[Elecraft] K3S Microphone Cable

[Jim Brown]

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 <ve7pnq at telus.net>
> Date: 1/16/18 22:09 (GMT-06:00)
> To: jim at audiosystemsgroup.com, elecraft at mailman.qth.net
> 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: elecraft-bounces at mailman.qth.net 
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Jim Brown
> Sent: Tuesday, January 16, 2018 9:49 AM
> To: elecraft at mailman.qth.net
> 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.