facsimile empfangsgeraet with a narrow 1 khz band filter for eliminating the influence of leitungsgrundgeraeusche on startimpulse and a device for preventing false starts by stoerimpulse

摘要

769,808. Copying-telegraph receivers. CREED & CO.,' Ltd. May 4, 1955, No.12898/55. Class 40 (3). An arrangement for protecting a facsimile recording apparatus against a false start in response to random signals comprises means for registering a first incoming pulse and generating subsequently, at a predetermined time interval, a testing pulse which in combination with a second incoming pulse starts the recorder, but which cancels the registration of the first incoming pulse if the second incoming pulse is not received in coincidence with the testing pulse. A received signal detected by a filter 2 is passed by demodulator 3 as a positive pulse to the grid 5 of a valve 6 and to the grid of a gas-discharge tube 4 which conducts and cuts off a normallyconducting valve 10. A capacitor 13 begins to charge and after a predetermined time interval a valve 14 conducts and initiates from the secondary winding 22 of a transformer 21 a positive pulse which is applied to the grid of a valve 33 and to the second grid 7 of the valve 6. A little later, due to the higher positive potential of its cathode, the valve 15 conducts and terminates the positive pulse applied to the valves 6, 33. If a second pulse is received via filter 2 and demodulator 3 during the positive pulse determined by the valves 14, 15 and transformer 21, the valve 6 conducts, operating relay 24 which locks up over contact 25 and starts the recorder. Additionally, a signal is sent to the transmitter to suppress the transmission of further start signals. The positive pulse fed from the secondary winding 22 makes valve 33 conducting, and if no further impulse is applied via filter 2 and demodulator 3, the valve 4 is cut off by the negative pulse applied to the plate 8 from the anode resistor 27 and the valve 10 becomes conducting so that the capacitor 13 is discharged and the valves 14, 15 become non- conducting. The arrangement may be extended to be responsive solely to three or more control pulses at predetermined intervals.