Patent GB-592441-A (GB)
Title: Improvements in pulse echo distance measuring or radar devices
IPC: G01S1/02
Filed: 1944-06-30
Abstract: 592,441. Radiolocation. WESTERN ELECTRIC CO., Inc. June 30, 1944, No. 12545. Convention date, Sept. 5, 1941. [Class 40 (v)] Relates to pulse echo distance measuring systems and more particularly to pulse radar systems in which the range is determined by generating reference pulses and transmitter trigger pulses of the same pulse recurrence frequency (PRF) and phase shifting either the reference or the trigger pulses to bring the reference pulses into coincidence with the echo pulses. According to the invention the pulses of variable phase are derived from a periodic source having a repetition frequency ("phasing" frequency) higher than the recurrence frequency of the system and the phase shifting is performed in the " phasing " frequency stage whereby a larger phase shift is required resulting in a more accurate adjustment. In Fig. 1 the radar transmitter 18 is triggered directly by a pulse generated at 14 from the 3933 c/s. oscillation produced by the master oscillator 10. Frequencies of the fundamental and 25th harmonic respectively are selected by the filters 20, 22 and passed through the parallel paths comprising phase shifters 24, 28, amplifiers 30, 32 and pulse generators 34, 36 to give a series of broad pulses 104, Fig. 7, of fundamental PRF and a series of narrow pulses 102 of phasing frequency PRF. The phase shifters 24 and 28 are geared together through the 1: 25 step-up gearing 26 so that the coincident pulses 102, 104, shown in Fig. 7, will remain coincident throughout the total phase-shift range and the narrow pulse 102 can be selected by applying the two sets of pulses to a blanking amplifier 38 biassed to a cut-off level 103, Fig. 7, and fed as the variable-phase reference pulse to one Y plate of the cathoderay tube 40, the echo pulses from the receiver 44 being applied to the other. The time-base sweep voltage corresponding to the whole or a selected portion of the range is generated in the sweep circuit 42 and synchronised from the transmitter trigger pulse. Since a complete rotation of phase shifter 28 corresponds to a small change of range, the range indicator 27 is geared to the phase shifter to measure the total phase shift, i.e. complete and fractional rotations, which may be indicated directly in range. In a modification, Fig. 8 (not shown), a high frequency, 100 kc/s., master oscillator is used, the lower frequency determining the PRF of the system being obtained by a frequency divider and in Figs. 3 and 6 (not shown) the phase shifted pulse is used to trigger the transmitter and the time-base circuit, the direct pulse being used as the reference pulse. Fig. 2 shows an embodiment of the invention using a master oscillator 50 of phasing frequency 123 kc/s. and a single phase shifter 28. The phase-shifted oscillation is converted into transmitter trigger pulses of lower PRF by the frequency divider 53, pulse generator 35, blanking amplifier 54 and pulse generator 36 and the unshifted oscillation is converted into reference pulses of fundamental PRF by similar circuits 52, 37, 51 and 34. In a modification, Fig. 4 (not shown), the pulse generators 34 and 36 are connected in front of the blanking amplifiers 51 and 54 and in Fig. 5 (not shown) pulses of lower PRF are obtained from pulses of the higher frequency by pulse counting circuits. In the embodiments described, the PRF of the system and the phasing frequency are harmonically related but this is not an essential feature and a device may be used such as described in U.S.A. Specification 2,234,587 for deriving two unharmonically related frequencies from a single source. Specification 477,875, [Group XXXV], also is referred to.