Patent GB-605053-A (GB)
Title: Improvements in or relating to wireless signalling systems
IPC: G01S1/68
Filed: 1945-05-24
Abstract: 605,053. Radio navigation. WILLIAMS, F. C. May 24, 1945, No. 13064. [Class 40 (vii)] In a radio navigation system bearing information relative to a beacon transmitter is given on a mobile craft by the comparison of the phase of a first alternating current derived from the reception of pulse signals radiated repeatedly in cyclic order from each of a plurality of aerials spaced around the beacon transmitter with that of a reference alternating current whose frequency is that of the cyclic repetition of transmission from the spaced. aerials and whose phase is related to the cyclic order timing. At the beacon (Fig. 1) is provided a transmitter T connected over rotary switch S to one of four spaced aerials A, B, C, D. The pulse recurrence rate may be 5 kc/s. and switch S may rotate 50 times a second. A second transmitter To modulated at the same pulse recurrence rate but working on a different frequency feeds centre aerial O and is pulse width modulated in synchronism .with the rotation of switch S ; maximum pulse width is preferably sent at the same instant as the middle pulse of the group sent by North aerial A. At the craft, the spaced aerial signals are received by receiver 10 and the leading edge of each pulse used to trigger 1 microsecond pulse generator 15. Similarly, pulses from aerial O are received by receiver 12 and trigger I microsecond pulse generator 18. By phase adjustment it is arranged that the reference pulse 30; (Fig. 3b) leads the pulse from one of the spaced aerials by half a microsecond so that if each aerial A, B, C, D is spaced a distance " a " from O at the corners of a square as shown, then with a craft at P, a large distance away, the pulses 32 received. from A will be a/c cos # before the mid-point of reference pulse 30 similarly pulses from B will lead by a/c sin #, from C lag by a/c cos #, and from D lag by a/c/ sin #; "c" is the propagation velocity and # the angle shown in Fig. 1. By making " a about 250 ft., it is arranged that the variation in pulse alignment is never more than a quarter of microsecond and so the leading edges of the pulses from all the spaced aerials all come within the corresponding reference pulses. In the bearing waveform unit 16, an alternating current bearing waveform (Fig. 4a, not shown), dependant on the amplitude and sign of the deviation of the front edge of the bearing pulse from the centre of the reference pulse at any instant is derived. The fundamental frequency of this is compared in phase comparison unit 19 with the reference frequency obtained in unit 20 from the width modulation of transmitter To. The phase difference which is the angle # is shown on centre zero meter 22 and on scale 27 by means of pointer 28. Scale 27 is rotated by mechanical means in synchronism with phase-adjusting goniometer 21. Scale and meter are preferably calibrated in terms of'the bearing of the beacon from the receiver. An alternative embodiment (Figs. 5 and 6, not shown) avoids the use of two channels by having a switching arrangement whereby pulses generated are fed to one of the spaced aerials and, delayed and then width modulated as before, to the centre aerial. At the craft a similar switching arrangement, arranged to changeover for a given time after the receipt of a pulse, sorts the " bearing " and "reference" pulses into separate channels to be used as described. Delay lines are introduced to obtain the necessary overlap conditions between related ones of the two sets of pulses. The modulation of transmitter To can be of any waveform from which the fundamental can be derived on the craft. It is stated that it may be possible to provide the reference waveform from a stable oscillator carried on the craft. Again, the pulses from transmitter T may be width modulated to provide the reference waveform, reference pulses for the bearing waveform unit being provided by a phase-stable oscillator synchronized by the received pulses. Any number of symmetrically spaced aerials from three upwards may be used. Transmitters T or To can be used for width modulation speech transmission, the beacon operating frequencies being filtered out on the craft. In a simplified modification (Fig. 7), which defines a course line only, two aerials A<1> and B<1> are fed in turn through paths of equal length and the output from the bearing unit 16 (Fig. 2) which compares the pulses received from these aerials with those radiated from reference aerial O<1> is zero along the line X and of opposite phase, either + #/2 or - #/2 on opposite sides of that path. The goniometer 21 is not required for such a system. If the delay time to one of the aerials B<1> is increased, the course line which will be followed by maintaining the meter on the craft reading zero is a hyperbola such as is shown at Y.