[RFI] SolarEdge Finds New Source of Solar System RFI

Jim Brown jim at audiosystemsgroup.com
Mon Jun 3 18:21:24 EDT 2019

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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