Patent GB-642399-A (GB)
Title: Improvements in or relating to radio navigation systems
IPC: G01S1/30
Filed: 1946-08-21
Abstract: 642,399. Radio navigation; valve relay circuits. O'BRIEN, W. J.' Aug. 21, 1946, No. 16635/49. Divided out of 642,368. [A Specification was laid open to inspection under Sect. 91 of the Acts, Feb. 28, 1947.] [Classes 40 (vi) and 40 (vii)] A radio navigation system comprises three spaced antennµ, one of which transmits a continuous radiation of a given frequency whilst the other two are each arranged to transmit two other frequencies, the three frequencies being harmonically related and having fixed multiple phase relationships, means being provided for operating the other two antennµ alternately. The continuously radiating antenna A (Fig. 2, not shown) may be energized at 60 kc. from the master transmitter and this signal may be modulated by a low-frequency and unmodulated for equal periods, each of about 1¢ seconds. At the slave stations B and C the 60 kc. signal is received and converted in frequency to 80 and 90 kc., the output signals being maintained in constant phase relation with the 60 kc. input. The received signals from A are also fed to detectors controlling relays in the aerial circuits so arranged that the aerial circuit at B is completed when modulation occurs and that at C is completed when no modulation occurs. In a suitable receiver for such a transmission system, the received signals are separated by tuned amplifiers 29, 30 and 31. The 60 and 90 kc. signals are multiplied respectively at 131 and 32 to frequencies which when mixed and detected at 33 give a 60 kc. beat for comparison with the output of the 60 kc. amplifier 31 by discriminator 34. The output of the discriminator 34 is fed to phase indicator 35 for the AB pattern and to indicator 36 for the AC pattern by means of relays 37 and 38 controlled by device 39 which includes a detector for the 60 kc. signals. The detected pulses of low-frequency modulation are fed to the relay control circuit (Fig. 4) through resistor-capacitor network 43, 44, 45, 46 which serves to convert the square applied waveform into a quasi-sinusoidal one. This, amplified by valve 40, is applied to relay 47 which operates when the current reaches a certain value and releases before the current becomes zero and is thus operated for a period of time within and shorter than the modulation period. Contacts 47b of the relay operate to apply a square waveform somewhat longer than the unmodulated period to a similar shaping circuit, amplifier and relay 56. Owing to the delay in closing of the relay and because it drops out before the end of the applied pulse this relay is closed for periods less than, and contained by, the unmodulated signal period. Contacts of relays 47 and 56 are connected in the energization circuits of relays 37 and 38 respectively and connect the appropriate phase indicators in circuit as soon as the system has stabilized after each change over. The indicators have no restoring spring and so effectively give a continuous reading. It is pointed out that the patterns of the AB and AC contours are similar and contain 12 lanes of 360 degrees phase change for each half wavelength separation of the stations at the basic frequency of 10 kc. (of which the radiated signals are harmonics). Specifications 620,479 and 642,400 are referred to.