Automatic gain and return loss compensating line circuit
US4132863A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Dec 20, 1977 |
| Grant date | Jan 2, 1979 |
| Priority date | — |
| Expiry date | Dec 20, 1997 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04M1/76
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
Abstract
The disclosed T-type line compensation circuit reduces the gain and return loss variations when customer equipment is connected to a central office or PBX over telephone lines of various lengths. A linear resistor of a first series leg is thermally coupled, as a heat source, to a positive temperature coefficient (PTC) resistor of a second series leg. The shunt leg consists of a series connection of a bilateral zener diode, linear resistor, and varistor. The resistance value of both the second series leg and the shunt leg of the line circuit vary automatically with the direct current in the line to minimize gain variation due to telephone line length variation. The thermal feedback to the PTC resistor varies automatically with the direct current in the line to minimize return loss variations seen by the customer equipment. PAC FIELD OF THE INVENTION This invention relates to a line circuit for compensating telephone loop line and return loss variations due to variations in line lengths. PAC BACKGROUND OF THE INVENTION In the telephone loop plant it is frequently necessary to transmit and receive signals over telephone lines of various lengths. These telephone loop length variations …
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.