Patent GB-620479-A (GB)
Title: Improvements in or relating to radio navigation systems
IPC: G01S1/30
Filed: 1945-08-23
Abstract: 620,479. Automatic control systems for radio-navigation. O'BRIEN, W. J. Aug. 23, 1945, No. 21664. [Class 38 (iv)] [Also in Group XL (c)] A radio navigation system comprises spaced transmitters radiating signals of different but harmonically. related radio frequencies and means for maintaining a fixed multiple-phase relation among said signals so as to produce intersecting patterns of equiphase difference contours and, on a vehicle, means for simultaneously receiving said signals and means for separately indicating two independent multiplephase relationships existing among said received signals whereby the geographical location of the vehicle is defined. The phase difference of the signals from a pair of transmitters may be measured at a frequency which is the lowest common multiple of the individual frequencies, the individual signals being multiplied to the comparison frequency in separate channels of the receiver. In a system using three transmitters (Fig. 1), A, B and C, radiating synchronized signals of 60, 80 and 90 kc. per sec. frequency, the pair AB define equiphase difference contours 3 and the pair AC contours 4. The line joining AC is at an angle to that joining AB to give a satisfactory area of intersection of the contours. If the lines shown are regarded as lines of a given multiple of 360 degrees phase difference it is clear that any number of lines representing subdivisions of a complete electrical rotation may be inserted between them and moreover that the whole of such contours may be calculated and marked on a map from which a craft 5 knowing the phase relationships between the two pairs of signals may determine its position. It is preferred to divide a 360 degrees unit of phase difference into a hundred parts and to use direct reading decimal system phase difference indicators giving the cumulative total of all changes resulting from the motion of the vehicle so that if they are set correctly at a known position they will continuously show the vehicle's location. The three transmitters A, B and C, may be constructed as shown in Fig. 5, wherein A is the master station radiating signals of 60 kc. generated by stable oscillator 20. Slave transmitter C receives the signals radiated from A on antenna 22 feeding amplifier and divider 23 which passes a 30 kc. signal through phase controller 24 to amplifier 25 and frequency trebler 27 which energizes antenna C radiating a 90 kc. signal. A small loop 28 picks up the 90 kc. signal and applies it through phase shifter 30 to frequency doubler 31 whose 180 kc. output is applied to one input channel of phase discriminator 32; the other input of the discriminator is fed by frequency trebler 33 connected to antenna 22. The output of the discriminator 32, which is dependent on the phase difference of the inputs is applied to phase controller 24 to maintain the phase relation between the 60 kc. input and the 90 kc. radiated output of the slave station at a fixed and constant value determined by phase shifter 30. Slave transmitter B is similar to transmitter C . except that signals of 80 kc. are radiated and the phase comparison in the control system is made at 240 kc. If desired the intersecting contours may be created by two pairs of transmitters A, B and C, D, Fig. 2 (not shown), D being a further synchronized transmitter which may, for example, radiate a signal of 120 kc. A receiver for the system of Fig. 1 consists of three tuned channels 38, 39 and 40 connected to a common antenna 5 (Fig. 6). The output of the 90 kc. channel is fed to doubler 44 feeding one input of 180 kc. phase discriminator 43. Similarly, the output of the 80 kc. channel feeds one input of 240kc. phase discriminator 46 through frequency trebler 47. The 60 kc. channel feeds a frequency trebler 41 connected to the second input of discriminator 43 and also a frequency quadrupler 42 connected to the other input of discriminator 46. The outputs of the two discriminators are connected respectively to cumulative registering phase indicators 45 and 48, which show the position of the vessel with respect to the contour system. The indicators 45, 48 may have a needle, Fig. 7 (not shown), which completely rotates. round a main scale divided into a hundred parts for each 360 degrees of phase difference and three subsidiary scales over which separate pointers move indicating 10, 100 and 1000 revolutions of the main scale needle for one revolution over the subsidiary scale respectively. The receiver, phase discriminators and phase indicators are described in greater detail in Specifications 620,480, [Group XXXVI], 620,481,. [Group XL (c)], and 620,507, [Group XXXVI], respectively. Specification 584,727, [Group XXXVI], also is referred to.