[Amps] World's worst coax connectors

[vk6jx at bigpond.net.au]

Hi folks.

I've been following this thread with interest as I too have had experience
with sound reinforcement for rock bands.

But, my 42 year career was as an Electrical/Instrumentation Engineer with
major alumina refineries, iron ore mines, nickel refineries and then
engineering consulting here in Western Australia.

Every shielded single pair or multi pair instrumentation cable (read
low-level signals being conveyed through the noisiest HV/LV/variable speed
AC drives environment imaginable) all over the world, has the shield
grounded only at the receiving end - which is usually within the E/I
Equipment Room adjacent to the area control room. This is where these low
level signals are connected into the Honeywell or whatever SCADA system
which monitors and controls the plant. There is a "clean" instrumentation
earth system installed under each control room which is entirely independent
from the power earth installation to which all the motor cable earth wires
are bonded. The drain wires of the shields of all of these instrumentation
cables are grounded only to the clean earth system. The shields at other
ends of all of these cables - out in the field connected to thousands of all
types of transmitters - is not connected to anything.

This is the industrial standard everywhere.

Regards,

John VK6JX   

-----Original Message-----
From: Amps <amps-bounces at contesting.com> On Behalf Of Jim Brown
Sent: Monday, April 24, 2023 9:29 AM
To: amps at contesting.com
Subject: Re: [Amps] World's worst coax connectors

Interesting indeed -- I first proposed a concentric capacitance in the
course of an AES EMC WG meeting as a solution to the need to break the
shield at one end of a cable to prevent excitation of legacy Pin One
Problems. I was thinking "feed-thru" for the shield. Joanne Dow, a WG member
based around LAX, suggested the addition of the bead. This was in the late
'90s, and I knew nothing of ferrite then! It was John Woodgate, from the UK,
who proposed the circumferential array of SMT caps, and who subsequently ran
extensive tests of an engineering sample. Engineering people from Neutrik
had long been active in the WG.

Another critical piece of this series of Standards came from Bill Whitlock,
whose work on the Balanced Interface showed that if the cable shield is
interrupted, that the interruption must be on the receiving end. This was
counterintuitive to some of us, including me, but Bill changed our brand of
booze. In addition to being Chief Engineer of Jensen Transformers, the
world's best, and having done extensive design work at major LA recording
studios, Bill has had serious RF consulting projects in the UHF range. :)

The resulting product was a quite effective band-aid for VHF and UHF in
legacy equipment with Pin One Problems. Most (but not all) of the WG members
who made the most important contributions to AES EMC Standards were hams.

I was (and still am) Vice-Chair of the EMC WG, and chaired the writing group
that developed that series of Standards.

Also critical to our final product was understanding the difference between
shielding and grounding. We connect the shield to the shielding enclosure
NOT to "ground" it, but to make the shielding continuous! It was the late
Ray Rayburn (a ham) who came up with the phrase "shielding enclosure" to
solve some arguments with the "physics-challenged."

I learned a LOT from the serious brain-power during my work on AES
Standards. It was like free grad school!

73, Jim K9YC

  On 4/23/2023 4:07 PM, Paul Christensen wrote:
> The discussion in the link above concludes with a reference to the 
> Neutrik EMC series XLR connector.  It uses an integrated capacitor 
> between Pin 1 and the shell.  For anyone not yet bored by the 
> discussion, have a look at the bottom table, "Pin 1 Problem" in this 
> Neutrik application note where the EMC capacitors are shown:
> 
> https://www.neutrik.com/media/9117/download/typlical-application-emc-x
> lr.pdf
> ?v=1
> 
> I'm a bit skeptical of the effectiveness across a broad range of 
> EMI/RFI but it looks like it may be an "AES acceptable" way to join 
> two midpoint XLR connectors.  The top of the application points to my 
> original concern.  See "Interrupt of Circumferential Shield," and
"Connector Shell Floating."
> 

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