Patent GB-611613-A (GB)
Title: Improvements in or relating to apparatus for the location of distant objects
IPC: G01S15/46
Filed: 1945-03-23
Abstract: 611,613. Radiolocation; saw-tooth generating circuits. LAWS, C. A., and WRIGHT, C. S. March 23, 1945, No. 7459. [Classes 40 (vi) and 40 (vii)] Object locating apparatus in which a beam of pulsed electromagnetic or acoustic energy is repeatedly swept through a predetermined angle in elevation, and reception of a reflected echo from an object produces a visible indication on a cathode-ray tube at a position representing the height and range of the object to rectangular co-ordinates, is arranged so that the electron beam of the tube also traces a visible cursor line on the screen in a direction normal to the height co-ordinate the position along that co-ordinate of the cursor line being dependent on a control member from which the height (or depth) of the object from a datum level can be determined when the cursor is adjusted om to the echo indication. A common transmitting and receiving directive antenna A is repeatedly scanned in elevation about mounting M, its instantaneous position being communicated to the vertical time-base generator V.T.B. by shaft S. The transmitter T is modulated by pulse generator PG which also triggers the horizontal and vertical timebase generators H.T.B. and V.T.B. and which switches on the cathode-ray beam at low intensity for the duration of the scan. Received echo pulses are used to intensity modulate the beam as at B. The horizontal range scale R of the cathode-ray tube indicator is linear and the vertical height scale is also made linear by controlling the time-base generator V.T.B. according to the sine of the angle of elevation #. The horizontal scan generator, comprising only that portion of Fig. 2 between the chain dotted lines, receives positive pulses from PG to cancel the normal negative bias on the suppressor grid of V1 so that a negative voltage step is passed to V2 where it is amplified and reversed in phase. It is then fed through cathode follower V3 to the deflection coils L in series with R2. The potential across R2 after phase reversal by V4 is fed back through coupling condenser C4 to the control grid of V1. Thus, the initial fall in potential of the anode of V1 is quickly arrested by the grid going negative and a steady state reached in which the rate of change of potential across L is maintained constant by the controlling action of V1 at a value determined bv the time constant of C4 and R9 and also the current through R9 which is proportional to V, the voltage from potentiometer P1. Different range scales can be obtained by the adjustment of the tapping point on PI. The vertical time-base generator and cursor line producing circuit comprises the whole of Fig. 2; the time-base circuit itself is exactly the same as that used for horizontal deflection with the exception that the potentiometer PI is wound according to a sine law and the previously mentioned shaft S varies the tapping on it according to the angle of elevation of the beam so that the height scale is maintained constant and linear. An alternative control valve V5 is provided in a similar circuit and in parallel with V1 and one in twenty pulses are supplied to it instead of to V1. V5 passes forward signals to V2, V3, L, V4 and also to V6 in parallel with V4. The anode of V6 fed through R14 is directly connected to grid g1 of the double triode V7, the other grid of which is maintained at an adjustable potential by means of R16 and the tapping on potentiometer P2. Normally, g2 is less positive than g1, but when V5 is made conducting, g1 becomes less positive and current flows in the second triode section, whereupon a2 falls in potential and so does the grid of V5 connected to it through C6. The time constant of C6, R13 is made much larger than the scan period so that once the current in the coils L has reached a certain value, which depends on the setting of P2, it remains constant for the duration of the scan. P2 is provided with a calibration so that when the horizontal trace produced is set over the echo trace the height may be read. For ranges where earth curvature has to be taken into consideration a suitable correction voltage waveform can be applied through V8 to produce the required curvature of the cursor line. Minor variations of the circuit are described; for example, omitting V4, V6 and R2 and deriving voltages for g1 and C4 from a dropping resistor in the anode circuit of V3.