| 摘要 |
849,422. Code telegraphy. STANDARD TELEPHONES & CABLES Ltd. Sept. 18, 1958, No. 29854/58. Class 40(3). In a start-stop telegraph system of the type in which the characters are ciphered by being combined with a cipher text advanced character by character as transmission proceeds, the received message being deciphered by use of a similar cipher text advanced in step with that of the transmitter, means are provided for recognizing a false start signal having a duration sufficient to simulate a true start signal and for preventing the stepping of the receiving equipment in response thereto. The system comprises a regenerative repeater using a number of multivibrators and gated and ungated differentiating circuits. On reception of a true or false start signal on the line 51 a reset device RT is released which allows the apparatus to start. A pulse from device RT triggers an astable multivibrator B2 which gives its first pulse after 5 m.sec. and which controls distributers 56, 57. These distributers give pulses at times T5 tc T130 as indicated. Assuming a normal start period of 20 m.sec. and code elements of 20 m.sec. period, at 30 m.sec. after the beginning of the start signal there will be a code element on the line 55 and the store unit 58 will be opened by the pulse T30. This causes the store to be placed in a condition indicative of the code element on the line at T30. Similarly the remaining stores are opened at T50, T70, T90 or T110 to be conditioned by the code elements. After 130 m.sec., pulse T130 closes the reset device which stops the units B2 and thus 56 and 57. On reception of the next start signal the process is repeated but in addition the stores are opened by T25, T45, T65, T85 and T105 to send to the receiver line 52 pulses indicative of the code signal received in the previous cycle. Provision is made to allow the last character of a message to be read out and passed to the receiver without destroying the synchronism of the cypher codes at the transmitter and receiver. In the event of a short start signal, i.e. one lasting less than 5 m.sec., the first pulse from unit B2 will pass through gate unit GC3, which at this time is open as there is now no signal on the line, and triggers unit B3 which in turn causes the reset device RT to stop the working of the apparatus. If a stop signal is not received within 130 m.sec. after the start signal, the pulse T130 will pass through gate unit GC5 to trigger unit B7. This unit actuates an alarm 63 to indicate reception of an unsatisfactory signal. Specifications 843,563 and 849,423 are referred to.
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