A quiz question for the OLD OLD OLD geezers amongst us

Thread Starter

KL7AJ72

Joined Apr 15, 2021
22
From a 1921 AT&T text.

You have two parallel two-wire LONG LONE phone circuits. How can you use these wires to carry an additional DC Telegragh signal with NO interference to the existing phone lines?

(P.S.: There were some REALLY smart cookies 100 years ago!)
 

nsaspook

Joined Aug 27, 2009
13,435

Ian0

Joined Aug 7, 2020
10,054
Are you referring to the "phantom pair"? Where the AC signals are transformer coupled into the two phone signal pairs, and the DC voltage is sent between the two pairs?
 

Thread Starter

KL7AJ72

Joined Apr 15, 2021
22
Are you referring to the "phantom pair"? Where the AC signals are transformer coupled into the two phone signal pairs, and the DC voltage is sent between the two pairs?
Yes...the phantom circuit. A few years later, they used the phantom circuit for another voice circuit, saving 50% of the wire used
 

nsaspook

Joined Aug 27, 2009
13,435
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