Patent GB-620487-A (GB)
Title: Improvements in or relating to radio navigation systems
IPC: G01S1/24
Filed: 1946-02-06
Abstract: 620,487. Automatic control systems. O'BRIEN, W. J., and DECCA RECORD CO., Ltd. Feb. 6, 1946, No. 3723. [Class 38 (iv)] [Also in Group XL (c)] A radio navigation system comprises means for successively radiating from one of a pair of spaced antennµ short pulses of radio frequency energy at a given fixed pulse repetition rate and means for radiating from the other of the antennµ short pulses of radio frequency energy at a pulse repetition rate different from, but harmonically related to, said given fixed rate together with means for maintaining a fixed multiple-phase relation between the pulse repetition rates; on a vehicle to be navigated, receiving means for the signals of different pulse repetition rates are provided and a pair of alternating potential output signals obtained therefrom, the phase relation between which is indicated on a meter. The meter indication provides information as to the position of the craft relative to the equi-phase displacement contours which are created by the modulations of the transmitted signals. The system is intended for use with high-frequency signals to provide accurate indications at short ranges. In an embodiment one of the transmitters A is a master station whose pulse output is timed by an oscillator 6 of, for example, 300 cycles/sec. frequency. At the second or slave transmitter B radiation from the master station is received on antenna 7 and the pulses of 300 cycles/sec. are obtained by detection, filtered and fed to frequency-divider 10 whose output is a sine wave of 100 cycles/sec. This output is fed to multiplier 11 whose 400 cycles/sec. output is passed through phase adjuster 13 to pulse generator 14 modulating high-frequency transmitter 15. The output from antenna 2 is partly picked up by loop 16 and this is detected and applied to phase discriminator 19, also fed from the output of frequency multiplier 11 ; any difference in phase between the two discriminator inputs produces a control voltage output at 21 which is applied to phase adjuster 13 to counteract such phase difference and maintain the phase relationship between the modulations of the two transmissions constant. At the vehicle signals from both transmitters are received at 23 and passed through a common detector 24. Filter 26 passes only the 300 cycles/sec. signals from station A and filter 28 only the 400 cycles/sec. signals from station B. The outputs of these frequencies are brought to a common frequency of 1200 cycles/see. by multipliers 29 and 30 and compared in discriminator 31 supplying a continuous reading phase-meter 32. Further stages of frequency multiplication 37, 38, and 39, 40, provide finer indications of phase difference on meters 33 and 34 driven by discriminators 35 and 36. By utilizing a further spaced station working with another simply related pulse recurrence frequency a position fix may be obtained. This requires a further modulation channel in the receiver and another set of phase indicators. Specifications 620,479; 620,480, 620,507, [both in Group XXXVI], 628,125, [Group XL (c)], and 628,747 are referred to.