Patent GB-840253-A (GB)
Title: Improvements in or relating to radio-controlled explosive mines
IPC: F41G7/00
Filed: 1958-05-15
Abstract: 840,253. Radar; radio receiving apparatus. SOC. DE FABRICATION D'INSTRUMENTS DE MESURE. May 15, 1968 [May 15, 1957], No. 15672/58. Classes 40 (5) and 40 (7). [Also in Group XXI] An explosive mine incorporates a continuouswave Doppler radar for exploding the mine in the presence of bodies moving at a low velocity. As illustrated in Fig. 3 and Figs. 1, 2 and 4 (not shown), the mine comprises a cylindricalhemispherical fragmentation metal casing 1 containing the charge 4 and detonator 10, lead ballast 3 to maintain the mine upright and screened compartments 6, 7, 8 containing the radio-frequency, low-frequency and power supply components of the radar. A quarter-wave aerial is fixed to a socket (Fig. 4, not shown) on the compartment 6 and comprises a silverplated copper tube 12 with a projecting slidable rod 13 which is adjusted to tune the aerial circuit and then soldered to the tube; the aerial may be protected by a polythene radome 2. As shown in Fig. 5, the radar comprises an R.F. triode oscillator 21 of frequency F (e.g. 300 Mc/s.) and an L.F. triode oscillator 27 of frequency f (e.g. 800 c/s.) which includes a transformer, Fig. 6 (not shown), having four windings 29, 30, 31 and 32, the anodes of valves 21 and 27 being connected respectively through the transformer coils 29 and 31 to opposite ends of a potentiometer 33 whose slider is connected to the H.T. supply 47 so that the triode 21 functions simultaneously as an amplitude-modulated transmitter and as a super-regenerative receiver of quench frequency f, an output of frequency f being obtained from the transformer winding 32, said output being amplitudemodulated at the Doppler frequency #F by objects moving within the radar field. The output from the winding 32 is applied through an amplifier 36, band-pass filter 38 and amplifier 37 to a detector 40 whose output is applied to one coil 41 of a differential relay 43 controlling a contact 46 in the firing circuit of the detonator 10. The amplitude of the output from the winding 32 also depends on stationary reflecting objects within the radar field and in operation the slider of potentiometer 33 is adjusted to produce an output of small amplitude in the absence of moving objects, the resulting current in the relay coil 41 being neutralized by a backing current in a coil 42 produced by a battery 44 and variable resistor 45. With such an arrangement any drop in output from the detector 40 due to failure of the H.T. power supply or the valves 21, 27, 36, 37 will cause the backing current in the relay coil 42 to operate the relay and detonate the mine, thus preventing recovery of a defective mine by hostile agents. Alternatively the D.C. component of the output from the detector 40 may be eliminated by a low-pass filter 58. When the mine has been set in position it is activated by operating a trip-switch 11 which (1) earths the cathode of valve 21, (2) connects in the H.T. supply 47 and (3) connects the battery 44 to the resistor 45 through the lower normally-closed contact of a two-position switch 49 to a motor 50 which rotates a cam disc 51. After a predetermined time interval the cam 51 closes a switch 53 to connect the battery 44 to the detonator switch 53 and connects the arm of the switch 49 to its upper contact, thereby stopping the motor. The mine may be de-activated from a remote point by connecting a battery between points 54 and 55, thereby energizing the motor 50 to rotate the cam 51 until the switch 53 is opened. In a modification, Fig. 7 (not shown), a single common triode is used for the R.F. and L.F. oscillators. Specification 584,726 is referred to.