[Amps] World's worst coax connectors

[Jim Brown]

On 4/23/2023 11:02 PM, vk6jx at bigpond.net.au wrote:
> 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

Cable shields are not EARTHED, they are shields -- the late Neil Muncy 
correctly taught us that the earth is not a sump into which noise is 
poured. :)  And not all large scale performances are of rock music -- 
when I've recorded Tony Bennett live, and mixed audience sound for him 
outdoors a year or two later, it was a big band with strings, toys, and 
a harp. 32-48 channels carrying mics several hundred feet, with the sum 
of noise picked up on those cables (non-coherent noise increasing by 3 
dB for each doubling of the number of inputs, 6 dB if the noise is 
coherent), is very different from rock and roll, and even more different 
from instrumentation.

A study of Whitlock's 1994 AES Paper (reprinted in Jun 1995 Journal of 
The AES) is groundbreaking. JAES is in most engineering libraries and 
the Jun '95 issue got a special re-printing, because it included 
ground-breaking papers by both Whitlock and Muncy, as well as two other 
EMC papers from the same session. Many years ago, it could be ordered 
from the AES website for $10.

Whitlock's paper analyzed the balanced interface as a Wheatstone bridge, 
which led him (and us) to the recommended practice. For balanced to be 
achieved broadband, cable capacitance comes into the equation, and it 
was learned that the differing dyes used to color-code conductors caused 
their dielectric constant, and thus their capacitance to the shield, to 
vary, thus upsetting the balance with increasing frequency. That issue 
is solved by always terminating the shield at the sending end.

Remember -- the fundamental reason for breaking the shield at all is 
legacy equipment with a Pin One Problem.

  - 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.

In North America, all ground electrodes (earths) in a facility must, by 
Code, be bonded together. Isolated ground mains wiring is used for 
sensitive equipment, including sound systems; ground (protective earth) 
is bonded to earth and neutral at the point of entry to the premises, 
but isolated from all other contact with grounded objects. When power 
transformers are added for voltage transformation or noise isolation, 
neutral must be bonded to building ground at its secondary, and if that 
transformer fed isolated ground wiring, the grounding point would be at 
that transformer secondary.

73, Jim K9YC