| 摘要 |
935,540. Facsimile transmitters. R. HELL. Dec. 28, 1959 [Jan. 3, 1959], No. 44035/59. Class 40 (3). [Also in Group XL (c)] In a facsimile transmitter in which transmission is effected by the switching-on and switching-off of a carrier frequency, the carrier is always gated in the same phase position. The arrangement is such that the carrier is gated in its first passage through zero, and that it comprises at least one full period even in the case of the shortest picture signals to be transmitted. In the arrangement shown, the picture 2 on the rotating drum 1 is scanned by a beam from a source 3 and a photo-cell 6, the output of which is passed by an amplifier 7 and inverter 8 to a flip-flop device 9 which is arranged to be triggered by voltage of a predetermined value derived from black or white portions of the picture 2. Then change-over of the flip-flop 9 operates " OR " gate device 11 which triggers a multivibrator operating at the desired carrier frequency. The output of the multivibrator is differentiated at 15 and applied to a tuned filter 17 which passes the fundamental multivibrator frequency to a gate 19 and line 20. The output of the flip-flop 9 also passes via connection 21 and a differentiator 22 to a switching device 24. producing a voltage pulse for a time duration equal to the period of the multivibrator so that the latter is made operative and the gate 19 held open for a complete carrier frequency period in response to the voltage produced by the shortest picture signal. When the voltage on the line 10 ceases, " OR " gate 11 closes, bringing the multivibrator 13 to rest and effectively shutting the gate 19 so that transmission to the line 20 is immediately discontinued. |
