Patent GB-804060-A (GB)
Title: Improvements in or relating to navigation system
IPC: G01S1/02
Filed: 1949-12-28
Abstract: 804,060. Radar. GENERAL PRECISION LABORATORY, Inc. Dec. 28, 1949, No. 33166/49. Class 40 (7). In an aircraft navigation system, the drift angle and ground speed are obtained from the Dopplr change in frequency of radiations transmitted from the craft and reflected back from the ground. Indications of latitude, longitude and the estimated time and the course required to reach a given distination are given. In the system as shown in Fig. 6 the antenna 11 radiates waves which are reflected back from the earth to antennas 9, 13, 14 and from the received signals the Doppler frequency change is measured and the antennas are positioned by motor 27 so as to maintain the bisector of the angle between 13, 14 perpendicular to the true ground track. Motor 27 is energized by the resultant signal from the opposed outputs of band-pass filters 20, 25 which are tuned to the difference frequency fc between the local oscillator 12 and transmitter 11. Each filter is fed from a mixer 16 or 24, the input to which comprises the outputs from 12 and the respective antenna. The lobe patterns of 13, 14 overlap and the radiations received on each antenna along the path perpendicular to the true ground track having no Doppler shift, therefore are at the frequency of 11 and hence the mixers 16, 24 have outputs containing components at frequency fc which are transmitted by filters 20, 25. When the bisector between 13, 14 deviates from the position perpendicular to the true ground track the outputs from 20, 25 are unequal and motor 27 is driven to position 13, 14, and to correct the deviation. The antenna 9 is now aligned along the true ground track and the Doppler frequency change of the received signals is a measure of the ground speed. In a further embodiment, not shown, the B.P. filters 20, 25 are replaced by L.P. filters and the receiving antennas are automatically aligned so that the bisector of the angle between them lies along the craft ground track. In a third embodiment, Fig. 11, a selsyn arrangement is added to a Doppler ground speed and drift detecting system which gives direct indications of true ground track, latitude, longitude and the course which the craft must follow together with the time it will take to reach a given destination. As shown, the antennas 72, 73 are set automatically by motor 74 so as to lie on either side of the true ground track. In addition, the motor 74 and the compass 86 position the transmitters of the selsyns 84, 85 and the receiver 88 on shaft 91 is rotated through an angle proportional to the true angle of ground track. Shaft 91 simultaneously positions the potentiometers 66, 94 at which voltages are developed respectively proportional to the craft speed in the East-West and North-South directions and which operate the longitude and latitude indicators 114, 100 through the servo-mechanisms, 103, 104, 105, and 96, 97, 98. In order to correct the longitude indication for the latitude position, the ball-disc integrator 107 is introduced in the shaft 106 before the indicator 114. Also, the indicators 117, 123 are manually set to the longitude and latitude of the craft destination, the potentiometer tappings 132, 133 are moved by the differentials 120, 127, the voltages developed at the tappings are applied to the windings of resolver 138, the rotor of which is rotated to the null point by servo-system 142 and the resultant angular position of shaft 144 is proportional to the distance which must be covered in order to reach the required destination. The angle through which the craft must be turned to attain the desired course is indicated by the differential gearing 147. The time necessary for the craft to reach the given destination is derived by the division of the voltages representing the distance to be travelled and the speed of the craft which are developed at 149 and 65 respectively. The division is effected by the servo system 154, 155 and the potentiometer network 150, 151, 152, and is indicated on meter 159.