Patent GB-1466136-A (GB)
Title: Pulse radar apparatus
IPC: G01S13/24
Filed: 1974-06-14
Abstract: 1466136 APC systems HOLLANDSE SIGNAALAPPARATEN BV 14 June 1974 5 July 1973 26598/74 Heading H3A Pulse radar apparatus is provided with a control circuit for the fine tuning of the momentary transmitter frequency f z  to a frequency f zo  which shows an IF difference f o , fixed in sign and magnitude, with the local oscillator (8), Fig. 1, frequency f lo  of the pulse radar apparatus (f o =f zo -f lo ) said control circuit comprising at least a tunable transmitting device, e.g. a Dither magnetron 1 and a servo unit 12 driving said device; an error voltage generator 19 with a switch 36 connected thereto, whereby said generator 19 derives an error voltage (Fig. 4) from the signals supplied by the transmitting device and the local oscillator proportional to the frequency difference |#f| - |f 0 |, where #f=f z -f lo ; an angular position indicator 13, coupled to the shaft of the motor 15 of said servo unit; and a conditional circuit 14 which, with the aid of said indicator, delivers a control signal during the period the transmitting device is active in a defined frequency range comprising the desired frequency f zo , whereby in the presence of the first control signal said switch can be set from its first position, in which the transmitter frequency f z  is controlled through an auxiliary voltage V1, to its second position in which the transmitting device is fine tuned to the desired frequency f zo  by means of said error voltage. The auxiliary voltage V1 is derived from a constant voltage source and with the aid of the angular position indicator, the conditional circuit supplies the first control signal from the moment the motor shaft reaches the position corresponding to the transmitting device assuming the extreme value f zmax , Fig. 5, where |f zmax -f zo | < |f zmax -f lo | until, maximally, the moment the motor shaft position corresponds with the other extreme transmitter frequency. With the aid of the error voltage generator 19 the conditional circuit delivers a second control signal only within a time duration in which the difference value #f is in a defined frequency range (output values -V c  to +V c , Fig. 4) extending on both sides of the difference value f o , said second control signal, in conjunction with the first control signal, effecting the braking of the servo unit motor and the first switch being set from its second position to its first position only in the presence of both the first and the second control signals, the motor being braked with the aid of a tacho generator 43 contained in the servo unit, having its voltage fed back to the motor through a second switch 44 controlled by the simultaneous application of first and the second control signals. The frequency discriminator of the error voltage generator 19 comprises two filter combinations 20/21 and 22/23 of which the output voltages F<SP>l4</SP> are separately detected with opposing polarity, the conditional circuit 14 being provided with a dual comparator 34 thresholds +V c , -V c ) connected to the outputs of the filter combinations and feeding a hold circuit 35 to obtain the second control signal. The angular position indicator 13 comprises a rise detector and a fall detector analysing the rotation sense and momentary angular position of the motor shaft, to deliver two slope-indication signals respectively corresponding with a rising or falling transmitter frequency, the conditional circuit comprising a first bi-stable multivibrator 53, an AND gate 54 and a second bi-stable multivibrator 55, the first bi-stable multivibrator 53 and the AND gate 54 being separately connected to receive the two store indication signals and the second bi-stable multivibrator 55 providing the first control signal. The rise detector and the fall detector comprise a common resolver 46 coupled to the shaft of the servo motor, a phase-sensitive detector 47 connected to the resolver, a common differentiator 49 connected to the phasesensitive detector, and a pair of comparators connected to said differentiator, each of the comparators supplying one of the two slopeindication signals.