Patent GB-579154-A (GB)
Title: Improvements in or relating to the detection and/or observation of reflecting objects by means of radiation
IPC: G01S1/02
Filed: 1940-03-29
Abstract: 579,154. Radiolocation. BLUMLEIN, A. D. March 29, 1940, No. 5687. [Class 40 (v)] [Also in Group XXXVI] Apparatus for the observation of an aeroplane or other reflecting object comprises transmitting means for radiating waves having given frequencies f 1 and f2 in successive time intervals and receiving means adapted to receive waves reflected by the object and to heterodyne received waves of frequency f1 and f2 with transmitted waves of frequency f2 and f 1 respectively to a common intermediate frequency. The transmitter comprises a shortwave oscillator 1 coupled to a dipole aerial 2 at the focus of a parabolic reflector 3. The frequency of the transmitted waves is modulated by a modulator 4 comprising a multi-vibrator arranged to generate square-topped pulses at a frequency of 2500 cycles per second. The oscillator 1 and aerial 2 are tuned to 6000 megacycles per second so that each positive and negative pulse has a duration of 200 microseconds and causes the frequency of the oscillator to be changed alternately by plus and minus 10 megacycles every 200 micro-seconds. Means are provided for moving the reflector 3 cyclically within the solid angle which is to be explored The receiver comprises a dipole aerial 5 adjacent to the transmitting aerial 2, a rectifier 6, and an intermediate frequency amplifier 7 which amplifies the 10 megacycle heterodyne signal produced by the transmitted and reflected signals.. Alternatively, a single aerial may be used for transmitter and receiver. The intermediate frequency signals may be integrated to reduce variations in the output of the receiver due to variation in distance of the object. A discriminator circuit 9 is coupled into a stage of the amplifier 7 and arranged to develop a D.C. bias proportional to changes in the intermediate frequency of the received signals. This bias is applied to the multivibrator 4 so as to control the amplitude of the pulses generated by the multi-vibrator and hence the difference between the two frequencies of the transmitted waves. Signals from the output of the detector 8 are fed to the control electrode of a cathode-ray tube 10a so as to control the intensity of the beam. Deflecting means are provided to cause the beam to move across the fluorescent screen of the tube in synchronism with the movement of the reflector 3 so that when the reflector is directed towards a reflective object the intensity of the trace on the screen is varied and a bright or dark spot appears at a point on the screen which is related to the direction of the object. A second cathode-ray tube 11 has its pairs of deflecting plates 12, 13 connected to the output circuits of gain controlled amplifiers 14, 15. A source 16 of sinusoidal oscillations having a frequency of 3 megacycles per second feeds the input circuit of the amplifiers 14, 15, which include valves having their amplification controlled by grid bias. Grid bias for controlling the gain of these amplifiers in opposite senses is provided by a saw-tooth generator 10 controlled by pulses from the multi-vibrator 4. The control electrode of the cathode-ray tube 11 is connected to the output circuit of the detector 8. During a 200 micro-second period between successive frequency changes of the oscillator 1 the oscillations applied to the plates 12, 13 vary in amplitude in opposite senses and cause the beam to trace on the screen of the tube 11 a straight line which rotates through a right angle in 200 microseconds. If waves are received from a reflecting object, the brightness of the trace is modified momentarily after a time equal to the time required for the transmitted waves to travel to the object and return, so that the angular position of the bright or dark line caused by this modification indicates the distance of the object. The bias on the cathode-ray tube may be adjusted so that the trace is normally blacked out and only becomes visible when a reflected signal is received. The distance and direction of the reflecting object may be indicated simultaneously on the same cathoderay tube by superimposing the two deflections for separate indication of direction and distance. The deflection which follows the movement of the reflector 3 is modified so that the mean position of the cathode beam is held fixed for each 200 micro-second period in a position corresponding to the mean angular position of the reflector during that period. The deflecting potentials are derived from a number of contacts associated with the reflector and arranged to feed to the plates of the cathoderay tube potentials related to the angular position of the reflector. The cathode-ray beam then traces rotating lines in successive 200 micro-second intervals about spaced points corresponding to the successive mean angular positions of the reflector 3. On the receipt of reflected waves, inclined bright lines indicate the distance of the object by their inclination and its direction by their location on the screen. The invention may be applied to the navigation of aircraft or ships.