Circuit for generating a narrow band signal for digital data transmission over telephone lines

Claim 1

IN APPARATUS FOR THE SELECTIVE ALTERNATIVE TRANSMISSION OF DIGITAL INFORMATION BY MEANS OF TWO FREQUENCYSHIFT SIGNAL FREQUENCIES OF A CARRIER FREQUENCY WITHIN CONSECUTIVE EQUAL SIGNAL-PULSE PERIODS, THE COMBINATION COMPRISING A TRANSMITTER OUTPUT ELEMENT, AT LEAST TWO CONTINUOUSLY OPERATING SINE-WAVE GENERATORS WHOSE SINE-WAVE OUTPUTS ARE HARMONICALLY RELATED AND MUTUALLY PHASEDLOCKED, AND SIGNAL-GENERATING MEANS OPERATIVE TO SELECTIVELY ADMIT ONE OR THE OTHER OF SAID SINE-WAVE OUTPUTS TO SAID OUTPUT ELEMENT ACCORDING TO THE DIGIT TO BE TRANSMITTED AND TO EFFECT EACH CHANGE-OVER AT A POINT AT WHICH THE GRADIENTS AND MOMENTARY VALUES OF THE RESPECTIVE SINE-WAVE OUTPUTS ARE SUBSTANTIALLY EQUAL, WHEREIN ONE OF THE TWO PHASE-LOCKED SINE-WAVE GENERATORS OPERATES AT ONE HALF AND THE OTHER AT ONE QUARTER OF THE PULSE-PERIOD FREQUENCY, MEANS BEING PROVIDED FOR SUPPRESSING THE EMISSION OF A FURTHER PULSE AT THE END OF THE FIRST PULSE