Patent GB-630080-A (GB)
Title: Improvements in or relating to radio navigation systems
IPC: G01S1/02
Filed: 1946-08-26
Abstract: 630,080. Radio navigation. O'BRIEN, W. J. Aug. 26, 1946, No. 25495. Convention date, Aug. 27, 1945. [Class 40 (vii)] In a radio-navigation system of the equi-phase difference type such as is described in Specification 620,479, the distance between successive zero phase difference contours at a given distance from the transmitters will differ with azimuth and in general the sensitivity of the system will differ with direction. To provide good sensitivity in all directions, two systems of transmitters are used, radiating equi-phase difference patterns which are angularly displaced so that each provides relatively high discrimination in sectors where the discrimination provided by the other is relatively low. An embodiment of the invention utilizes a pair of spaced radio-frequency transmitters with a central transmitter on the line joining the pair and another pair of radio-frequency transmitters disposed on opposite sides of the central transmitter on a line at right angles to the line joining the first pair, Fig. 1 (not shown). Signals of a given first frequency are radiated from the central transmitter and signals of the same two frequencies harmonically related to the first and having given multiple phase relationships therewith are radiated alternately from the transmitters of the two pairs. The central transmitter A (Fig. 2) may be a master transmitter 7, 9 radiating (for example) a 60 kc. signal which is modulated and unmodulated for equal periods of 1¢ seconds by audio oscillator 11 keyed by switch 12 camoperated by motor 13. The first pair of transmitters, slave stations B and C, receive the signals from station A and have frequency conversion means for deriving respectively signals of 80 kc. and 90 kc. and phase control apparatus for maintaining the multiple phase relation between the signals radiated. Each station also includes a detector for the 60 kc. received signal which during the period when the A station signal is modulated energizes relays 17 to connect the output amplifiers of the stations to their antennµ. During periods when the A transmission is unmodulated, relays 17 release and no signals are radiated by stations B and C. The second pair of transmitters B<1> and C<1> are of similar construction to stations B and C except that the relays operated from the detector circuits make, contact when unenergized and break contact when energized so that stations B<1> and C<1> radiate only during the periods when no signals are radiated from stations B and C. The receiver is similar to that described in Specification 620,481, having three channels for the separate signal frequencies and the two pairs of signals giving the position of the receiver on the intersecting co-ordinate system being compared in phase at a common multiple frequency for the pair. It differs, however, in that the outputs from the two phase discriminators 27 and 28 are applied either to a first pair of indicators 20 and 21 or a second pair 22 and 23, the first pair being connected when stations B and C are operating and the second pair when stations B<1> and C<1> are in operation. A detector 29 operating on the 60 kc. signal from the master station feeds the pulses of modulating signals to a circuit, Fig. 4 (not shown), similar to that described in Specification 642,368, which produces in output circuits 48 and 49 D.C. pulses respectively occurring within, and being slightly shorter than, the time of reception of the modulated 60 kc. signal from station A and similar pulses occurring wholly within the unmodulated 60 kc. reception period. Pulses in circuit 48 operate relay 24 so that indicators 20 and 21 are connected and show the position of the receiver in terms of the co-ordinate system created by the transmission from stations A, B and C. Similarly, pulses in circuit 49 connect indicators 22 and 23 which show the receiver position in terms of the A, B<1>, C<1> co-ordinate system. As the indicators have no restoring means and the operating cycle is short, the indications are both effectively continuous. Specification 620,480, [Group XXXVI], ,also is referred to.