Patent GB-612834-A (GB)
Title: Improvements in or relating to start-stop telegraphic distortion testing apparatus
IPC: H04L17/14
Filed: 1946-02-14
Abstract: 612,834. Photo-electric control of telegraphic transmitters; testing apparatus for telegraphy. PELLE, P. Feb. 14, 1946, No. 4727. Convention date, Feb. 14, 1945. [Class 40 (iii)] A start-stop telegraphic transmitter which sends predetermined messages for testing the operating margin of a receiver comprises a slotted disc rotating between a light source and a slotted screen, the latter being placed in front of a photo-electric cell. An oscillatorcontrolled motor M (Fig. 1) drives a slotted disc'D at a constant speed' between a light source L and a photo-electric cell C whose output is amplified at A and at B transmits a mark or space to line Lc according to whether the cell C is illuminated or not. A slotted screen R is interposed between the light source L and the disc D which is divided into seven equal sectors (Fig. 2) in six of which are arcuate slots d, and 1 ... 5 each of a radius less than its predecessor. As the disc D rotates, these slots pass in front of the fixed slot R, allowing the cell C to be illuminated and thus sending six space signals to line. The seventh sector a is not slotted and therefore sends a mark or stop signal to line. In order that the characters transmitted may be varied so as to comprise a predetermined message, screens e1 . . . e5 mask the portions of the slot R corresponding to the code slots 1 ... 5 under the control of electromagnets X1 .... X5. The control leads of these magnets are connected to five wipers g1 ... g5 of a multi-bank rotary switch CRo in each position of which predetermined ones of the five coacting contacts are connected to battery. At each rotation of the disc D a brush K energizes a drive-magnet Xo to step the rotary switch CRo and extend battery via wipers g1... g5 to selected magnets X1 ... X5. Each magnet not energized interposes a screen e1 ... e5 between the light source L and the fixed slot R in order that a predetermined character is transmitted. Hence, as the disc D, and the rotary switch CRo continue to rotate, a predetermined test-message is transmitted. In order that the start and stop signals of each successive test message may be progressively distorted, the start slot d is replaced by a diametrically opposite slot d1 which from right to left is composed of progressively longer or shorter elements. A slot R1 allows light from a second lamp L1 to fall on a cell C1 in parallel with the cell C so long as the disc D beneath the slot R1 is slotted. Masking the slot R1 is a supplementary screen es having an aperture l therein equal in width to an element of the start slot d1. As the disc D rotates for the first test-message, the start and stop elements are of standard length. At the end of the message, however, a sixth wiper gs energizes a drive magnet XS via disc contact K and moves the apertured screen es laterally so that a longer element of the start slot d1 is 'uncovered and hence for the next test message the start signal is lengthened and since the start slot allows the cell C1 to be illuminated before the end of the stop signal, the latter is shortened. Subsequent messages are similarly progressively distorted. When the switch CRo reaches, say, its fifth position, battery is connected from selected contacts on a second switch CRn via its wipers, and switch CRo to selected magnets X1 ... X5 in order to transmit. a symbol indicating the degree of distortion present in that message. The switch CRn is stepped on at the end of each message.