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Re: [RFI] IMPROPER AND PROPER SHIELD TERMINATION TECHNIQUES

To: rfi@contesting.com
Subject: Re: [RFI] IMPROPER AND PROPER SHIELD TERMINATION TECHNIQUES
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Sun, 24 Nov 2019 16:21:33 -0800
List-post: <mailto:rfi@contesting.com>
Excellent, Dave. This is a perfect example of "The Pin One Problem and how to avoid it. The AES Standards Committee published AES48 to address this issue about 15 years ago, which was first raised by the late Neil Muncy, ex-W3WJE in an AES paper in 1994. Pro audio interconnections are carried on shielded twisted pair, and for reasons of system architecture, equipment is often widely separated. To avoid issues with legacy equipment that was built with the problems you have noted, and what Neil called "the Pin One problem" because Pin 1 of XLR connectors is the cable shield, it is necessary in that equipment to leave the cable shield open at audio frequencies so that triplen harmonics of mains power can't flow on cable shields between widely separated equipment. Neil's paper was published in the June 1995 edition of the Journal of Audio Engineering Society. He and I were subsequently elected Fellows of the AES.

Almost 20 years ago, I proposed, and our WG developed, the concept of an XL-series connector where pin 1 was terminated to the shell via a circumferential ring of chip capacitors, and with a suitable ferrite bead around the through contact to Pin 1. Neutrik, a dominant mfr based in EU of XL-connectors for pro audio put our concept into production. This solved a widespread problem of VHF/UHF RF from broadcast stations being detected on equipment designed with the Pin One problem.

It is quite likely that noise in the 3-5 MHz region radiated by both CATV and DSL systems carrying upstream data is by this mechanism.

73, Jim K9YC

On 11/24/2019 12:56 PM, David Eckhardt wrote:
Dave Cole, our 'leader' has been kind enough to post this to a www page.
Here is the link - THANK YOU, DAVE!!

https://www.nk7z.net/wp-content/uploads/2019/11/IMPROPER-AND-PROPER-SHIELD-TERMINATION-TECHNIQUES-23-NOV-2019.pdf


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