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:
Aug. 07, 1990
Filed:
Sep. 02, 1988
Joseph P McGeehan, Corsham, GB;
Andrew Bateman, Bath, GB;
National Research Development Corporation, London, GB;
Abstract
In transparent tone-in-band communication systems a notch in the frequency band is usually formed and then the resulting spectrum is translated in frequency to an intermediate frequency range as part of the transmission process. In a transmitter of the present invention a more simple arrangement is used in which the notch is formed directly in an intermediate frequency range by using mirror filters to divide an input signal into two portions and supply respective mixers, each having one output sideband in the intermediate frequency range. The mixers receive different reference frequencies and the mixer outputs are supplied to a summing circuit whose output is passed to a band pass filter to remove the unwanted sidebands. The original frequency spectrum is restored at the receiver by mixer processes of shifting the two selected sidebands similar to, but the inverse of, those used in the transmitter.