GB605454A - Improvements in or relating to radio-location systems - Google Patents

Abstract

605,454. Radiolocation. GRAYSON, H., and BROWN, D. E. Feb. 28, 1946, No. 5065. Drawings to Specification. (Class 40 (vii)] In a radar system, wherein the Doppler effect is employed to differentiate between fixed and moving targets, reflected echoes of the exploring pulses of radio frequency are mixed with a locally-generated reference oscillation having a predetermined phase relationship with the oscillation of the transmitted pulse. Either the radio frequency or the reference oscillation is derived, one from the other, by the mixing of one with the output of a stable oscillator. The reference oscillation may either comprise a continuous oscillation or an intermittent oscillation persisting after the transmitted pulse sufficiently long to encompass the received echo pulses. In one embodiment of the invention the reference oscillation is generated from an oscillator, the output of which is periodically amplified to produce the exploring pulses, by mixing the output of saidoscillator with the output from the local oscillator of the superheterodyne receiver of the radar system. The reference oscillation which is thus at the intermediate frequency is mixed with the received signals either in the intermediate frequency amplifier or in the second detector. In a second embodiment the output from an oscillator generating signals at the intermediate frequency is mixed with the output of the local oscillator, the resultant signal, which serves as the reference oscillation, being injected into the pulse transmitter to synchronise the oscillation of each transmitted pulse. The reference signal is also injected into the radio frequency stages or the frequency changer of the receiver. In a third embodiment wherein an intermediate frequency oscillator operates as before to control the oscillations of the transmitted pulses, the output of the oscillator serves as the reference oscillation and is injected into the intermediate frequency amplifier or second detector. When echoes from moving targets are being received, the output from the second detector contains a component at the Doppler beat frequency, which is filtered off, amplified and applied to an indicating device such as a loud speaker, cathode-ray tube or tuned reed indicator. Provision may be made for varying the pulserecurrence frequency since the amplitude of the Doppler beat signal of the any particular frequency depends upon its relationship with the pulse recurrence frequency and might in certain circumstances become zero. Strobing may be provided to select one of a number of echo pulses. Specifications 596,650 and 596,657 are referred to.