Patent GB-620568-A (GB)
Title: Improvements in radio location and detection arrangements
IPC: G01S13/34
Filed: 1945-07-25
Abstract: 620,568. Radiolocation. RUST, N. M., and PARTINGTON, G. E. July 25, 1945, No. 19102. [Class 40 (vii)] In a frequency-modulated radar system, wherein reflected waves are mixed with the transmitted waves to produce beat-frequency signals, the beat-frequency signals are applied through a fixed-tuned frequency selector to an indicator and the rate of change of transmitted frequency is varied so that the selector passes in succession echo signals received from reflecting objects at different ranges. The echo signals may be displayed on a cathode-ray tube, the range deflection of which is varied in synchronism with the rate of change of transmitted frequency so that the ranges of the various echo producing objects may be deter. mined. An aural indicator or a meter may be used in place, of a cathode-ray tube. A generator. 3 produces a symmetrical triangular waveform (a) which is mixed with a sawtooth waveform (b), produced by generator 5, in control amplifier 4 so that the signal applied to transmitter 6 is as shown as (c). The signal transmitted by 6 is then frequency-modulated in accordance with (c). (Alternatively the wave. form (a) may be frequency-modulated by waveform (b), this signal being used to modulate the transmitted frequency.) The reflected signals are received at 7 where they are mixed with signals from 6 applied through the variable coupling device 8. The receiver 7 may be rendered inoperative when the sawtooth wave changes slope. The demodulated output of the receiver is applied to a fixed frequency selecting device 9 and thence to a cathode-ray tube display unit 10, the horizontal sweep of which is controlled by the waveform (b) from generator 5. The beat-frequency produced by a reflected signal being proportional to the range and to the rate of change of transmitted frequency, which varies on account of the form of the modulating signal (c) (or its frequencymodulated counterpart), a signal from a given range will be passed by the device 9 when the waveform (c) has reached a certain state corresponding to a certain phase angle of the waveform (b), and therefore an indication will be produced on the cathode-ray tube indicative of the range. In order to provide a linear range scale instead of the one illustrated, which closes up towards the longer ranges, a distorting device may be inserted between either 4 and 5 or 5 and 10 so that either the waveform (c) is suitably distorted or the rate of sweep on the cathode-ray tube is suitably varied. The band-width and/or gain of the device 9 may be made variable with range so that uniform discrimination and sensitivity may be obtained. Also, if desired, a manual control may be incorporated into the system so that any particular target may be investigated more closely. A P.P.I. may be used in place of the A-scan described. The Provisional Specification describes also a system wherein each complete cycle comprises a single frequency sweep over a wide band, the rate of change of frequency varying continuously during the sweep. Thus, it may be arranged that echoes from near objects are passed by the selective-device at the beginning of the cycle and from distant objects at its end. The horizontal sweep of the cathode-ray tube is derived from the frequencysweep control waveform. Specifications 581,162 and 594,765 are referred to.