GB590944A - Improvements in electrical signalling systems - Google Patents

Abstract

590,944. Radio signalling ; television and copying telegraphy. WESTERN ELECTRIC CO., Inc. Sept. 22, 1944, No. 18180. Convention date, Oct. 5, 1943. [Classes 40 (iii) and 40 (v)] In a signalling system handling cyclicallyrepeated signals, the signal-to-noise ratio is increased by integrating the signals over a number of cycles, the signals being applied as intensity modulation on the trace on a cathoderay oscillograph and the resultant image being projected upon the target of an electron camera which is scanned at a lower frequency to reconstitute the integrated signals. In the application of the invention to a radar system comprising a pulse transmitter 11 and receiver 14<1>, the receiver output is clipped to limit the amplitude of all noise voltages to that of the maximum desired signal, and applied as intensity modulation to the cathode-ray oscilloscope 20. A sweep generator 18, synchronised by the pulse transmitter provides the time base for production of the trace on the screen 22, which may be initiated a controlled time interval after the transmitted pulse or may comprise an expanded section of the total sweep. An image of the superimposed intensity modulated traces on the strip 38 of the screen is focussed on to the mosaic target 41 of the iconoscope tube 40, the deflecting coils 43 of which are fed with a sweep wave synchronised with the sweep of the final oscilloscope 60, the frequency of which is an integral fraction of the sweep frequency provided by generator 18. The charge pattern which accumulates on the mosaic target electrode due to signals is of greater intensity than that due to the noise owing to the random nature of the noise on successive traces, and the signal-to-noise ratio of the stored signals which are removed by the scanning process after a succession of traces is therefore increased. The beam of. tube 20 may be swept in two dimensions to provide a display with bright lines instead of spots corresponding to signals and a cylindrical lens may be employed to condense the two-dimensional field to a linear strip on the mosaic target. The . output from the iconoscope appearing across the signal resistor 53 is amplified at 55 and fed to the deflecting plates 61 of the cathode-ray oscilloscope 60 to produce a type A presentation with the echo signals accentuated relatively to the noise. The invention is stated to be applicable to facsimile or picture transmission, telegraphy and other forms of signalling and the Specification as open to inspection under Sect. 91 describes a facsimile reproduction system in which the received signals are passed through a limiter which clips both positive and negative signals to desired levels, the clipped signals, after passing through a variable gain amplifier being fed to the reproducing device. The original object is scanned and the corresponding signals transmitted a number of times, the gain of the amplifier at the receiver being so adjusted that the superimposed reproductions add to give an image of desired strength with the effects of noise reduced due to their random character in the successive transmissions. It is also stated in the Specification as open to inspection under Sect. 91, that the principle may be applied to any system in which speed of transmission of intelligence is unimportant. Speech may be stored on a tape recorder and repeatedly transmitted the' received message being stored on a synchronously running tape recorder or other suitable integrating device such as the iconoscope. The iconoscope integrator of Fig. 2 may also be employed to produce a single signal train corresponding to the scanning of a single picture line a multiplicity of times. Specifications 474,591 and 477,875, [Group XXXV], are referred to.