GB625484A - - Google Patents

Abstract

625,484. Radiolocation. SUBMARINE SIGNAL CO. Nov. 9, 1945, No. 29935. Convention date, July 29, 1940. [Classes 40 (v) and 40 (vii)] [Also in Group XXXVIII] In a reflection-type ranging system using radio or compressional waves, the frequency of the signal transmitted during the recurrent periods a-b, Fig. 1, is varied linearly according to the curve 2, Fig. 1B, and the tuning of the receiver during the later recurrent periods c-d is varied in an inverse manner as shown in the curve 4 so that reflected energy having a transmission time intermediate between b-c and a-d is passed by the receiver, the range being a function of the instantaneous frequency of the receiver at the time of reception. Since the longer ranges, e.g. y, are given by the low frequencies and the shorter ranges, e.g. x, by the high frequencies, the amplitude of the transmitted signal and the receiver gain are varied exponentially as shown respectively in Figs. 1C and D in order to compensate for the increased attenuation of the longer range reflections and reduce the effect of spurious short range reflections. In Fig. 2 (not shown), the transmitted signal is produced by varying the frequency of a master oscillator as shown in Fig. 1A and applying the output to the transmitter through a blocked amplifier which is rendered operative during the period a-b, its gain being varied according to Fig. 1C. The received signal is heterodyned with the master oscillator frequency which is constant during the reception period c-d, giving a beat frequency F the instantaneous value of which as heard by the operator and indicated on a meter is proportional to the range of the signal being received at that time. Since the range is also a function of the time of reception of the signal it may be indicated by a rotating disc carrying a neon light which is illuminated by the received signal. The linear frequency variation shown at A could be approximated by a single harmonic function or a combination of straight line and exponential functions and may be produced by mechanical means or by electrical means such as disclosed in U.S.A. Specification 1,830,166, or by controlling the resonant element of a klystron when very high frequencies are employed in which case a klystron could also be used in the receiver. Fig. 3 (not shown), illustrates a system adapted for acoustic and supersonic ranging in which the tuning and gain of the transmitter and receiver are controlled by mechanically ganged rotating condensers and biassing potentiometers. Alternatively the amplitude variation of the transmitted signal may be produced by using a transmitter with a peaked resonance curve, Fig. 4 (not shown), such as disclosed in U.S.A. Specifications 1,167,366 and 1,604,693.