Transceivers for single channel carrier telephone systems
US4028628A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Dec 5, 1975 |
| Grant date | Jun 7, 1977 |
| Priority date | — |
| Expiry date | Dec 5, 1995 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH03G3/3057
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
Abstract
A single channel carrier system is disclosed in which carrier techniques are used to add a second private talking path on a normal telephone subscriber loop. A central office unit modulates the second subscriber's signal to an inaudible range while the remote subscriber's unit demodulates this signal to recover the voice signal. The same process is used in the opposite direction utilizing a different carrier frequency. Each unit includes a carrier receiver having automatic gain control circuits and a variable attenuation circuit. The automatic gain control circuit includes a direct current clamp to minimize excursions of the AGC signal in the absence of a received carrier. The variable attenuation circuit uses a diode bridge shunting the signal path and controlled by the AGC signal. A linear carrier oscillator is implemented by providing a constant current source of oscillation energy.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.