Patent GB-626647-A (GB)
Title: Improvements in or relating to navigation aiding radio systems
IPC: G01S1/02
Filed: 1946-07-05
Abstract: 626,647. Radio navigation. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. July 5, 1946, No. 20214. Convention date, Nov. 29, 1941. [Class 40 (vii.)] A radio-navigation system comprises means for radiating pulses of radio energy from a plurality of predetermined locations in predetermined time relation, and a receiver therefor at the mobile craft together with an oscillator driving a timing indicator at a substantially constant rate and means for applying the received pulses to the indicator to denote their relative times of reception whereby the position of the craft may be determined. In an embodiment using three transmitters, A, B, and C, connected by synchronizing lines SL, the pulses are radiated at a carrier frequency of the order of 500 Mc/sec. and a pulse recurrence frequency of 33<1>/3 per second. At the craft the pulses are fed through receiver 1 to radial deflecting electrodes 5, 7, 9, of cathode-ray indicators 11 13 and 15. A stabilized 100 Kc/sec. oscillator 17 is connected to a frequency-divider 27, lowering the frequency to 10 Kc/sec., which frequency is fed to a further divider 35, the frequency of the output being 1 Kc/sec. Outputs from units 17, 27 and 35 are fed respectively to phase shifters 21, 29, 37, phase shifters 23, 31, 39, and deflecting plates 25, 33, and 41, of the indicators 11, 13 and 15, to produce traces rotating at the frequency of the inputs. The phase shifters 21, 29, 37 are used to set the first pulse indicated to the zeros of the scales 47, 49 and 51, so that the difference of the arrival times may be read off to a high degree of accuracy. The oscillator 17 is preferably synchronized with the incoming pulses by using a further frequency divider 43 to obtain a signal of the system pulse recurrence frequency from the oscillator, and this is applied with the incoming pulse signals to a balanced modulator 3 whose output is dependent on the relative phase of the applied signals and is used by automatic frequency control device 45 to effect the synchronization. The balanced modulator 3 may be affected by pulses arriving at different times from the various transmitters; if this is the case the frequency of the carrier of one of the stations is made slightly different from the others and although all the signals are passed by receiver 1 only the signals of the different' frequency are accepted by filter 53 and passed to modulator 3. It is stated not to be essential to distinguish between the pulses from the different locations as the craft may be navigated along a course, and by observing the movement of the pulses it is possible to determine if the area of location of the transmitters is being departed from or approached, alternatively direction-finding technique may be used to determine the bearing of one of the transmitters if its carrier is distinguishable. Continuous pulse identification may be arranged by using different carriers for each location and either separate receivers for each channel or a single receiver successively tuned to each channel. As the fastest indicator beam rotates a thousand times between corresponding pulses and the other indicator beams in proportion the deflections of the pulses will be difficult to observe. To avoid this the beams may be masked, either optically or electrically, except during one or two rotations containing the pulse deflections. In this connection attention is directed to Specification 626,654, claiming an electrical blanking arrangement.