Patent GB-663775-A (GB)
Title: Radio position determining system
IPC: G01S1/30
Filed: 1948-10-01
Abstract: 663,775. Radio-navigation. SEISMOGRAPH SERVICE CORPORATION. Oct. 1, 1948 [Oct. 9, 1947], No. 25697/48. Class 40 (vii). A continuous-wave, hyperbolic-contour, position-determining system comprises a pair of spaced transceiver units and a spaced transmitting unit, wherein continuously-radiated radio waves from the transceivers are alternately modulated to provide reference signals in accordance with the intermittent transmission of differing signals from the transmitting unit, two position defining indications being alternately obtained at a receiver by comparison of a position indicating signal, derived from the unmodulated transceiver and the intermittent transmission, with the reference signal. The transceiver units 10 and 12 may radiate, for example, 1700.30 kc. and 1602.125 kc. signals, respectively, and the transmitter 11 1601.875 kc. and 1699.70 kc. alternately under the control of motor 23 and commutator 22 which applies high-tension power to the valves of the transmitters 20 and 21 alternately, each for slightly less than half a cycle of rotation. When transmitter 20 is functioning signals from this station and from station 12 are received by 1602 kc. receiver 16 at station 10 and the 250 c/s. beat frequency is passed by filter 8 and used to modulate the transmission of this station to provide a reference signal. When transmitter 21 is functioning, on the other hand, its 1699.70 kc. transmission and the 1700.30 kc. transmission from station 10 as received by receiver 19 provide a 600 kc. beat frequency which is passed by filter 9 and used to modulate the station 12 transmission to provide a reference signal. The receiving unit. Position determination on a mobile craft is made by alternate determination of the phase relationship between the received signals providing the 250 c/s. and 600 c/s. beat frequencies respectively and the reference signals radiated at the same time. Two receivers 26 and 27 tuned to 1700 kc. and 1602 kc. are provided, the former feeding one input of phase meter 30 and also one input of phase meter 31 through 600 kc. filter 28 and the latter the other input of meter 30 through 250 c/s. filter 29 and the other input of meter 31. The phase-meters are preferably of the integrating type. When the transmitter 20 of station 11 is functioning receiver 27 receives signals from it and from station 12 to provide a 250 c/s. beat frequency fed through filter 29 to meter 30 which is also provided with the 250 c/s. reference signal transmitted to receiver 26 by station 10. Thus meter 30 shows the craft's position with respect to one contour system. When the transmitter 21 of station 11 s functioning, the signals from this transmitter and from station 10 provide a 600 c/s. beat frequency in the output of receiver 26 which is passed by filter 28 to phase-meter 31 where it is compared with the reference signal radiated by station 12 and received by receiver 27 so defining the craft's position with respect to a second (intersecting) contour system. In a second embodiment, Fig. 2 (not shown), filters 8, 9, 28 and 29 are replaced by relays actuated in accordance with the presence of the correct signal frequency in the output of the receiver with which they are associated to connect that receiver to the next unit and releasing when the required frequency is no longer present. It is explained that the four transmitters and their sidebands may be contained in a bandwidth of less than 10 kc., for example the following frequencies are suggested: Specification 452,235 is referred to.