The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Jun. 07, 1977
Filed:
Dec. 05, 1975
Tadikonda Narashimha Rao, Morristown, NJ (US);
Rouben Toumani, Teheran, IR;
Bell Telephone Laboratories, Incorporated, Murray Hill, NJ (US);
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.