Loop-around test circuit for telecommunications lines

Details Loop-around test circuit for telecommunications lines Loop-around test circuit for telecommunications lines

1977-04-18

1978-04-25

Olms, Douglas W.

H04B 346

Patent

active

040864480

ABSTRACT:
A control unit circuit for loop-around testing of telecommunication lines improves over its predecessor by circuitry that accepts a tone from either of the incoming lines without directly connecting the lines, thus to prevent fraudulent use of telephone lines that was possible in the past. The key circuit is an amplitude comparison circuit that detects a tone only within a certain frequency range. The circuit locks on to the detected tone and produces a corresponding sinusoidal output signal having the same level as the incoming tone.

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patent: 3389234 (1968-06-01), Cotner
patent: 3674947 (1942-07-01), Chulak
patent: 3704348 (1972-11-01), McIntosh et al.
patent: 3742155 (1973-06-01), Buck et al.
patent: 3790723 (1974-02-01), Stewart
patent: 4021625 (1977-05-01), Bradley

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