Patent GB-883345-A (GB)
Title: Direction finding system with phase comparing and indicating system
IPC: G01S1/02
Filed: 1958-12-24
Abstract: 883,345. Phase measurement. STANDARD TELEPHONES & CABLES Ltd. (International Telephone & Telegraph Corporation). Dec. 24, 1958, No. 41705/58. Class 37. [Also in Group XL (c)] A phase indicating system comprises a source of reference signals regularly repeated at a predetermined frequency, a source of coarse phase - indicating signals regularly repeated at the predetermined frequency and having a phase which is variable relative to the phase of the reference signals, a source of fine phaseindicating signals regularly repeated at an integral multiple of the predetermined frequency and having a relative phase coherent  with the relative phase of the coarse signals, means jointly controlled by the coarse and fine signals for rotating an indicating shaft at a speed corresponding to the predetermined frequency so that the instantaneous orientation of the shaft represents the instantaneous phase of the coarse phase indicating sigrals with a degree of accuracy determined by the instantaneous phase of the fine phase indicating signals, and means controlled by the reference signals to give a continual indication of the phase of the coarse phase indicating signals relatively to the phase of the reference signals with the said degree of accuracy. In a navigation radio beacon of the Tacan type a pulse generator 10, Fig. 1, energizes a coder 11 at 2700 p.p.s. to produce pairs of 12Ás spaced pulses at similar frequency which key an RF oscillator 12 to energize rotary antenna 2 having a directional pattern, Fig. 4 (not shown), comprising a single major lobe and eight minor lobes spaced at 40 degree intervals therefrom. The antenna pattern rotates at 15 c.p.s. and a timer 19 synchronous therewith operates pulse generators 17, 18 to respectively emit to the pulse coder a group of 12 pulses spaced 30 Ás when the major lobe passes a given reference direction (e.g. north) and a group of 6 pulses spaced 24 Ás when each minor lobe passes the reference direction; the coder producing corresponding pairs of pulses to key the RF oscillator. The resultant signal, Fig. 5, composed of pulses 9 is amplitude modulated with a maximum peak 14a corresponding to the major lobes followed by other peaks 14b corresponding to the minor lobes, on which are superimposed the pulse groups 15, 16 corresponding to the passage of the major and minor lobes through the reference direction, and this signal is received by an omnidirectional antenna 22 of a craft, and demodulated to amplitude modulated pulse signals comprising a 15 c.p.s. component, a 135 c.p.s. component and a main reference signal component which are fed to a coincidence decoder 27; from the output of which the 15 c.p.s. and 135 c.p.s. components are filtered and which is limited and applied to a reference signal ringing circuit 28 tuned to 33 kc/s. to respond only to the 30Ás spaced main reference signal pulses. The 15 c.p.s. component is amplified to drive a synchronous motor 33 to rotate shaft 35, which carries a disc, Fig. 2 (not shown), having 40 degree spaced limiting pins 36 on the face thereof engaging therebetween a radial arm 37 carried by a shaft 40 to rotate dial 42 in synchronism with the beacon antenna within an accuracy sector of 40 degrees, and the 135 c.p.s. component is amplified to excite an electromagnet 38 coupled to a .9-tooth magnetic wheel 39 mounted on shaft 40 to rotate the 40 degrees dial with an accuracy sector of , since 9 the phase of the 135 c.p.s. component varies 360 degrees for a 40 degrees phase variation of the 15 c.p.s. component corresponding to 40 degrees variation of bearing. The phase relationship between the 15 c.p.s. and 135 c.p.s. with respect to the main reference signal is determined by the bearing of the craft from the beacon antenna, and the dial has a radial slot 49, Fig. 3, illuminated by a circular neon tube 43 pulsed from trigger circuit 44 in coincidence with the arrival of successive reference signals at the ringing circuit 28, so that the position of the slot at illumination with reference to a surrounding calibrated circle 50 indicates the bearing of the craft from the rotary beacon antenna.