GB1003317A - Radio navigational system - Google Patents

Abstract

1,003,317. Omni range navigation systems. STANDARD TELEPHONES & CABLES Ltd. July 27, 1962 [July 28, 1961], No. 27510/61. Heading H4D. In a commuted aerial or rotating aerial Doppler type V.O.R. system wherein the reference carrier wave is modulated with a first signal and the bearing signal derived from the phase - modulated signal received from the commuted aerials is compared at the receiver with the said first signal, the reference carrier wave is further modulated with a harmonic of the first signal, and a harmonic of the bearing signal derived by means of a phase discriminator is compared at the receiver with the said harmonic of the first signal. Such an arrangement provides an ambiguous fine bearing value from the said harmonic comparison in addition to the normal unambiguous course bearing value. In the arrangement of Fig. 4 an R/F signal from generator 37 is shifted through 9960 c/s. by an oscillator 41 and a single side-band modulator 40, and the resulting signal is fed via wire 42 to a capacitive rotor plate 44, which is rotated at 30 c/s. by a motor 35 and which feeds the signal to the 36 aerial in succession. The R/F signal from generator 37 is also amplitude modulated in modulator 38 with a 30 c/s. signal from a generator 36 coupled in synchronism with the motor 35 and is fed, as a reference signal, to the central fixed aerial 32. Harmonics of the signal from generator 36 are produced by harmonic generator 46 and the 9th or 270 c/s. harmonic is selected by filter 47 and fed to the modulator 38 to further amplitude modulate the reference signal. The arrangement of Fig. 5 is similar except that the balanced earthed loads 66 are substituted for alternate aerials and the aerials are fed with upper and lower side-bands (F+9960) c/s. and (F - 9960) c/s. through plates 64 and 67 respectively, the two plates being diametrically opposite and only one plate coupling to an aerial at a time. This arrangement results in a larger Doppler shift than in the arrangement of Fig. 4. A receiver, Figs. 2, 3, compatible with standard V.O.R. systems, comprises a second A.M. detector 10 feeding a L/F output circuit 11, the output of which comprises a 30 c/s. reference signal, a 270 c/s. reference signal, and a phasemodulated 9960 c/s. bearing signal, the maximum frequency deviation being Π480 c/s. at zero elevation at a repetition rate of 30 c/s. This 30 c/s. phase modulation repetition rate signal is detected in F.M. discriminator 17 and compared in phase with the 30 c/s. reference signal from filter 13, to give a rough unambiguous bearing value. The 9960 c/s. signal is also fed to a phase discriminator 14 which yields, together with filter 15, a 270 c/s. phase-locked signal for comparison with the 270 c/s. reference signal from filter 16, to give a fine ambiguous bearing value. Alternatively the outputs of discriminators 14 and 17 may be combined to give bearing information as described in Specification 694,549. The phase discriminator 14 is a harmonic phase discriminator working on principles given in Specification 695,085. It essentially comprises a phase discriminator 26 having the phase modulated 9960 c/s. signal at one input 27 and the said signal delayed in 25 to be in phase quadrature, at the other input 28. Such an arrangement gives a 270 c/s. output signal at 29. Harmonics other than the 9th may be less advantageously used, the omission of the delay network 25 giving even harmonics. The invention is said to be applicable to true Doppler systems comprising a bodily rotating aerial. The 270 c/s. reference signal may be transmitted on a separate carrier or on a sideband of the first carrier. Specification 899,951 also is referred to.