| 摘要 |
998,083. Speech immunity circuits. STANDARD TELEPHONES & CABLES Ltd. April 3, 1964 [April 6, 1963], No. 13826/64. Heading H4R. A multi-frequency code receiving equipment comprises a number of receivers equipped with speech immunity circuits the outputs from which, i.e. E1 to En, Fig. 1, are fed to a code checking equipment C which gives an output D on receipt of a signal by any, or any particular combination, of the receivers. The output D initiates the operation of two timing devices Z 1 and Z2. Z1 produces an output after a delay tp if the output on D is maintained during this time, and this output X1 via an " OR " gate O provides an enabling input to the " AND " gates U1 to Un and thus passes signals from the receivers to the evaluating device in accordance with the received signals, the " AND " gates being self-holding on their receiver inputs since their outputs are coupled back to the inputs of " OR " gates O to On. When the received signals cease, signal D ceases, but the output X2 of timing circuit Z2 is maintained for a time tv, thus the enabling signal B is maintained for this time. The time tv is arranged to be just less than the minimum possible gap between signals and thus ensures that a gap in the received signal of less than the time tv has no effect on the signals A1 to An passed to the evaluating means and the register. A number of inhibit gates may be provided between the receivers and the " OR " gates O1 to On which gates are blocked by the signal B and thus prevent spurious signals on the receiver outputs from affecting the signals to the register during the evaluation period. The invention is a modification of the code receiving system described in Specification 980,155. |
