GB601289A - Improvements relating to equipment for determining the distance of bodies by means of radio waves - Google Patents

Abstract

601,289. Radiolocation. COSSOR, Ltd., A. C., WILLIAMS, B. C. FLEMING-, and ALLEN, A. Nov. 20, 1945, No. 31257. [Class 40 (vii)] Radiolocation equipment for determining range comprises a transmitter whose frequency is varied linearly with time in each of a plurality of recurrent steps, the rate of change of frequency with time varying progressively from step to step over each cycle of the recurrence period of the plurality of steps and a receiver having means for deriving the difference frequency between the direct and object reflect rays, a circuit responsive to a narrow band of difference frequencies and means for indicating when the rate of change of frequency is such as to produce a difference frequency within said narrow band. A transmitter TX feeds a transmitting aerial TA, and echo signals from a distant object and also a portion of the signal direct from TA, are received on aerial RA and fed to receiver R. The output of TX is frequency modulated in saw-tooth fashion by unit TB1 so that at any instant there will be a difference frequency in receiver R depending on the difference between the direct " Ft " and echo reflected " Fr " signals. For a given rate of frequency variation of the saw-tooth modulation, this difference frequency is proportional to the distance to the object. A second saw-tooth unit TB2 generates a sawtooth wave of 50 cycle per second frequency and period P and this is used to scan cathoderay tube CRO and is also applied to TB1 to cause the rate of frequency variation, that is the slope of the saw-tooth modulation, to be uniformly decreased as shown at TB1 (Fig. 2) although for clearness this does not show the much greater frequency, for example 50 kc.p.s., of the TB1 modulation. During the sweep generated by TB2, the difference frequency, Ft-Fr=Fd, in the output of receiver R for a given object progressively decreases until at a given point in the sweep corresponding to the distance to the object it passes fixed tuned amplifier IF and intensity-modulates the cathode-ray tube to provide a spot GS at a distance D from the origin of the trace corresponding to the distance to the object. It is stated that the period of the saw-tooths generated by TB1 need not progressively increase as shown, but may be kept constant and the frequency variation decreased.