GB744619A - Improvements in radio receivers for cooperation with certain radio beacons to provide an indication of distance - Google Patents

Abstract

744,619. Radio navigation. SVENSKA AKTIEBOLAGET GASACCUMULATOR. March 18, 1953 [March 18, 1952], No. 7483/53. Class 40 (7). The invention comprises a receiver for a spiral phase field radio beacon the direction of rotation of the spiral phase of which is alternated between one hand and the other at a high rate. The receiver which may indicate both the range and bearing of the beacon has a rotating frame aerial and an omnidirectional aerial the outputs of both of which are amplified and fed after detection one to each of the field and moving coils of a moving coil instrument to give a range dependent indication. It is shown that for minimum reception the frame aerial will make an angle # with the perpendicular to the line joining the beacon and receiver where R being the range, # the wavelength and n half the number of poles in the beacon aerial system as explained in greater detail in Specification 694,721. If the frame aerial is rotated, then for one of the spiral phase fields the energy received as it rotates will vary as indicated by curve 15, and with a spiral phase field of the other hand there will be a displacement by 2# to the curve 16. Rapid alternation at the beacon between the two spiral fields therefore gives an output as shown by the continuous line of Fig. 2. The modulation waveform (Fig. 3) which can be extracted from the frame aerial output has a maximum at the aerial position corresponding to the minimum received signal intensity and in general its amplitude is 2A Cos (F.t) sin # where F is the angular velocity of the aerial, t time from a reference and A is a factor dependant on the aerial system constants and the incident signal strength. The factor cos (F.t) due to the rotation of the aerial is only a phasing factor and is not significant, taking the maximum of the signal, the amplitude is The value of A is determined from the signal amplitude received by the open aerial and when this is compared in the moving-coil instrument with the modulation waveform amplitude an indication is obtained which varies with R in accordance with the equation above. The instrument can be calibrated directly in range. The receiver may include a meter indicating the bearing of the transmitter from the receiver. For this purpose there is provided on the aerial rotation shaft a generator providing reference signals which are compared in phase with the output from the frame aerial in a cos-meter type bearing indicator. A block diagram (Fig. 5, not shown) of a receiver embodiment is given.