GB585908A - Improvements in or relating to methods of and apparatus for modifying recurrent signals and applications thereof - Google Patents

Abstract

585,908. Wireless signalling. BLUMLEIN, A. D. Dec. 4, 1939, No. 31445. [Class 40 (v)] Parts of a repeated train of signals are selected at time-intervals coinciding with different portions of the train over successive cycles and are applied to an integrating or " retaining " device to build-up a derived signal having the same wave-form as the whole or part of the original repeated signal. The wave-trains are fed to the integrating device through a valve " switch " of the kind described in Specifications 585,906 and 585,907, the period of the switching then being varied cyclically so as to bring the derived signals into a desired time-relation from which the timeinterval between the original signal-trains can more readily be measured. As applied to the method of " spotting " aeroplanes described in Specification 581,920, repeated trains or " bursts " of signals are radiated from a transmitter Tr under the control of a master pulse-generator PO, which is coupled to the transmitter . through a subsidiary generator PG1 and a delay network Dt to permit the timing to be adjusted. After reflection, say, from an aeroplane, the signals are picked up by three spaced aerials Ax, Ay, Az arranged at the corners of an equilateral triangle, and are fed to receivers Rx, Ry, Rz. Here their original timing is modified by switching or " unblocking " impulses applied to one or more of the valve stages. The timing of the switching impulses is varied cyclically by a pulse modulator PM and a saw-toothed wave-generator SG so as to select different elements of the signal train in successive cycles, and thus to integrate or develop the original form of wave-train, but with new timing. The modified output is then applied to cathoderay tube indicators O1, O2, Od through a " shuffling " device Sh of the kind described in Specification 543,602. The shuffling device produces outputs proportional (a) to the sum SU and (b) to two integrated differences D1, D2 of the signals. D1 and D2 are applied to the horizontal deflecting plates, and SU to the vertical deflecting plates of the cathode-ray tube indicators O1, 02 whilst the indicator Od is fed from the generator SG and by the voltage SO. Any differences in the phasing or timing of the signals reflected back from the aeroplane can be compensated by adjusting the timing of the switching impulses supplied from PM over the delay networks Dd, Dxy, Dx, Dy and Dz. The extent of the adjustment of the network Dd required to restore equal timing accordingly gives an indication of the bearing of the aeroplane or other body under observation. For synchronous timing, a vertical trace is shown on the screen of the cathode-ray tube, whilst any difference in timing is indicated by an inclined trace. An auxiliary search aerial Ats, located at the centre of the main receiving aerials, is used with associated apparatus as a stand-by device to facilitate the setting of the delay circuit Dd. The rate at which the delay network Dd is altered, as the aeroplane under observation moves, is made to develop a voltage which is then used to keep the circuits automatically in tune to any frequency shift in the incoming signals due to Doppler effect. The invention may also be used to minimise the effect of " random " interference as described in Specification 585,907.