Patent GB-817158-A (GB)
Title: Radio distance measuring system
IPC: G01S13/70
Filed: 1956-08-17
Abstract: 817,158. Pulse radar. STANDARD TELEPHONES & CABLES Ltd. Aug. 17, 1956 [Aug. 29, 1955], No. 25218/56. Class 40 (7). [Also in Group XXXVII] Relates to an automatic-ranging pulse radar in which the timing of two contiguous " early " and " late " gate pulses relative to the transmitted pulse is controlled by a generator producing a pulse whose duration is controlled by an electric motor which is controlled by " early " and " late " coincidence circuits responsive to the gate pulses and the echo pulse such that the timing of the gate pulses is continuously varied (i.e. " search " mode) until the echo pulse coincides with both gate pulses and is then automatically controlled to maintain this condition (i.e. " track " mode). According to the present invention if the echo fades while the system is in the " track " mode it will automatically change over to the " search " mode after the elapse of a predetermined memory period. The invention is described as applied to a secondary radar system using coded interrogating and reply pulses. As shown, a phantastron 31 triggered by a transmitter trigger pulse applied over a lead 28 produces an output pulse 32 whose duration is controlled by a D.C. voltage applied to the cathode of a valve 30 from a potentiometer 69 controlled by a motor 61. The trailing edge of the pulse 32 initiates in a pulse generator 34 the " early " gate pulse 35 whose trailing edge initiates in a pulse generator 38 a " late " gate pulse 39, and the gate pulses 35 and 39 are applied to the screen grids of the " early " and " late " coincidence pentodes 37 and 41 respectively, the decoded reply signals being applied over a lead 8a in parallel to the control grids of the pentodes 37, 41 whose outputs are coupled by transformers 42, 42a respectively to triodes 44, 45. A combined output from the coincidence pentodes 37, 41 is applied through an amplifier 50 and transformer 51 to a search/track control valve 54 and a " memory " valve 55, the time constant of the grid circuit of valve 55 being greater than that of the grid circuit of valve 54. In the absence of any output signals from the coincidence pentodes 37, 41 the valves 44, 45, 54 and 55 are conductive so that relay coils 46, 47, 56 and 57 connected in the respective anode circuits thereof are energized and the associated armatures 46b, 47b, 56a and 57a are in the positions shown thereby connecting the terminals 61a and 61b of the D.C. motor 61 between a positive voltage supply and earth causing the motor to vary the potentiometer 69 such that the duration of the pulse 32 is progressively increased. When the late gate pulse 39 coincides with a reply pulse, the resultant output from the coincidence pentode 41 cuts off valves 45, 54 and 55 thereby de-energizing relays 47, 56 and 57 to change over armatures 47b, 56a and 57a thereby connecting the terminal 61b of the motor 61 to earth via armature 56a, contact 56c, armature 47b and contact 47d. The continued rotation of the motor 61 further increases the duration of the pulse 32 and when the reply echo pulse coincides with both the early and late gate pulses 35, 39 the resultant output from the pentode 37 cuts off the valve 44 thereby deenergizing the relay 46 so that the terminal 61a of the motor 61 is now connected to earth via armature 46b and contact 46d and the motor stops. If the timing of the echo pulse changes so that it coincides only with the early gate pulse, the relay 47 becomes energized thereby connecting the motor terminal 61b to the positive supply causing the motor to rotate in the opposite direction and re-establish the equilibrium condition; the corresponding range is indicated by a counter 20 driven by the motor 61. If after locking on to a reply pulse, the reply pulse then fades, valves 44, 45, 54 and 55 become conductive and the relays 46, 47 and 56 are immediately energized, but due to the long time-constant of the grid circuit of valve 55 the energization of relay 57 is delayed thereby delaying the energization of the motor 61 so that the gating pulses remain fixed for a predetermined memory period after which they are progressively displaced to effect searching. In order to reduce hunting by the motor 61, the relays 46 and 47 have additional armatures 46a, 47a which in the de-energized condition of the relays, couple resistors 72, 73 into the input circuits of valves 44 and 45.