its challenge with the immunity requirements that Europe places on it.   Analog circuitry is highly susceptible to external fields!  Design to withstand the EU standards is no simple task.  In addition, even the analog portions of the audio designs of today employ actives devices that, by themselves, could operate happily into the VHF and low UHF region (especially your low noise input stages).


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