Process and apparatus for transmission of binary messages by synchronized frequency shift keying

Abstract

Abstract A process for frequency modulation of binary messages in which the variables 0 and 1 are represented by signals of respective frequencies f0 and f1 differing by frequency Delta f. The process is characterized in that, to prevent undesirable phase modulation during the switching from one frequency to the other, frequency f1 is related to frequency f0 by deriving the signal of frequency f1 from a carrier wave form at the frequency f0 through modulation of such frequency f0 to obtain a single sideband by means of a signal of frequency Delta f which determines the rate of the switching intervals of the binary message. The apparatus comprises a first generator providing a carrier wave form of frequency fo, a first phase shifting circuit providing two first signals of frequency f0 shifted by 90*, a second generator providing a signal of frequency Delta f, a second phase shifting circuit providing two second signals phased 90* from each other, two modulators for amplitude modulating the two first signals by the two second signals respectively, an adding circuit for adding the outputs of said two modulators and having means for suppressing one of the sidebands and the carrier waveform so as to generate a signal of frequency f1, an electronic switching means operated at the frequency Delta f or a submultiple thereof for switching the signals of frequencies f0 and f1 in accordance with the message to be transmitted.

Inventors

• 👤 Jean-Marie De Rubinat

Bibliographic Details