| 摘要 |
935,294. Code telegraphy. WESTERN ELECTRIC CO. Inc. Aug. 3, 1961 [Aug. 29, 1960], No. 28269/61. Class 40 (3). [Also in Group XL (c)] In a circuit responsive to pulse signals above a predetermined threshold level, the threshold level is set to one of two states depending whether or not a pulse has been received during the immediately preceding time interval. The invention enables more positive detection of the presence or absence of pulse signals in the presence of noise in unipolar or bipolar pulse code systems wherein each pulse occurs during a definite time period or " slot." The pulse signals are fed to the grid of valve T1 which is normally biased off by current in resistors 16, 17 and valve 12. If the signal is sufficiently large, T 1 will be made conductive, reducing the anode current of T 2 and providing a pulse on output lead 14. The pulse at the anode of T 1 is delayed at 13 by half a slot period before being used to cut off the anode current of valve 12 so that the threshold level is increased during the next time slot. Unipolar to bipolar pulse converter.-Fig. 9 shows the invention applied to a repeater of the type in which the polarity of alternate pulses is reversed (see Specification 935,293). Clock pulses at the basic repetition frequency are derived from the unipolar input signals by amplifier 74. The unipolar signals are fed in anti-phase to a pair of AND gates comprising diodes 110, 112; 114, 116 controlled by clock pulses from amplifier 74. The blocking oscillators 103, 104 can only operate when a negative pulse of amplitude greater than the threshold level at line 21 passes the appropriate AND gate to the base. The blocking oscillators thus operate alternately so that alternate pulses derived from the output transformer are reversed in polarity. The output pulses are delayed at 23 and fed to NPN transistor 25 and PNP transistor 24 which control the threshold level at line 21 in dependence on whether or not a pulse has been present in the preceding time slot. |
