Patent GB-604925-A (GB)
Title: Improvements in or relating to radio direction indicating systems
IPC: G01S1/02
Filed: 1945-04-20
Abstract: 604,925. Directive radio systems; radiolocation. STANDARD TELEPHONES & CABLES, Ltd. April 20, 1945, No. 10043. Convention date, April 26, 1944. [Class 40 (vii)] In direction-indicating arrangements involving the use of overlapping beams for transmission or reception, the different received energies are compared and only when they are substantially equal is energy released to operate an indicator. With an indicator of the cathoderay-tube type, this produces a sharper indication. Radiolocation system, Fig. 1. Pulses transmitted from an aerial 6 are received after reflection on aerials 8, 9 arranged to have overlapping response patterns. The three aerials are mounted on a common reflector 14 and the whole assembly is continuously rotated by a motor 15. The receiving aerials are connected to separate similar receivers 22, 23 and the detected output pulses 18, 19 are compared as to amplitude in a comparator 30 (shown in detail in Fig. 4) which releases energy to the control electrode 38 of the C.R.T. indicator to brighten the trace only when the amplitudes are substantially equal. The cathode beam is deflected circularly by coils 32 rotated by motor 15 and radially by a time-base 34 controlled by the pulse generator 1 so that a P.P.I.- type display is given. In a modification, Fig. 3 (not shown), a single receiver is used connected by an electronic switch alternately to aerials 8, 9 for one pulse-repetition period so that it responds to alternate pulses from each of the aerials and the detected pulses are separated by a second synchronous electronic switch and applied to the comparator after they have been brought into time-coincidence by a delay network in one path. Simple direction-finding. The system of Fig. 1 may be used solely as a direction-finder by omitting antenna 6, transmitter 4, pulse generator 1 and time-base generator 34, a fixed voltage being applied to coils 32 to give a radial deflection. In a modified system, one of the receivers 22, 23 may have a gain-control circuit calibrated to show direction when the gain has been varied to produce an output from the comparator. Beacon system, Figs. 5, 6. The transmitter, Fig. 5, comprises two aerials 78, 80 mounted on a reflector 82 and arranged to provide overlapping beams which are separately modulated from tone sources 74, 75. The aerial assembly is continuously rotated and a synchronizing signal is sent out from a further aerial 89 at a definite point in each revolution. In the receiver, Fig. 6, the detected tone frequencies are separated by filters 93, 94 and passed to the comparator 96. The synchronizing signal which is of relatively large amplitude is separated by a threshold-device 95 controlling a rotary timebase generator 1.00. Before reaching the comparator, the two different tone frequencies may be converted to a common beat frequency. Comparator, Fig. 4. A high-frequency oscillation from generator 54 is fed in opposite phase to the grids of two valves 61, 62 and the signals to be compared are fed over leads 28, 29. When the amplitudes of the signals are equal, there is no high-frequency voltage at point 67 so that rectifier 68 controlling a blocking circuit 71 has no output and the signal lead 29 is connected through lead 72 to the control electrode of the indicator.