[Boatanchors] 2nd Newbie Q

[D C _Mac_ Macdonald]

I believe that your recommendation (in two-pair cables) of using Black for the Common and White for the "Hot" runs counter to normal AC mains practice for "polarity" and is likely to cause confusion and MAY result in negative safety aspects. Otherwise, I understand your points. 
 
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* 73 - Mac, K2GKK/5 * 
* (Since 30 Nov 53) * 
* k2gkk hotmail com * 
* Oklahoma City, OK * 
* USAF & FAA (Ret.) * 
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> From: brianclarke01 at optusnet.com.au
> To: duvallddennis at gmail.com; w2hx at w2hx.com
> Date: Thu, 11 Sep 2014 21:20:05 +1000
> CC: boatanchors at mailman.qth.net
> Subject: Re: [Boatanchors] 2nd Newbie Q
> 
> For really good quality interconnects at audio frequency, you should run 
> balanced lines, ie, two-core shielded cable. In this way the shield performs 
> only one function - shielding. The two internal cables then carry the 
> differential that is your audio signal. If you try to get the outer shield 
> to perform two functions, ie, shielding and carrying one part of the 
> differential signal, then any mains transformer, motor or electrical noise 
> generator within cooee will induce AC Voltages in the outer shield. This 
> Voltage on the shield will be seen at the 'receiving end' as signal; we will 
> hear it amplified as hum and noise.
> 
> Coaxial cable for carrying audio signal is OK for very short lengths inside 
> a chassis, or inside one metal cabinet where there are no enclosed mains 
> transformers. How to use twin-core shielded? At the sensitive (receiving) 
> end, connect the shield and one of the internal pair (eg, black) to the 
> ground and the other of the internal pair (eg, white) to the input 'hot' 
> terminal. At the other (sending) end, connect the black wire to ground and 
> the white wire to the signal output. Leave the shield unconnected.
> 
> If after all this, you still have hum and noise, you may need to lift the 
> mains ground lead above the chassis with say a 100 Ohm resistor. This will 
> give you safety and it will significantly attenuate any ground-loop induced 
> Voltage. The next step after this, is to use truly floating differential 
> circuitry, such as transformers. This is the kind of thin,king applied in 
> high quality audio recording studios,
> 
> At RF, different rules apply. Here, you should ground the shield at both 
> ends and at somewhere between every one-twentieth and one-fiftieth of a 
> wavelength along the coaxial cable. In this case, you are making the coaxial 
> cable part of the ground plane.
> 
> 73 de Brian, VK2GCE.