Patent GB-587592-A (GB)
Title: Improvements in radar devices
IPC: G01S1/02
Filed: 1944-09-29
Abstract: 587,592. Radiolocation ; valve circuits. WESTERN ELECTRIC CO., Inc. Sept. 29, 1944, No. 18736. Convention date, Oct. 5, 1943. [Class 40 (v)] [Also in Group XXXV] Relates to improvements in pulse radar systems such as disclosed in Specification 582,228, in which the range is determined by bringing a range marker pulse into alignment with an echo pulse. According to the invention, a-potential changing at a predetermined rate is applied to the grid of a valve and a series of timing pulses are applied to the grid or the cathode, the potential of the cathode being varied to select one of the timing pulses for use as a range marker. In Figs. 1 and 2 a pulse a from the generator 15 controlled by the master oscillator 14 triggers the transmitter 10, initiates the time-base waveform b in the sweep circuit 35 and triggers the single-stroke multi - vibrator 16 to give a square wave c, the negative portion 17 of which produces a wave train d in the feed-back " ringing " oscillator 20 which is applied to the phase shifter 21. The phase-shifted output e is amplified and converted into a a series of alternate positive and negative pulses f in the generator 22 and fed to the grid of a selector valve in the circuit 23 together with an exponentially rising voltage g36 produced by feeding the square wave c from the multivibrator 16 to initiate the charging of a condenser in the selector circuit. The cathode potential g37 of the selector valve is controlled by a potentiometer ganged to the phase shifter, whereby a selected positive timing pulse 26 makes the selector valve conductive to give a negative pulse in the anode circuit which is shaped to a sharp pulse i26 or step wave and fed to a Y plate of the cathode-ray tube 30 as a range marker which is brought into alignment with an echo pulse j by rotating the handle 126 controlling the ganged phase shifter and potentiometer, the corresponding range being read off the counter 32. The two pulses may then be maintained in alignment automatically using a known form of control apparatus. The resistance of the potentiometer should vary non-linearly to correspond to the exponential change of the condenser. A fixed delay circuit is inserted between the receiver 13 and the signal plate of the cathoderay tube 30 to compensate for the minimum delay of the ranging circuit so that the ground pulse is visible on the trace. Alternatively, the selected pulse may initiate the time base and a pulse delayed a fixed amount with respect to it used as the ranging pulse. Thermionic valve circuits. Figs. 3, 4, 5. The single-stroke multivibrator 16 is similar to the corresponding circuit 16 in the Specification referred to except that the grid of the first valve is returned through a resistance R86 to H.T.+ to prevent operation by small extraneous pulses. The timing wave generator 20 comprises a temperature - controlled, screened, tuned circuit L2, C13 in series with the normally conductive triodes V2.1 and V2.2 which are cut off by the negative portion 17 of the square wave C from the multivibrator, thereby shock-exciting the tuned circuit to produce a wave train d. The top end of the tuned circuit is earthed as regards A.C. by the condenser 682 and the bottom end is coupled to the grid of the following valve V3, the cathode of which is backcoupled to the mid-point of L2 through resistance R14 to maintain the amplitude of the wave train constant, the correct amount of feed-back being obtained by adjusting R14. The anode-cathode path of valve V2.2 is shunted by the variable condenser C14 to compensate for variations in electrode capacity due to any replacement of the valve. The primary purpose of V3 is to produce two outputs of equal amplitude in phase quadrature, the principle being discussed with respect to Figs. 6-8 (not shown) and Fig. 9. It is shown that the required outputs are obtained from the anode and cathode of the valve in Fig. 9 when L / Rk = RpC = I / @O and that no transient disturbances are produced by the sudden application of a wave train as in the simple R-C phase quadrature circuit. In the actual circuit of V3, the cathode resistance Rk is composed of R15, R19 and twice R14 in parallel, the doubling effect of R14 being due to the impedance of the tuned Circuit L2, C13, and the anode and cathode voltages are adjusted to exact quadrature by the trimming condenser C16, the two reactances being balanced by the variable condensers C21 and C22. , The two outputs are each phase split by the valves V4.1 and V4.2 and the four-phase displaced potentials applied to the four stators 81-84 of the phase shift condenser as described in Specification 582,228, the phase shifted output e being amplified in an amplifier comprising V5 and V6 also described in the Specification referred to. The amplified output is ''squared off" in the distorter amplifiers V7 and V8, V7 being normally biassed to cut-off by the positive potential applied to its cathode from the potential divider R47, R48 and the grid of V8 being returned to H.T, + to make it normally conductive. The output is differentiated by the short time constant circuit R61, C36 and the resultant pulses f applied to the grid of the selector-valve V10 together with an exponentially rising voltage g36 produced by cutting off V1.2 by the negative square wave from the multivibrator 16 and thus allowing the parallel condensers C38 and C39 to charge through the resistance R62. The cathode potential g37 of V10 is controlled by the exponential potentiometer R67 so that a selected positive pulse g26 makes V10 conductive. Alternately, the timing pulses may be applied to the cathode, a negative pulse being then selected. The output from the valve V10 is applied through condenser C41 to the grid. of valve V9.2 so that when valve V10 is rendered conductive by the selected pulse. condenser C41 is rapidly discharged and valve V9.2 is cut off by the sudden decrease in its grid potential. Due to the long time constant of the charging circuit R64, C41, R71, the valve V9.2 remains cut off for the succeeding portion of the " active " interval 17, Fig. 2 (c), of the trigger cycle so that none of the timing pulses following the selected pulse 26 affect the anode voltage of valve V9.2. The positive waveform at the anode of valve V9.2 thus has a steep leading edge which is differentiated by the short time-constant circuit C44, R74, the resulting sharp positive pulse appearing at the .anode of the heavily biassed valve V11 as a negative pulse, the sharpness of which is improved by the positive feed-back connection between the screen of VII and the grid of V9.2. The negative pulse is then applied as the marker pulse to one Y plate of the cathoderay tube through the transformer T1.