Improvements relating to radio-echo systems for measuring rate of approach or receding of moving objects

Abstract

Abstract 585,988. Radiolocation. STANDARD TELEPHONES & CABLES, Ltd., CHATTERJEA, P. K., and HOUGHTON, L. W. Oct. 10, 1941, No. 13078. [Class 40 (v)] A system for measuring the relative velocity of a moving object with respect to a stationary or moving transmitter location giving a continuous direct indication, comprises an antenna arranged to transmit waves towards the object and to pick up waves after reflection therefrom, means for separating the beat frequency produced in the aerial circuit between the transmitted and received waves, and means for indicating the beat frequency. An oscillation generator consisting of a valve 1 is caused to oscillate at a frequency determined by a tuned circuit comprising an inductance 5 and condenser 6 connected between the anode 2 and grid 3. High-tension voltage is applied to the anode through an inductance 10, forming the primary of a transformer 9, and a high-frequency choke 12 and a portion of the inductance 5 determined by a variable tap. A condenser 13 is connected between the junction of the inductance 10 and choke 12 and earth, the cathode 4 also being connected to earth. The output from the oscillator circuit 6, 5 is fed to an antenna 14 by means of a coupling coil 15 inductively coupled to the inductance. The antenna 14 also picks up the reflected waves and feeds them to the inductance 5, where they are heterodyned with the generated oscillations so as to give a resultant beat note whose frequency depends on the relative velocity between the transmitter and the reflecting object. This beat note is obtained in the secondary winding 11 of the transformer 9. Voltage of beat note frequency is then fed through an amplifier and amplitude limiter to a frequency discriminating circuit whose output current or voltage is proportional to the input frequency. The resulting output is applied to a meter 17 calibrated in terms of " rate of approach." Indication as to whether the object is approaching or receding may be obtained by using a frequency balanced circuit fed directly or through a coupling connected across the points XX. Alternatively, a pair of filters whose frequency - voltage characteristics slope in opposite directions and cross each other at the transmitted frequency may be fed in parallel from the tuned circuit 5, 6. The outputs from. the filters may be fed in opposite directions through resistances in series having a voltmeter connected across their ends. This indicates whether the received frequency is above or below the transmitted frequency and hence whether the object is approaching or receding.

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