[RFI] IMPROPER AND PROPER SHIELD TERMINATION TECHNIQUES
jim at audiosystemsgroup.com
Sun Nov 24 19:21:33 EST 2019
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!!
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