Patent GB-808917-A (GB)
Title: Long-range radio navigation system
IPC: G01S1/30
Filed: 1955-02-24
Abstract: 808,917. Radio navigation. LANGERAAR, W. Feb. 24, 1955 [Feb. 27,1954], No. 5619/55. Class 40 (7). In a long-range CW hyperbolic radio navigation system comprising a master station and a plurality, e.g. four, of spaced slave stations, the master station transmits frequencies (F1+70) and (F1 - 70) c/s and each slave station transmits frequencies (F2+70) and (F2-70) c/s where F1 and F2 are in the 14-10 kc/s band, the master station being operative during recurrent periods a, Fig. 1, and the slave stations being operative sequentially during each said period a. At a mobile receiver the 140 c/s beat signals derived from the master and slave signals are frequency multiplied by eight and compared in phase to indicate the corresponding hyperbolic co-ordinate. Means are also provided for automatically controlling the phase of the master and slave signals to reduce errors due to skywave propagation. The arrangement of the master and slave transmitters is shown in the right and left halves of Fig. 2; corresponding components at the two stations are identified by like references, the slave components being distinguished of a dark suffix. The frequencies (F170) produced at the master station by applying the outputs from an F1 c/s crystal oscillator 5 and a 70 c/s oscillator to a balanced modulator 6 are heterodyned in a receiver 10<1> at the slave station to give a harmonic of 70 c/s which is selected by filter 11<1> and applied through a phase shifter 12<1> to a frequency divider 13<1> whose 70 c/s output is applied together with the F2 c/s output from a crystal oscillator 5<1> to a balanced modulator 6<1> to give the slave transmission frequencies (F2 70). These frequencies are heterodyned in a receiver 10 at the master station and the resultant 140 c/s beat signal is applied through a phase shifter 12 to a discriminator 14 together with a 140 c/s beat signal obtained by heterodying in a receiver 10<11> the transmitted master frequencies (F170). The output from the discriminator 14 controls a switch 15 to select an output from an L.F. oscillator 17 or 18 according to the sense of the discriminator output and the selected output is applied to control servo motors 20 and 20<1> at the master and slave stations to maintain a predetermined phase relationship between the inputs to the phase discriminator 14 as indicated by a meter 22. As shown, one output from the switch 15 is applied directly to a servo motor 20 and another output is applied to the modulator 6; at the slave station the control signal at the output of the selected by filter 17<1> or 18<1> and applied through a control device 19<1> to the servomotor 20<1>. The servomotors 20 and 20<1> are energized in synchronism by 70 c/s inputs derived respectively from the 70 c/s oscillator 13 and the frequency divider 13<1> so that the phase correction is effected equally by the phase shifters 12 and 12<1>. The phase control signal transmitted from the master station may also be utilized at the mobile receiver to correct the indicated phase difference and the mobile receiver may be set up automatically by observing the phase difference between the beat signals transmitted from the master station and from a slave station located at the same site as the master station.