| 摘要 |
1,193,475. Digital transmission systems. WESTERN ELECTRIC CO. Inc. 26 July, 1967 [29 July, 19661, No. 34306/67. Heading H4P. Digital data is transmitted as a frequency modulated signal which comprises a waveform whose frequency varies smoothly from a base frequency # 0 to a higher frequency f+ or to a lower frequency #-, according to the bit-state, and back to # 0 in each bit interval. In such a signal the phase of the base frequency at the end of a bit period differs from that at the beginning of the period, and the direction of the phase change indicates the bit state. Transmitter.-Polar input bits, in which the voltage during each bit varies smoothly from zero to positive or negative and back to zero, pass to a tunnel diode oscillator whose output frequency varies correspondingly about # 0 . The amplitude of the input bits is such that the phase shift in the base frequency over each bit period is Œ90 degrees. Receiver.-The signal passes to a hybrid unit which delivers equal components, one via a 1-bit delay and 90 degree phase shifter, to a second hybrid which provides signals on its outputs depending on the instantaneous relative phase at the inputs, the signals being combined by resistors to provide the original data. Timing.-The received signal is passed to a frequency discriminator which feeds a full wave rectifier to provide a clock signal. |
