Patent GB-687166-A (GB)
Title: Radio position determining systems
Inventor: HAWKINS JAMES EDWARD
IPC: G01S1/30
Filed: 1950-06-29
Abstract: 687,166. Radio navigation. SEISMOGRAPH SERVICE CORPORATION. June 29, 1950, No. 16323/50. Class 40 (vii). A position determining system comprises three spaced stations radiating radio waves to form two overlapping sets of hyperbolic position lines together with a receiving unit and is characterized by the provision at two of the stations of means for heterodyning the wave received from the other station with the wave produced by that particular station to give a reference signal transmitted to the receiving unit where each is compared with a similar signal derived directly from the same two waves to provide two position defining indications. In one embodiment the three transmitting units 10, 11 and 12 each transmit a different carrier wave modulated by a different audio frequency and the beat frequencies between the carrier signals and between the modulation signals from the pairs of stations 10, 11 and 11, 12 are compared in phase at the craft receiver with reference signals of similar frequencies derived at stations 10 and 12 and transmitted to the craft. Fig. 2 shows the stations 10 and 11 in blank detail; station 12 is similar in construction to station 10 except that the frequencies handled are different. Station 10 includes units 10a, 10b, 10c, serving to generate and transmit a 1800 kc. carrier modulated with 1.75 signal. Similar units at station 11 generate and transmit a 1804 kc. carrier modulated with 1.75 kc. signal. Similar units at station 11 generate and transmit a 1804 kc. carrier modulated at 1 kc. The carrier reference signal is derived by receiving both carriers at 18 and separating out the 4 kc. beat frequency by means of filter 19. The modulation reference signal is obtained by separating 1800 kc. and 1804 kc. signals by means of wave traps 20 and 22 and applying them to receivers 23 and 21. The audio-frequency output of these receivers is combined in mixer 24 and the 0.75 kc. beat frequency passed by filter 25 and applied along with the carrier reference wave from filter 19 to modulate the 1825 kc. reference signal transmitter 17. As indicated on the Figure, station 12 radiates an 1809 kc. carrier modulated by an audio frequency of 2.9 kc. and also a 1775 kc. carrier modulated with the 5 kc. carrier beat frequency reference signal and the 1.9 kc. modulation beat frequency reference signal for the pair of stations 11 and 12. At the receiver both 1800 and 1804 kc. signals are received by receiver 37 and the 4 kc. beat frequency separated by filter 36 and applied to one input of phase-meter 38. The other input of phasemeter 38 is fed with the 4 kc. reference signal separated by filter 34 from the output of 1825 kc. receiver 33. Units 26, 27, 28, 29, 30 and 31 operating in the same manner as units 22, 23, 24, 20, 21 and 25 at station 10 provide a 0.75 kc. modulation. beat frequency signal which is compared in phase with the 0.75 kc. reference frequency separated by filter 35 from the output of receiver 33 in phase-meter 32. Thus phase meters 32 and 38 provide coarse and fine position line indications with respect to hyperbolic contour systems having transmitters 10 and 11 as foci. A second receiving unit 13B feeding phase-meters 32a and 38a determines coarse and fine position line indications with respective contour systems having transmitters 11 and 12 as foci. For seismic work it is convenient to record the indications of the four phase-meters along with those of seismic wave detectors of which two, 50 and 51, are shown on a recording medium passed through recorder 40. To reduce the number of frequency channels used the reference signals obtained at station 10 from filters 19 and 25 may be used to frequencymodulate the 1800 kc. transmission, being recovered at the receiver by a separate phase modulation receiver, Figs. 2A and 3A (not shown). A further embodiment using highfrequency carrier frequencies modulated with signals of the order of 20 kc. is described with reference to Figs. 4 and 5 (not shown). In thissystem the coarse position determination is obtained by comparison of the differences between the signals of the order of 20 kc. (say of 0.2 kc.) and the fine position determination by comparison of the differences between the same signals after multiplication by a factor of a hundred. Specification 452,235 is referred to.