GB585909A - Improvements in or relating to oscillographic methods and apparatus for the observation and/or measurement of recurrent signals - Google Patents

Abstract

585,909. Radiolocation. WHITE, E. L. C. Jan. 29, 1940, No. 1754. [Class 40 (v)] [Also in Group XXXVI] In a cathode-ray oscillograph for simultaneously observing two or more signals of the same wave form and amplitude but differing in timing, modulating means are arranged to vary the intensity of the ray during the production of one of the wave traces so that it may be identified. Apparatus is shown for determining the bearing of an object by the reflection of electromagnetic waves. A transmitter 2 is modulated by a pulse generator 1 so as to radiate a burst of short waves lasting 0.5 millisecond once every 200 milliseconds. The reflected signals are received on three aerials 3, 4, 5, each of which is coupled to its associated amplifier 3a, 4a, 5a. The outputs of those amplifiers are connected in parallel and fed to further amplifying and detecting stages in a receiver 6, the output of which is connected to the input of adjustable delay networks 3b, 4b, 5b. The output of these networks is connected to one pair of deflecting plates 7a of a cathode-ray oscillograph 8a and to one pair of deflecting plates 7b of a cathoderay oscillograph 8b. To the other pair of plates 9a, 9b is supplied a saw-tooth scanning waveform derived from a saw-tooth generator 10 controlled by the pulse generator 1. A generator 11 generates an oscillation having a rectangular waveform and a frequency of 250 cycles per second. This signal is divided by a divider 12 to produce a further oscillation having a frequency of 25 cycles per second which is fed to a device 13 so as to generate three series of pulses having a duration of 40 milliseconds and recurring every 120 milliseconds. The device 13 may comprise a series of commutators on a shaft rotated under control of the output from the divider 12. The series of pulses are arranged to differ in timing by 40 milliseconds. One series of pulses is fed to each of the amplifiers 3a, 4a, 5a so that each channel, comprising an amplifier, delay network and the receiver 6, is rendered operative for 40 milliseconds in succession. Traces corresponding to the waveform of the signals received on each of the aerials 3, 4, 5 appear in turn on the oscillographs 8a, 8b and their timing may be adjusted by the delay networks 3b, 4b, 5b. The cathode rays of the oscillographs 8a, 8b are modulated differently during the successive 40 millisecond periods so that each trace is given a characteristic marking. during the successive 40 millisecond periods so that each trace is given a characteristic marking. This is effected by biassing the control electrodes 14a, 14b so as normally to black-out the cathoderay beam. They are biassed positively so as to increase the beam current to its normal value by means of a biassing signal derived from the devices 11, 13 and supplied either without modulation when the channel 3a, 3b is operative, or modulated by 250 cycles per second pulses in the modulator 16a when the channel 4a, 4b is operative, or modulated by 250 cycles per second pulses in anti-phase in the modulator 16b when the channel 5a, 5b is operative. One trace, therefore, is continuous while the other two are interrupted alternately so that they can be easily identified and brought into coincidence by adjusting the relative delay in the networks 3b, 4b, 5b. The difference in timing between the signals received on the aerials 3, 4, 5 is given in terms of the time delay introduced into the three channels, and the bearing of the reflecting object is then determined. Specification 585,908 is referred to.