| 摘要 |
1,205,279. Digital transmission systems. ENGLISH ELECTRIC CO. Ltd. 22 April, 1969 [23 April, 1968], No. 19162/68. Heading H4P. In a binary frequency shift transmitter, transients in the transmitted signal are minimized by changing the oscillator frequency at a fixed point of the waveform of the current frequency, e.g. at a positive-going zero amplitude transition. Mark and space bits at respective inputs 6, 7, together with the differentiated output of Schmitt trigger 9, control bi-stable 5 which switches oscillator 4 from one frequency to the other. The resulting frequency shift signal passes to line via a filter 8 and also to the trigger 9. The differentiated output of the trigger consists of a pulse at each zero-level transition in the transmitted signal, and prevents the binary data at 6, 7 from switching bi-stable 5 until the occurrence of such a pulse corresponding to the first positive-going transition in the current frequency to follow a change in bit state. |
