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:
May. 17, 1977
Filed:
May. 14, 1976
Peter Bragas, Hildesheim, DT;
Uwe Matzold, Salzgitter, DT;
Blaupunkt-Werke GmbH, Hildesheim, DT;
Abstract
A frequency recognition circuit includes a first phase locked loop to detect the carrier tone frequency, which locks to the detected frequency and provides the frequency-modulation frequency to a second PLL for modulation frequency recognition. When the predetermined carrier and modulation frequencies are recognized, an AND-gate provides a signal that removes a short-circuit from a capacitor that then begins to charge through a time constant circuit. The time constant circuit triggers a threshold switch after a period determined as the minimum duration for a signal and the threshold switch operates to advance a flipflop which performs a switching function and, at the same time, changes the time constant circuit so that the threshold switch will operate the next time on a signal of a different minimum duration. The decoder is designed to switch the output of a radio receiver on and off for selectively listening to traffic announcements.