Patent GB-669258-A (GB)
Title: Improvements in or relating to radio tracking systems
IPC: G01S13/68
Filed: 1950-08-18
Abstract: 669,258. Automatic control systems. SPERRY CORPORATION. Aug. 18, 1950 [Aug. 19, 1949], No. 20525/50. Class 38 (iv). [Also in Group XL (c)] In a radio tracking system of the kind in which radio pulses are transmitted by a rotating dipole 3 and are received after reflection from a remote object and in which the antenna system is automatically directed towards the object by servomotors 28, 47, range-measuring apparatus 31 provides an output signal inversely dependent upon the ranges for varying the gain and/or frequency response of the servomotor system. The arrangement ensures that the servomotors respond at high rates and accelerations to the quickly-changing signals at low target ranges and' vice versa. General. As shown in Fig. 1, the radio tracker, which is preferably of the type described in Specifications 621,485, 635,821, [Group XL (c)], and comprises dipole 3 rotated by a spin motor to provide a conical sweep with respect to the axis of the reflector by U.H.F. pulses generated by transmitter 2, the pulses reflected from the object having a time lag dependent on the range of the object, and measured by the range circuit 31 associated with the transmitter 2 and receiver 11. The spin motor of the dipole 3 also drives two generators 9 which provide 90 degree phase displaced reference voltages for the azimuth and elevation-detectors 20, 21 which control the servomotors. Sinusoidal signal voltages corresponding in intensity to the reflected pulses as produced by the conical sweep are supplied by the receiver 11 to the detectors 20, 21 and compared with the reference voltages to derive error voltages proportional to the azimuth and elevation components of the object with respect to the spin axis of the dipole. The error voltages are applied via potentiometers 37, 38 and amplifiers 24, 41 to the servomotors 28, 47 which are of the Ward-Leonard type and effect the tracking of the antenna. Damping of the servomotors is effected by generators 32, 48 which through networks and potentiometers 95, 100 feed back into the amplifiers 24, 41. The over-all gain of these servomotor systems is controlled in accordance with the range of the object by the device 31 which adjusts the potentiometers 37, 38 and thus the inputs to the amplifiers. Portions 80, 81 are provided at the extremities of the potentiometers to provide constant signal level when the tracked object is outside predetermined limits of range. Similarly the damping signals are varied in accordance with range signals by adjustment of the potentiometers 95, 100. Range measuring circuit, Fig. 4. This Figure shows only the azimuth servomotor, the control of the elevation servomotor being similar. The signal voltage output which depends on the position of the reflected pulses relatively to the transmitted pulses, operates a motor 115 so as to adjust the phase-shifting network 121 until zero signal condition is obtained, e.g. when the reference pulses derived from the transmitter are shifted so as to centre the received pulses relatively thereto. The received pulses are applied to a valve 119 and the transmitted pulses to a valve 122 via the network 121 the valves 119, 122 co-operating with valves 124, 125 to produce differential voltages across resistors 140, 142 at terminals 150, 151 and thus a resultant voltage which is a measure of the phase difference between the pulses and hence the range of the object. The differential voltages appearing at the terminals 150, 151 are converted in valve 157 into a voltage which varies in one direction or the other with respect to earth and controls a phase inverter stage 163, 164 of the modulator 170, 171 and amplifier 174, 175 which supplies the field windings 176, 177 of the motor 115. Hence the motor 115 is operated both in direction and rate to effect range tracking of the target and its displacement is a measure of the range. Variable frequency response. The output of the potentiometers 37, 38, Fig. 1, may be supplied to the servomotor amplifiers via integrating networks and these networks may be varied simultaneously with the potentiometers to alter the time constant and thereby the frequency response of the amplifiers. Such network may comprise a variable resistance and a condenser. Modified arrangements. Instead of varying the over-all gain of the system continuously as in Figs. 1 and 4, the gain may be varied step-bystep by relays controlled by the output of the 'range measuring circuit and arranged to switch fixed resistors into and out of the biasing circuit of the servomotor amplifier. Specification 635,478 also is referred to.