Patent GB-630314-A (GB)
Title: Improvements in radio guiding systems, especially for the blind landing of airplanes
IPC: G01S1/24
Filed: 1946-08-29
Abstract: 630,314. Radio navigation. FRANCE, H. G. DE, and RADIO-INDUSTRIE. Aug. 29, 1946, No. 25961. Convention date, April 27, 1940. [Class 40 (vii)] A radio navigation system comprises two spaced stations each transmitting a series of pulses, the reception of which at the receiver enables the bearing thereof with respect to an axis passing between the stations to be determined, and is characterized by at least one of the stations receiving and retransmitting the pulses transmitted by the other. Two transmitters (1) and (2) spaced apart a distance " d '' may be arranged so that pulses transmitted by (1) are received and retransmitted by (2), preferably on a different wavelength, or otherwise characterized, for example by differing in modulation envelope shape, so that they may be distinguished at the receiver. The receiver measures the time difference between corresponding pulses which, at a distance from the system, is a function of the bearing angle #. Measurement may be by means of a phasemeter, recording means, or preferably by means of a cathode-ray tube indicator. If a pulse A from station (1) triggers the time-base on which is displayed the pulse B from station (2), AB represents the time difference between the pulses. If now it is further arranged that station (2) radiates a pulse A<1> repeated by station (1) and producing an indication B<1> on the time-base triggered by A<1>, the distance BB<1> may be shown to be proportional to sin # and to provide a measurement of twice the accuracy of that provided by a system using synchronous transmission from stations (1) and (2). In a modification, a pulse from station (1) is received and retransmitted by station (2) which pulse is received and retransmitted by station (1) and so on. At the receiver pulses from transmitter (1) may alternately start scanning from " a " to " b " and from " b " to " a " (Fig. 4). If the corresponding pulses from transmitter (2) are A and B for two successive scans the distance AB is proportional to sin #; further, as A and B pulses appear on opposite sides of the line ab the sign of the angle # is also known. Distance determination, Fig. 5. If two transmitters (1) and (2) are used to guide an aircraft along a path XO to a landing ground Te, a third transmitter (3) may be placed as shown and preferably arranged so that pulses radiated therefrom are duly received and retransmitted by transmitter (1) whose pulses may then be repeated by transmitter (2). No indication of the craft's distance from the transmitters is given before the craft reaches the transmitter (3) but when it is between this and the line (1)-(2), the distance R may be determined from the measurement of the time difference between the arrival of corresponding pulses from transmitters (3) and (1), which is approximately equal to a constant less 2R/C, where C is the velocity of propagation. It is stated that the guide-line OX may be oblique to the line (1)-(2) if desired, and that the system in conjunction with an altimeter provides sufficient information to enable a pilot to make a blind landing on the airport.