GB480150A - Improvements in or relating to printing telegraph systems - Google Patents

Abstract

480,150. Type - printing telegraphy. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. April 22, 1937, No. 11570. Convention date, May 7, 1936. [Class 40 (iii)] The system employs a multiunit equal-interval code in which the ratio between marking and spacing elements is the same for each character, and the receiving arrangements are such that a character is printed only if the received signal consists of the fixed ratio of elements. If an incorrect ratio is received, an " error " character may be printed. The system thus prevents printing in the case of signals mutilated by fading or interference. The code may be of 7 units with 3 (or 4) marking elements providing 35 combinations and using case shift, or it may comprise 8 units of which 3 (or 4) are marking elements providing 56 (or 70) combinations used without case shift. The receiver, Fig. 3, comprises code bars 5 and selector bars 6, one of which can drop into aligned notches 7 in the bars 5 only when the fixed number (3 as shown) of code bars have been shifted to the left. An " error " character bar 22 is selected, if more or less than 3 bars 5 have been shifted, by dropping into a notch N in a bar 20 which is drawn to the left (as shown) to prevent the dropping when a notch in cam 17 comes opposite a projection 19 on bar 20 after movement of 3 bars 5. The shaft of cam 17 is rotated by spring 14 under control of escapement 8, 10 actuated by bar 12 each time a bar 5 is moved to the left. The cam-shaft 9 is restored to normal after character selection by a rack 25 moved to the left by the printer driving mechanism and engaging pinion 22 which drives the shaft through spring 26, a pin 27 on the shaft engaging a stop 28 when normal is reached. The pin 27 by engaging abutment 35 prevents the shaft from being moved more than 4 steps, due to an incorrect signal. When rack 25 moves to the left, pin 29 rides above guide 30 until it reaches spring 31 which deflects the pin so that on the return stroke with the pin beneath the guide, the rack 25 is free of pinion 22, the rack being raised again by a spring 34. In a modification, the escapement shaft 9 and cam 17 are replaced by a relay counting chain which receives an impulse each time a bar 5 is moved to the left. After 3 impulses have been received, a magnet is operated to draw bar 20 to the left to prevent selection of the " error " character bar 22, but if more than 3 impulses are received, the magnet is de-energized to permit selection of bar 22. In this modification, the restoring bar 25 opens the holding circuit of the relay chain.