Patent GB-630877-A (GB)
Title: Improvements in or relating to means for identifying areas or lanes in a radio navigational system
IPC: G01S19/11
Filed: 1946-11-06
Abstract: 630,877. Radio navigation. DECCA RECORD CO., Ltd. Nov. 6, 1946, No. 33036. Convention date, June 3. [Class 40 (vii)] Transmitting apparatus for a hyperbolic radio navigation system comprises two pairs of stations, each radiating a radio frequency signal, the two pairs of signals being all of different frequencies, and means for maintaining a fixed multiple-phase relation between the signals of each pair. For the purpose of lane identification, means are also provided for stopping the radiation from one of said pairs of stations and for radiating from the other stations both pairs of signals while maintaining a fixed multiple phase relation between them. Preferably the signals are all harmonics of a basic frequency, for example in Fig. 1 one pair of stations A, B, may radiate 48 kc. and 72 kc. respectively, and the other pair C, D, 50 kc. and 75 kc. The two pairs of signals establish equi-phase contour systems 1 and 2 respectively. For the identification of one lane out of a number of lanes in each pattern, transmission from C and D is periodically stopped and 48 and 50 kc. signals are radiated from A and 72 and 75 kc. from B (providing identification of one lane in 24 in the AB pattern) then radiation from A and B is stopped and 50 and 48 kc. are radiated from C, and 75 and 72 kc. from B (identifying one lane in 25 of the CD pattern). After the lane identification transmissions, normal radiation is resumed. If A and C are the master stations in each pair, these stations may consist of a 1 kc. harmonic generator (Fig. 2, not shown) with frequency selective amplifiers for passing on to the aerial the 48 kc. and 50 kc. harmonics as required. At slave station B, Fig. 3, 48 kc. signals from master station A are received on loop 16 and passed through a frequency dividing and multiply chain to drive 72 kc. power amplifier 12 coupled to antenna 11. Included in the frequency changing chain is an electronic phase-adjuster controlled by a voltage from discriminator 26 dependent on variation in the multiple phase relation between the radiated 72 kc. signals picked up by loop 22 and received 48 kc. signals from loop 31 and serving to correct any such phase variation. During lane identification in the AB pattern station A radiates 48 kc. and 50 kc. signals and the 50 kc. signals, also received on loop 16, are frequencydivided at 64, fed through an electronic phaseadjuster 65, phase-reverser 66, and then multiplied to 75 kc. and radiated from antenna 11. To maintain the phase relationship the 75 and 72 kc. radiated signals are received on loop 22, are mixed and detected at 70, and the beat frequency multiplied to 6 kc. and applied to one input of discriminator 72. The other input to discriminator 72 is derived from the heat frequency of the 48 and 50 kc. signals picked up by loop 31, and the discriminator output is fed to phase-adjuster 65 to correct any variations in phase between the radiated signals. On first commencing lane identification transmission the frequency divider 64 may synchronize 180 degrees displaced from the required relationship, and in this case the discriminator output is sufficiently large to operate ratchet relay 81 controlling phasereverser 66 and thus introduce a compensating phase reversal. If it is desired to separate the station pairs AB, CD, by considerable distances, signals from these stations may be synchronized by making each member of the pair a slave to a master station between them. Such master stations are shown at X and Y (Fig. 1), and may radiate 24 kc. or 25 kc. (or during lane identification, both simultaneously). A master staton X and slave station A are described with reference to Figs. 5 and 6 (not shown), the principles by which the frequencies are obtained and held in desired multiple phase relationship being the same as in the previous example. The way in which the phase relationships of the signals are initially set to the desired values by manually-operated phase-adjusters is described and harmonic generators such as 81a (Fig. 3) are used to obtain check readings for testing if phase drift has occurred. Receiver. At the receiver signals are received by antenna 35 and separated by 72, 48, 50 and 75 kc. amplifiers 37, 38, 39, and 40, respectively. The normal AB pattern indication is shown on indicator 46 operated. by discriminator 43 determining the multiple phase relationship between the 72 and 48 kc. received signals. Similarly indicator 52 shows the normal CD pattern indication. For lane identification readings the 48 and 50 kc. signals are detected at 53 and the 2 kc. beat frequency multiplied by 3 and fed to discriminator 57. The other input of the discriminator is obtained by doubling the beat frequency of the jointly detected 72 and 75 kc. signals. and the discriminator output is fed to lane indicator 62. Specifications 620,479, 625,983 and 630,685 are referred to.