1977-05-02
1978-07-25
Claffy, Kathleen H.
179170R, H04B 158
Patent
active
041031180
ABSTRACT:
This autobalance hybrid circuit is used to connect a 2-wire duplex telephone line to a 4-wire line which has separate receive and transmit pairs. The impedance of a balancing network automatically is adjusted to equal the impedance of the 2-wire line, thereby maximizing echo return loss. "Howling" and "singing" are eliminated, regardless of changes in the 2-wire line impedance. Balancing is achieved by comparing the absolute values of the receive line audio voltage components appearing across two coupling transformers, one associated with the 2-wire line and the other with the balancing network. A control signal, indicative of the difference between these components, alters the balancing network impedance until equal voltages are achieved. In this condition, the receive signal cancels out as a common mode in the output circuit, so that none of the receive line audio is returned to the transmit pair.
REFERENCES:
patent: 2282464 (1942-05-01), Edwards et al.
patent: 2302374 (1942-11-01), Mitchell
patent: 2531883 (1950-11-01), Kaelin
patent: 3178521 (1965-04-01), Brown
patent: 3582563 (1971-06-01), Cragg
patent: 3875350 (1975-04-01), Fischer
Claffy Kathleen H.
Myers Randall P.
Synanon Foundation, Inc.
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