GB581160A - Improvements in and relating to electrical range finders - Google Patents

Abstract

581,160. Radiolocation. NASH & THOMPSON, Ltd., NASH, A. G. FRAZER-, and WHITAKER, A. Nov. 8, 1939, No. 29663. [Class 40 (v)] The range and rate of change of range of an object, such as an aircraft, are determined separately. The frequency of an oscillator 1, Fig. 1, is modulated by a saw-tooth modulator 2 and the output is fed by a transmission line 3 to a dipole aerial 4 mounted in a reflector 5. The signal after reflection from the distant object is received on a dipole aerial 7 and passed by a transmission line 8 to a receiver 9. A small proportion of the radiated signal from the oscillator 1 is byepassed by a coupling 10 direct to the receiver 9. This produces a difference frequency which depends both on the velocity of the target in the line of sight and on its distance, and is fed to one input circuit of a meter unit 11. A second oscillator 12 generates a constant frequency which is transmitted to a dipole aerial 14. After reflection, the signal is received on a dipole aerial 16 and transmitted to a receiver 19. A small portion of the transmitted oscillation is passed directly to the receiver 19 through a coupling 20. The output of the receiver contains a difference frequency which depends only on the velocity of the target in the line of sight, and is fed to one input circuit of the meter unit 11. The four directional reflectors 5, 6, 15, 17 have parallel axes and can be turned together in any desired direction. The meter unit is shown in Fig. 2. The difference frequencies from the receivers 9, 19 are fed to frequency meters 24, 23 respectively, these meters developing a D.C. output which depends on the frequency but not the magnitude of the input. The outputs of the meters 23, 24 are fed to a network comprising D.C. indicators 25, 26 and a resistance 27. The output of the meter 23 is fed through the indicator 25, which is calibrated in line of sight velocity or rate of change of range. The output of the meter 23 also passes in part through the indicator 26, through which also passes in the reverse direction a part of the output of the meter 24. The output impedances of the meters 23, 24 and the impedances of the indicators 25, 26 and the resistance 27 are so chosen that the component of the current from the meter 23 passing through the indicator 26 is equal and opposite to the part of the component of current from the meter 24 passing through the same indicator and representing the rate of change of range component of the output of the meter 24. The indicator 26 may then be calibrated directly in terms of range.