Patent GB-725817-A (GB)
Title: Antenna system and wave-signal transmitting system
IPC: G01S1/02
Filed: 1953-02-06
Abstract: 725,817. Radio navigation. HAZELTINE CORPORATION. Feb. 6, 1953 [Feb. 9, 1952], No. 3431/53. Class 40 (7) A radio beacon or radio direction-finding system operates by radiating from or receiving on two aerials systems two signals the point of translation of one of which is movable cyclically in a non-linear path. In a beacon system signals from a radio-frequency oscillator 10 are fed through frequency multiplier 11 to the aerial 12 which is shown as being physically rotated by motor 25 at the end of radial arms 12a. The output of oscillator 10 is also modulated by the output of audio oscillator 14 in balanced modulator 15 and fed to mixer circuit 19. The other input to mixer circuit 19 is from balanced modulator 16 feed from the same two sources through 90 degree phase shifters 17 and 18. Mixer 19 gives an output signal which is multiplied at 20 by the same factor used at 11 to give a reference signal fed to stationary aerial system 21. This signal is less in frequency than that supplied to antenna 12 by a constant audio frequency and it is momentarily interrupted when aerial 12 passes through a predetermined position by cam switch 26, 27. The beacon thus radiates a reference signal from aerial 21 interrupted once per revolution and a signal from aerial 12 which due to the Doppler effect appears in a given direction to vary cyclically in angular velocity, the phase of the cyclic variation being dependent on the direction considered. In the receiver for the beacon of Fig. 1 the signals from the beacon are received on aerial 30 and fed through the receiving channel units 31, 32, 33, to amplitude detector 34 wherein a difference frequency signal is derived whose frequency varies sinusoidally in accordance with the movement of aerial 12. This signal is applied to frequency detector 35 to give an aerial rotation frequency output which is passed by low-pass filter 36 to phase splitter 37 feeding the stator coils 38 and 39 of Selsyn 58. The rotor 40 of this Selsyn is manually rotatable by control 55 and feeds phase comparison circuit 41 having an indicator 49. The second input to comparison circuit 41 is derived from the receiver and detector units by high-pass filter 50 whose output is a differentiated pulse corresponding in time to the interruption of the transmission from the aerial 12. Short pulses of predetermined polarity only are passed by clipper 59 and shock exciter ringing circuit 51 to produce a reference-phase signal fed to unit 41. In determining the bearing of the receiver from the beacon, control 55 is adjusted until zero phase difference is shown by meter 49 and the bearing angle read off on scale 57. There is a 180-degree ambiguity in the indication which may be resolved by reference to the indicator 54 of phase-comparison circuit 53 fed from rotor 40 through a 90-degree phase-shifting network 52 and from reference generator 51. A direction-finding receiver operating on the same general principles is described with reference to Fig. 3 (not shown). In this, signals received by an aerial following a circular path are combined with signals received by a fixed aerial to give an aerial rotation frequency signal which is compared in phase with the output of a sinusoidal generator rotated in synchronism with the rotating aerial. Specification 594,530 is referred to.