Patent GB-316298-A (GB)
Title: Improvements in or relating to high speed printing telegraphs
IPC: H04L27/26
Filed: 1929-07-09
Abstract: 316,298. Soc. Franþaise Radio-Electrique. July 28, 1928, [Convention date]. Type-printing telegraphs. -Each character is signalled by means of a pair of frequencies in combination, one frequency being selected from each of two groups, the members of which are in arithmetical progression. At the receiving station each frequency is translated into a specific current strength and printing is effected by optical projection of the required characters on to a photographic strip. Transmitter. A perforated tape 1 is pulled from left to right, Fig. 1, by the feed - wheel 9 which is actuated through the ratchet 111 at each descent of the transmitting armature 16. A brake-wheel 5 ensures the provision of sufficient slack 4. The tape is so punched that when the magnet 17 is energized and the plunger 8 descends, a pair of impulses of different frequencies are sent to line or wireless by transmitter generators selected from two groups A, B. Twelve transmitters, may be multiplexed by means of distributors, and telephone records may be used instead of perforated strip. Receiver. The impulses received from line or wireless receiver through the transformer 210 are selected by tuned relay systems 10, 20 - - of which one, viz. 80#, is shown in full. According to the relay selected in group A a weaker or stronger a.c. is permitted to pass from the generator 33 through the tapped transformer T1 to the coil 29, and a current similarly regulated by the selected relay in group B passes to the coil 32, while the coil 35 carries constant current. The short-circuited coils 1<1>, Fig. 3, therefore set themselves in a position depending jointly upon the A and B components. The natural period of motion of the parts 1', 5<1> can be adjusted by variation of the output of the generator 33, and its damping is adjusted electrically. The frame 1<1> is universally pivoted and carries a transparent plate 5<1> upon which the alphabet and other characters are inscribed, and is set by the coil 35 so that the required character is optically projected by lenses, a reflecting prism 10<1>, and revolving mirrors 18' individual to the multiplex channels, on to a photographic strip 21'. The projections may also be observed visually. 'The letter plate 5<1> is formed with a blank cross, so that failure, of one component of the signal gives rise to a blank in the record. The illumination may be rendered intermittent, by spark or shutter, to prevent blurring of the record. In modifications an opaque letter-plate 5<1> may be employed, and the resonant relays 10, 20 - - may be replaced by tuning fork or by electrodynamometers each having one coil energized by local current of the desired frequency. The a.c. generator 33 may be replaced by a d.c. source and the moving coils 1<1> by a magnet. Distributor systems.-One transmitter 8, 16, 17 is provided for each of twelve channels, the magnets 17 being energized in succession through staggered contacts on the left-hand distributor drum, Fig. 1. The pairs of alternating currents are sent to line in succession through the staggered contacts on the right-hand distributor drum, these contacts being narrower than the former so that they pick out the middle portion of the signal. At the receiver the signals belonging to different channels are picked out by the mirrors 18' as described above and are recorded either on different tapes or side by side on the same tape, the latter being subsequently cut up. The channels may be allocated alternately to two receivers, the valves of which are alternately disabled by the application of negative grid bias. Or where two transmitters of identical construction are to work diplex, the frequency bands may be separated by the addition of a constant frequency to each member of one of the bands. Synchronous movements.-As the signal combinations occur at regular intervals they can be made by rectification to yield a current of definite low frequency (about 50 or at 600 words per minute). The receiver may be driven by a motor having a commutator for d.c. driving current and also slip-rings to which the synchronizing current is applied.