Patent GB-601125-A (GB)
Title: Improvements in or relating to radar systems
IPC: G01S13/64
Filed: 1945-04-05
Abstract: 601,125. Radiolocation; pulse circuits. WHITFIELD, H. R. April 5, 1945, No. 8483. Classes 40 (vi) and 40 (vii)] In a pulse radar system signals received from within different elements of range are fed to different channels, in each of which a condenser is charged to the mean signal level obtaining during each interval when signals from the corresponding element of range are being received, so that the successive reception of signals of different amplitudes, due, for example, to the Doppler effect, causes the charge on the condenser to vary and thereby actuates circuits for presenting an indication on a display unit. The echo signals are mixed in the receiver with a locally generated reference oscillation, so that echoes received from moving objects are modulated in amplitude due to the Doppler effect. The output signals from the video stages of the receiver are fed in parallel to ten detecting circuits which operate successively, each circuit admitting signals from a certain element of range, and delivering a signal to a common P.P.I., whenever successive signals vary in amplitude. Figs. 2 and 3 illustrate one detecting circuit of the embodiment described in the Complete Specification. A locking pulse from the transmitter is applied via the point 6, to the control grid of the blocking oscillator valve V3 of the first circuit of the series. The oscillator generates a pulse which is taken from point 9 to synchronize, by its trailing edge, the oscillator of the next circuit, and similarly for all the circuits, so that the ten circuits operate successively. The received signals from the video stages of the receiver are applied at point 8. A large positive potential is applied at point 7 to cause the rectifiers W1, W2, V4 and V5, to be non- conducting except when the oscillator fires, the condenser C15 consequently charging to a level depending on the amplitude of the signal applied at 8. When V3 ceases conducting, the rectifiers also cease conducting and the charge on C15 remains constant until the next locking pulse arrives. If the signals received during the interval determined by the strobe pulse generated by V3 are due to fixed objects, the charge on C15 will remain constant ; if, however, an echo from a moving object is received during the interval, the charge on C15 will vary and a fluctuating output will be obtained across the points 43 and 44 which are connected to the points 46 and 47 respectively of Fig. 3. Point 45 is connected to point 48 so that transformer winding L4 is included in the cathode circuit of valve V7. The output from condenser C15 is amplified by valve V6, the output of which is connected to the grid of V7. In the absence of a fluctuating signal the grid potential is zero and valve current flows to charge condenser C21 to a certain potential, the anode potential of V8 being somewhat smaller. A positive potential is applied at point 49 to cut off the diode V8. When the oscillator fires a positive pulse is applied at the point 48 to cut off the rectifier W4 so that no output reaches the point 49. However when a fluctuating signal is present, the rectifying action of W3 causes the grid potential of V7 to rise to a large positive potential, the cathode potential rising correspondingly. Nevertheless while W4 conducts, the anode of V8 is maintained at a low potential and V8 is still cut off. However, on the application of a positive pulse from the oscillator W4 is cut off, the anode potential of V8 rises and current flows in the diode for the duration of the strobe pulse. Thus an output occurs at point 49 during the strobe pulse period if a fluctuating signal is applied to the valve V6. The outputs from each of the ten circuits are applied in parallel to a video amplifier and thence to a plan position indicator on which the indications from the moving targets are displayed. According to the Provisional Specification, the output of the receiver is applied to the suppressor grid of the blocking oscillator so that the anode potential during the strobe pulse intervals is controlled by the mean signals applied during that period. A condenser is connected from anode to earth, and the anode load comprises a valve which is switched on by the oscillator pulse, so that the charge on the condenser can. alter only during the strobe interval. The condenser output is applied via a rectifier, to a diode switch which allows the strobe pulse to pass to the P.P.I. Specifications 596,649, 596,650, 596,651, 596,657 and 601,124 are referred to.