GB959562A - Improvements in or relating to apparatus for warning aircraft of ground obstacles - Google Patents

Abstract

959,562. Pulse radar. LITTON SYSTEMS Inc. Aug. 15, 1960, No. 28258/60. Heading H4D. An electric circuit arrangement for use with an airborne radar comprises means for producing from a received radar signal having a " shadow " portion therein a signal indicative of the length of the shadow portion within a predetermined segment of the received radar signal corresponding to a limited extent of the terrain commencing at a pre-selected range from the radar. In the preferred embodiment, Fig. 5, the video output of the conventional airborne pulse radar, Fig. 9, A, includes echoes 122, 124, 126 from hills and minimum portions 128, 130, 132 corresponding in duration to the " hill shadows " slicer 86 produces from that signal a signal, Fig. 9, B, which appears as shown in Fig. 9C, at the output cf amplifier 92. A gate generator 146 comprises a phantastron circuit to provide a pulse 230, Fig. 9F, of switch-selectable duration which in turn provides a range gate pulse 234, Fig. 9I, from a generator 148 of further switch-selectable duration and commencing at the end of pulse 230; generator 148 is a similar phantastron circuit. The outputs of generator 146 and amplifier 92 are applied to a diode AND circuit 112, and of generator 148 and amplifier 92 to a diode AND circuit 110; circuit 112 output eventually provides for a " short range " alarm 312 and circuit 110 output from " long range " alarm 309. Long and short range alarms, Figs. 5 and 9. Shadow pulse 144, Fig. 9C, is integrated by a resistance-capacitance network 236 to produce a D.C. voltage, Fig. 9M, which is fed to a voltage comparator 252 comprising a D.C.- connected differential amplifier having its second input connected to a switch-selectable D.C. reference voltage 277. The D.C. voltage magnitude from integrator 236 depends on shadow duration and when it exceeds the selected reference voltage a relay 268 is actuated. Relay 288 actuation is similar, Fig. 9L (not shown). Circuits 290, 306 are inserted to maintain alarm lamps 309, 312 when the radar aerial is scanning. Arrangements are included whereby only echoes arising from a sector ahead of the aircraft are utilized for alarm purposes; these arrangements incorporate a relay 304. The output of transformer 318 is set to be zero when the radar aerial direction corresponds to the drift angle. P.P.I. display, Figs. 4 and 5. Additional data is presented on the conventional P.P.I. display; generators 352 and 370, Fig. 5, produce lines 71, Fig. 4, showing dangerous alternative courses and the cathode-ray tube beam is enhanced 74, Fig. 4, over the sector ahead of the aircraft. Circuits of the units of Fig. 5 which lie outside conventional radar 78 are described in detail with reference to Figs. 6 and 7 (neither shown). Specification 959,021 is referred to.