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Well I still don't understand the technicallity of balanced and unbalanced
on POTS. It is usually thought of as nominally 600 ohms balanced. 48 volts
DC fed +/- to two wires through two 500 ohm coils (chokes) and the AC
(audio) signal applied through two equal capacitors to those two lines at
the CO This was before we had opamps or even solid state but the principle
is the same today.
At the RX end so long as you do not reference anything to ground equal
currents flow. The AC signal at any given point on the line would be
balanced. If you connect any resistance or capacitance unequaly to either
side of the line you upset the balance and induce hum or noise.
When I was a kid we use to try to run our own phone lines, as dangerous as
it was. To save money we ran a single line, ground return. Needless to say
we ended up with nothing but 60 Hertz noise. We probably could have used
the free induced energy to power some circuits! If it had been two wire
line, even zip cord, it would have worked fine.
http://www.hut.fi/Misc/Electronics/circuits/teleinterface.html#general
Doug
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* Doug Crompton *
* Richboro, PA 18954 *
* 215-431-6307 *
* *
* doug@crompton.com *
* wa3dsp@wa3dsp.ampr.org *
* http://www.crompton.com *
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