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Joined: Dec 2007
Posts: 71
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OP
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Joined: Dec 2007
Posts: 71 |
It was pretty clever for the time.
Originally they needed 4 wires. One pair (usually 14 AWG) for the closed circuit telegraph loop (72 to 105 VDC) and the other pair for the telephone circuit.
Later on the design was changed to allow the telegraph and telephone circuit to use the same pair of wires.
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