Patent GB-626333-A (GB)
Title: Improvements in or relating to navigation aiding radio systems
IPC: G01S13/75
Filed: 1946-10-25
Abstract: 626,333. Radio navigation. SADIR-CARPENTIER. Oct. 25, 1946, No. 31792. Convention date, July 28, 1942. [Class 40 (vii)] The route to be followed by a mobile craft is marked out by a number of reflectors, identifiable by being comprised of elements of different numbers and/or spacing, of electromagnetic waves at known positions on the course. The craft is provided with a pulse transmitter and a receiver which receives the transmitted pulse energy which is reflected. This arrives back at the craft at a short time after the transmission dependent on the distance of the craft from the nearest reflector. This distance may be determined by the use of a type A cathode-ray tube display on the craft, a graduated scale being marked on the oscillograph. The heading of the craft relative to the direction of the reflector from the craft may be determined by making the transmitting antenna directive and rotary, the variation in amplitude of the deflection of the trace produced by the reflected signal showing how accurately the antenna is directed towards the reflector. The distance from, and orientation with respect to, the beacon may be combined with a compass indication to determine the geographical direction from the reflector and continuous knowledge of these factors on an aircraft enables the wind speed and direction to be calculated if the airspeed is known. The reflectors should be spaced so that at least one always provides adequate signal strength in the craft receiver ; if two reflectors do so the distances from them determined by the receiver may be used to find the position of the craft. Both the receiver and transmitter may be associated with directive antenna for greater accuracy in determining the craft direction. The reflecting devices may comprise tuned dipoles, a number being spaced apart distances of the order of decametres so that the number and spacing of the dipoles is a characteristic of a particular reflector and can be used for identification purposes as a corresponding number of similarly spaced echo deflections will appear on the oscillograph. Double width deflections may be produced by having the dipoles of the reflector sufficiently close for the individual echo signals to coalesce. To define an approach path 15 two series of reflectors 16<1>, 162 and 17<1>, 17<2> may be placed equally either side of it and the craft be provided with two stationary transmitting aerials 7<1> and 7<2> and two receiving aerials 8<1> and 8<2>, having their directional axes arranged to form a V symmetrically about the craft heading line. The transmitting aerials radiate pulses simultaneously and also trigger the oscillograph time base. Received echo signals from the two directive patterns are preferably applied to cause deflections of the trace in opposite directions. If the deflections caused for example by echoes from reflectors 16<1> and 17<1> are at equal distances along the trace the craft is on the approach course 15 and if the amplitude of the deflections is equal the heading of the craft is correct, Figs. 8-10 (not shown).