Patent GB-606110-A (GB)
Title: Improvements in or relating to ultra-high frequency object detecting systems
IPC: G01S13/58
Filed: 1944-08-03
Abstract: 606,110. Radiolocation. SPERRY GYROSCOPE CO., Inc. Aug. 3, 1944, No. 14872. Convention date, Sept. 7, 1943. [Class 40 (vii)] In a radiolocation system for detecting moving objects by means of the Doppler effect, such as that disclosed in Specification 493,708, the range of velocities over which the apparatus is effective is extended by means of one or more Doppler note translator circuits which transpose to the most sensitive portion of the audio range, those Doppler beat notes which are above or below that range. Transmitter 11, Fig. 1, radiates continuous waves of frequency f from aerial 17, the reflected waves of frequency f<1> from a moving target 14 being received on a common or separate aerial 19 and mixed with direct radiation from the transmitter in the receiver 13, comprising mixer 21, local oscillator 22, I.F. amplifier 23, detector 25 and audio amplifier 26, to produce the Doppler beat note f-f<1>. If the Doppler note is in the most sensitive audio range of approximately 200 c/s. centred on 1000 c/s., it may be fed to headphones 28 via a high-pass filter 55, cutting off at 200 c/s. to reduce noise. If the Doppler note is below the audible range, the head-phones may be connected by switch 46 to the output of a balanced modulator 31 which is fed with the Doppler note, through a low-pass filter 51 cutting off at 200 c/s., and a 1000 c/s. carrier from oscillator 29. If the Doppler note is above the audible range, the telephones are connected through switch 46 to the output of balanced modulator 53 which is fed with the Doppler note through high-pass filter 52, which cuts off at about 1000 c/s. and a 5000 c/s. carrier from oscillator 54, the lower resulting side-band. being then in the audio range. Modulators 31 and 53 may be replaced by a single modulator, suitable switching being employed to connect the appropriate carrier oscillator and filter in circuit. In a modified arrangement, Fig. 3, for detecting objects producing Doppler notes within the effective audio range and also high-speed objects producing Doppler notes of, say, 4000 c/s., the Doppler frequency output from amplifier 26 is passed to the telephones 28 through a single modulator 31 fed with a 5000 c/s. carrier from oscillator 54. High-pass filter 55, cutting off at 200 c/s., substantially eliminates noise and is followed by a low-pass filter 56 cutting off at 4500 c/s., the receiver or amplifier 26 alternately being arranged to pass frequencies between 200 and 4500 c/s. Doppler notes of the order of 4000 c/s. are prevented from passing directly to the telephones by a low-pass filter 57 which cuts off at 2500 c/s.; while the lower side-band which is produced in modulator 31 and rises in frequency as the Doppler note falls, is audible. When the Doppler note falls below 2500 c/s., it is directly audible in the telephones, but the beat frequency produced by the modulator is eliminated by filter 57. In a further modification, Fig. 4 (not shown), a carrier frequency of 2500 c/s. is used so that the Doppler note from high-speed objects produces in the telephones a translated tone which falls in frequency as the Doppler frequency diminishes. Doppler frequencies of less than 2500 c/s. pass directly through the modulator, but the simultaneous production of a beat note indicates that the true Doppler frequency is below 2500 c/s. and not above. Other carrier oscillators of different frequencies may be simultaneously connected to the modulator 31 to enable audible beats to be produced whatever the value of the Doppler frequency.