Patent GB-1094421-A (GB)
Title: Improvements in or relating to communications systems for synchronizing stations
Inventor: GRAHAM WALTON
IPC: G01S11/08
Filed: 1965-03-03
Abstract: 1,094,421. Radio navigation; automatic phase control systems. TRG Inc. March 3. 1965, No. 9068/65. Headings H3A and H4D. In a radio system for synchronizing first and second signals produced respectively at stations A and B, station B produces third signals, and station A has apparatus responsive to all the signals to control the occurrence of a first signal in a predetermined time relationship with respect to the production of a second signal at station B. The description relates to aircraft interrogating ground beacons, Fig. 1H as in the TACAN system to afford air-to-air ranging and direction finding for anti-collision purposes by non-radar means, and aircraft data reporting to the ground. In the simplest case, wherein the above predetermined time relationship is zero, interrogation and reference pulses 10ta 15tb, Fig. 1, are respectively transmitted from an aircraft and a beacon, the beacon reference and reply pulses 15ra, 20ra respectively are received at the aircraft and two sawtooth waveforms at the aircraft are started by pulse 10ta and respectively terminated by pulses 15ra, 20ra the second sawtooth charging circuit running at half the rate of the first; the difference between the respective terminal voltages E REF  and E RPY  is used as an error signal to make pulse 10ta simultaneous with pulse 15tb, Fig. 5 (not shown). One aircraft can thus determine the range of another by receiving its interrogation pulses; an interferometer affords the bearing of the other aircraft and a rangebearing display of other aircraft is afforded. The predetermined time between pulses 10ta, 10tb may be other than zero. If several aircraft are at the same range from the beacon it will fail to reply; therefore the aircraft interrogators transmit at one of n, e.g. 6, intervals in the pulse repetition period of the beacon reference pulses and on average at F, e.g. 22.5 pulses per second (p.p.s.), the beacon reference pulse repetition rate (p.r.r.) being nF. A random gate generator, Figs. 11, 12 (neither shown) utilizing a noise generator is interposed between the aircraft interrogation pulse generator 32, Fig. 4, and transmitter 36, the reference range memory circuit 48 being triggered by each pulse from generator 32.n may be further subdivided, e.g. n = 6 x 6, to increase traffic handling capacity, Figs. 7, 8, 9 (none shown). Height coding, Fig. 6.-It can be arranged that transmission of interrogation pulses is restricted to certain allowed positions to aircraft at particular altitudes, Fig. 6. In general each aircraft interrogates once every second to expressly provide altitude data to other aircraft and the beacon. Aircraft apparatus for transmission of height-coded pulses and receiving those from other aircraft is included, Figs. 10A, 10B (neither shown) in which a 810 p.p.s. (6 x 6 x 22.5) clock pulse generator is controlled in frequency and phase by a system similar to that above. The clock pulses also control the beginning of the sweep generator (114, Fig. 10A) for a plan-position indicator (118) displaying the range and bearing of other aircraft only if they are within the same altitude layer; the indicator may be of long persistence or a storage/display tube or replaced by digital indicators. An impending altitude change may be signalled. " Ghost " targets are inherently minimized; one arrangement utilizes " sweptgain ". General.-In the TACAN system the aircraft apparatus has " search " and " track " modes of operation; the synchronization described above takes place only during the track mode. A " pulse " may be a group of pulses, e.g. a pulse pair as in the TACAN system. Operation with several beacons within line-of-sight of the aircraft is described, including position-fixing by ranging on several beacons.