Patent GB-686389-A (GB)
Title: Radio location system
IPC: G01S1/30
Filed: 1949-11-05
Abstract: 686,389. Radio navigation. SEISMOGRAPH SERVICE CORPORATION. Nov. 5, 1949 [Nov. 27, 1948], No. 28383/49. Class 40 (vii). In a hyperbolic radio navigation system in which wave pulses are radiated from spaced points, means are provided at the mobile receiver for producing separate indications of the pulse transit time difference and the R.F. phase difference of the received signals. The invention is described as a means of resolving phase ambiguities in a beat-frequency phase system of the type disclosed in Specification 663,775, in which two intersecting families of donfocal equi-phase hyperbolic contours are produced sequentially by means of a master station 11 radiating alternately frequencies of 1700 kc/s. and 1900 kc/s. from transmitters 20, 21 and two spaced slave stations 10 and 12 radiating continuously frequencies of 1740 and 1960 kc/s., respectively, from transmitters 15 and 18. When transmitter 20 is operative, the signals radiated from transmitters 15 and 20 are received by receiver 27 on the mobile unit 13 and heterodyned to give a 40 kc/s. beat frequency which is applied through filter 29 and delay network 33a to a phase meter 30 where it is compared in phase with a reference 40 kc/s. signal produced by heterodyning the signals received from transmitters 15 and 20 at receiver 19 located at station 12, applying the resultant 40 kc/s. beat frequency through filter 19a and delay network 19b to modulate transmitter 18, receiving and demodulating the resultant modulated signal at receiver 26 on the mobile unit and applying the 40 kc/s. modulation signal to phase meter 30. Similarly when transmitter 21 is operative, the signals radiated from transmitters 18 and 21 are heterodyned at receiver 26 (mobile unit 13) and 16 (slave station 10) to produce 60 kc/s. beat frequencies and the beat frequency produced at station 10 is applied to modulate transmitter 15, the resultant modulated signal being received at receiver 27 (mobile unit 13) and the detected 60 kc/s. modulation signal being compared in phase with the 60 kc/s. beat frequency from receiver 26 in the meter 31. In accordance with the present invention, when transmitter 20 is operative the time interval TD between the leading edges of the pulsed 40 kc/s. wave trains P2 and P1, Fig. 3, from receivers 26 and 27, is measured by applying them in rapid alternation to the vertical deflecting members of the cathode-ray tube 35a by means of an electronic switch 36 which also shifts the vertical position of the beam in synchronism so that the two wave-trains are displayed as vertically displaced dotted waveforms but due to the high speed of switch 36, e.g. 1 Mc/s., the waveforms appear substantially continuous. The repetition rate of the sweep voltage applied to the horizontal deflection member of the cathode-ray tube is made equal to twice the switching rate of transmitters 20 and 21 so that substantially the whole of the pulses are displayed. When transmitter 21 is operative the time interval TD1 between the leading edges of the pulsed 60 kc/s. wave trains P3 and P4 is measured in a similar manner, the displayed waveforms P3 and P4 being displaced to the right of waveforms P1 and P2 by applying to the horizontal deflection coils 35b and 35c a square wave from oscillator 39 of recurrence frequency equal to the switching rate of transmitters 20 and 21. The loci of constant time differences TD and TD1 will be identical in shape with the equiphase contours and the locus of a particular time interval having stations 11 and 12 as foci may be adjusted to coincide with a particular equi-phase contour by adjusting the delay network 19b at station 12, an identical delay being provided by the delay network 33a in the mobile unit so that the positions of the equi-phase contours are independent of the above adjustments; delay networks 16b and 32a are provided at stations 10 and 13 for a similar purpose. Specification 452,235 also is referred to.