Coded telegram communications circuit - uses combined encoder and decoder with HF crystal oscillator

摘要

A combined message encoder and decoder has a crystal oscillator and, on the sending side, a message input circuit, a pulse divider a counter, three decoders for giving out short pulses at the 8th, 18th, and 28th count. If any of these pulses can reach through to point 'A', a reset pulse for the counter as well a stepping pulse for the message sequencing unit is produced. Its outputs are normally at logic high but when active go low. When a binary 'O' is to be sent this is to be represented by a signal interrupted at the 8th pulse. If the next digit is to represent a binary '1' the 8th pulse interruption must be suppressed by disabling the AND gate, i.e., when one output goes low. A message start or message finish stop signal is generated by another output. The reception portion of the unit produces a reversal of the process. Its outputs derive from a counter decoder with high tolerance for clock frequency deviation at the distant sending station.PS.