The only environmental issues that could affect audio are 1) magnetic
fields developed by faults in the power wiring in your home or leakage
flux from big power transformers; 2) a variable-speed motor controller
very nearby; 3) difference in potential between interconnected equipment
that creates leakage currents on cable shields.
Cable shields have NO effect on magnetic coupling at audio frequencies.
Twisting, however, is VERY resistant to magnetic coupling. #2 is by
magnetic coupling if the source is nearby. The cure for #3 is BONDING.
Magnetic coupling also occurs in loops that are part of the signal path,
like cable shields in unbalanced circuits. Coupling is proportional to
the area of the loop, so keeping bonding conductors as short as possible
helps. Also, by virtue of the difference in the resistance of cable
shields and bonding conductors, a beefy #10 or #12 bonding conductor
will carry far more of any induced current than cable shields that are
typically #18 - #22 gauge.
73, Jim K9YC
On 1/17/2018 4:35 AM, Clay Autery wrote:
Frankly... the electromagnetic environment in my home vicinity
prrsently is like trying to manage airspace in a war zone during a
major offensuve.
Sent from my Verizon, Samsung Galaxy smartphone
-------- Original message --------
From: Garry VE7PNQ <[email protected]>
Date: 1/16/18 22:09 (GMT-06:00)
To: [email protected], [email protected]
Subject: Re: [Elecraft] K3S Microphone Cable
Back in my broadcast years I worked at the low budget end of the
industry where we did what ever it took to get on the air at the
lowest cost possible. In small market stations where Radio Shack was
our primary local parts supplier we abused unbalanced lines to the
extreme as long as the cable length was not too long and the nearest
transmitter was not too close. Low cost mixers had 3 pin connectors
but with two pins grounded to accommodate a broad range of low cost
mics, cables and adaptors.
Later in life when I had more money, the cost of mixers, differential
amps etc was lower and the distance to high powered amateur radio
transmitters was inches rather than miles, I adopted a more rigid
adherence to broadcast standard low impedance cables even over
relatively short cable lengths of a few inches or feet. As good as the
noise rejection of new pre-amplifiers are, I still find separation of
shield grounding and the minus side of a mic input important with
modern radios. This has become more important in the era of huge
numbers RFI sources such as digital radios, local residential RFI from
IOT, LED lamps, cheap switching power supplies, thermostats and people
still using compact fluorescent lights.
OK honest truth, how many of us only have one radio operating at a
time? How often do you need your HF rig to reject RFI from your
VHF/UHF transmitter, computer accessories or switching power supplies
in our energy saving appliances.
I may be showing my age but physics doesn't change. Shielding external
noise before it reaches the input to the pre-amplifier is still an
effective strategy. I still use balanced lines when ever I can.
Garry
VE7PNQ
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Jim Brown
Sent: Tuesday, January 16, 2018 9:49 AM
To: [email protected]
Subject: Re: [Elecraft] K3S Microphone Cable
The nature of the shield matters a lot. Back in 1994, Neil Muncy,
ex-W3WJE (SK), published the landmark AES paper in which he exposed
both The Pin One Problem and Shield Current Induced Noise (SCIN). The
Pin One Problem is the (now) well known equipment design defect,
whereby the cable shield fails to contact the shielding enclosure,
first going to the circuit board, where shield current is coupled to
the circuitry. SCIN is a defect in the construction of "rack cable"
having a foil/drain shield, whereby the drain wire is twisted at the
same rate as the signal pair and is much closer (along the cable) to
one signal conductor than the other. This causes shield current to
induce a differential voltage on the signal pair.
Neil did his work on how these mechanisms coupled at audio
frequencies, but in multiple bar conversations when we met at
conventions, he said that both were also very strong causes of RFI,
and that Pin One was the dominant cause. In 2003, I did research that
confirmed this. Audio old-timers may recall that in the late '80s and
early '90s, Mackie mixers were almost certain to pick up AM broadcast
stations that were on the high end of the band. My work on
susceptibility of equipment showed that they suffered both from Pin
One Problems AND that the bandwidth of their audio circuitry extended
past 1 MHz! In attempting to use one of these mixers to test
condenser mics for RFI from FM and TV broadcast, I found that these
mixers themselves strongly detected RF from TV channel 2, and were
thus unusable!
I also tested the RF rejection of quad cables, including Canare, and
found that they were inferior in that regard to a good braid-shielded
cable like Belden 8412. Gotham Audio cable (an EU cable then imported
by the Neumann distributor) also performed quite well.
All of that work was published as AES papers. You can buy them for $10
each at aes.org, or you can download them without the AES logo from my
website for free. :) k9yc.com/publish.htm Scroll down to find the
AES papers.
As to the Heil cable -- I've never seen it, don't know its construction.
As Don notes, additional conductors can be useful for control functions.
73, Jim K9YC
On 1/16/2018 8:59 AM, Don Wilhelm wrote:
> The Heilwire is IMHO the best wire for ham applications because it
> contains additional conductors for PTT as well as a shielded twisted
> pair and is soft and flexible.
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