Patent GB-627982-A (GB)
Title: Methods and apparatus for radio echo ranging
IPC: G01S19/46
Filed: 1946-06-27
Abstract: 627,982. Radiolocation ; keying carrier frequencies. SUBMARINE SIGNAL CO. June 27, 1946, No. 19218. Convention date, March 20, 1941. [Classes 40 (v) and 40 (vii)] In a radio echo ranging system, the outgoing pulses are generated by an oscillator which is triggered by the discharge voltage of a condenser in a condenserresistance combination connected in the output circuit of a periodicallyoperated gaseous discharge tube. The arrangement is such that the gaseous discharge tube operates within fine limits about its critical grid potential so as to ensure accurate timing of the outgoing pulses. The arrangement is described in association with the system of Fig. 1. wherein the ranging is given by indications on cathode-ray tube 1 provided with a fluorescent screen 2 and a scale 3 calibrated in units of distance. For generating a rotating field for the tube and synchronously controlling the periodic transmission of signal impulses, an oscillator 9 and amplifier 10 provide an alternating current having a frequency equal to the desired rate of emission of successive pulses. This current is applied through a transformer 12 to a sweep circuit 83. The sweep circuit comprises a condenser 15 and a resistance 16 connected in series and through contacts 51 and 50 of a four part three-position switch 55 in series with a deflecting coil 7. In parallel with this circuit is another similar circuit in series with another deflecting coil 8. The cathode beam is thus caused to rotate at the same frequency as that of the keying frequency oscillator 9. The beam may, however, be caused to rotate at twice or four times the oscillator frequency in order to increase the accuracy with which indication of distance may be read. In the second position of the switch 55 part of the energy of the oscillator 9 is fed by means of line 65 and switch contacts 92 and 90 to a frequency multiplier 68. The doubled frequency is then fed through a sweep circuit 84 by means of the switch to the de. flecting'coils 7 and 8 causing the beam to rotate at twice the oscillation frequency. Energy of the keying frequency is also applied to a diode rectifier 95 through a phase adjusting circuit. A conductor 99 leads from the anode of the tube through a resistance 54 to the grid 5 of the cathode-ray tube causing the grid to be energized with a negative potential produced by the passage of the negative half cycles of the keying frequency through the diode 95, and therefore causing the cathode beam to be completely suppressed' during every alternate revolution in order to suppress unwanted signals picked up from the antenna 86 during these alternate revolutions. Signals picked up during the positive half-cycles of the keying frequency, however, give an indication on the cathode-ray tube, these signals including those transmitted and reflected back to the receiver. In the third position of the switch energy from the frequency multiplier 68 is fed by means of a conductor 115 and switch contacts 103 and 100 to a second frequency multiplier 81. The output from this is fed through a sweep circuit 85 by means of the switch to the deflecting coils 7, 8 causing the beam to rotate at four times the oscillator frequency. A diode 107 is connected in the same manner as the diode 95. When the switch is in this third position both diodes 95 and 107 are operative and the cathode beam is suppressed during the second, third and fourth revolution of every four. For the synchronous production of a highfrequency varying impulse, a portion of the current produced by the keying frequency oscillator 9 is fed to a transformer 20 for the control of the keying or impulse transmitting circuit. This includes an oscillator tube 22 which may be an oscillator of the velocity modulation type (Fig. 7, not shown). The impulse-producing circuit comprises a gaseous discharge tube 37. The anode of the tube 37 is connected through a resistance 41 to the positive terminal of a D.C. source 42 and also through a condenser 43 and a variable resistance 44 to the cathode 38. The condenser 43 is charged whilst the tube 37 is non-conducting, and discharges through the resistance 44 when the valve becomes conductive. The voltage of the secondary 21 of the transformer 20 is impressed across the resistance 46 through a phase-shifting circuit which comprises a condenser 45 and a variable resistance 47. The voltage drop across resistor 44 due to the condenser discharge through the tube is impressed on the grid 33 of the high-frequency oscillator 22 through the cathode ground connections and blocking condenser 89 and a highfrequency choke 49. In operation the keying frequency produced by the oscillator 9 is impressed upon the grid 39 of the tube 37 and upon the cathode-ray tube coils with such relative phase that the particular instant of emission of the signal impulse with regard to the instantaneous position of the cathode beam can be controlled. The grid 39 of tube 37 7 when driven positive due to the keying frequency allows the condenser 43 to discharge through the resistance 44, the voltage drop across which is applied to the grid 33 of the oscillator valve 22 causing it to overcome its initial bias due to a battery 35 and to oscillate until the condenser 43 has discharged sufficiently for the initial bias to cut the valve off again. In a modification (Fig. 8 not shown), a triode tube replaces the resistor 41. The grid of the tube is connected to a further secondary of the transformer 20 in phase opposition to the secondary .21. The grid of the triode will then be positive whilst the triode acts as a low impedance and the condenser 43 may be quickly charged. When, however, the grid of tube 37 becomes positive, causing it to conduct the grid of the triode becomes negative and it acts as a high impedance. A larger condenser 43 may be used with the circuit. The triode may also be used on the negative side of the D.C. line (Fig. 9, not shown).