GB1429265A - Modulator-demodulator - Google Patents

Abstract

1429265 Data transmission; FSK systems INTERNATIONAL STANDARD ELECTRIC CORP 10 April 1973 [11 April 1972] 17128/73 Headings H4P and H4L A F.S.K. transceiver has a combined modulator-demodulator comprising a fully integrated common circuit to perform conversion of binary coded to frequency modulated signals reversely, which circuit comprises an oscillator, a frequency divider with reset device, a code to determine the ratio of the frequencies transmitted or received, and a comparator connected to the divider and encoder. The transmitting part of a F.S.K. transceiver comprises oscillator 1, frequency divider 2, comparator 3, encoder 4, signal transmitter, e.g. teleprinter 5 and a flip-flop 6 interconnected as shown and controlled by a switch CA. The frequency divider ratio is determined by decoder 4. When the nth condition of divider 2 is identical to the output condition of encoder 4, comparator 3 delivers a pulse which resets divider 2 to one of a pair of ratios, selected by switch 8 the output from which passes through filter 7 to line. In a receiving condition zero crossings of incoming signals are detected at 31 and encoder 4 sends to comparator 3 a code corresponding to the central frequency. When coincidence occurs, comparator 3 delivers a pulse to flipflop 28 turning it on and at the following reset the condition is transferred to flip-flop 29 which stores the information until the next cycle; flip-flop 28 is reset via delay circuit 30. If the signal/noise ratio is low compensation is made by applying the output to a shift register set at the rate of zero crossings and on which a two out of three majority decision is made. The arrangement is stated to provide signals without phase discontinuity provided that binary signals occur at the end of each division cycle which may be achieved by flip-flop 6.