Patent GB-1483584-A (GB)
Title: Radio frequency pulse generators and pulse transmitters
IPC: G01S5/10
Filed: 1973-09-07
Abstract: 1483584 Transformers DECCA Ltd 2 Sept 1974 [7 Sept 1973 15 Nov 1973 (4 sheets) 25 Jan 1974] 42236/73 53062/73 and 03627/74 Heading HIT [Also in Division H3] A high power radio frequency generating arrangement for use in a Loran C navigational system comprises a torodial air-cured transformer, Fig. 18, the secondary winding 180 being connected in a tuned antenna circuit 181 while one or more primary windings 185, 186 are each divided into a plurality of separate winding segments, each segment together with an associated capacitor forming a respective oscillation-generating tank circuit. Pulsed oscillations of a common frequency are produced in parallel in the tank circuits by simultaneously charging the respective tank capacitors and then discharging them through the respective winding segments. These oscillations are simultaneously coupled into the antenna circuit. Two primary windings as shown may be used, the arrangement either imparting constructional symmetry or enabling by alternative energization the phase of successive trains of radio frequency to be reversed for station identification purposes. The transformer includes switchable damping windings 183 connected to damping resistors 189 and switches 190 for controlling the length of each generated pulse. Pulse, generation.-A single tank circuit 11, 12 is shown in Fig. 1, the tank capacitor 12 being charged from a D.C. source 10 through a low frequency resonant circuit formed by a capacitor 11 and a choke 16 when a thyristor 17 is triggered. An overload relay 21 restricts the charging current, while surge damping and smoothing is effected by a diode 27, choke 28 and resistor 29. When the capacitor 11 is charged the closures of a bidirectional switching device comprising a diode 13 and a thyristor 15 produce a tank oscillation, this being coupled through primary winding segment 12 and secondary winding 30 to a tuned antenna 31, 32. The generated pulse is terminated by thryistor switches 35, 38 which when closed connect windings 34, 36 coupled to the tank and antenna circuits, respectively, to damping resistors 33, 37. Alternative forms of suitable bidirectional thyristor switch arrangements are disclosed, Figs. 4 to 6 (not shown). As an alternative to coupled windings a series or parallel damping resistance may be included in the antenna or tank circuit when a thyristor switch is closed, the action of the switch being inverted by the use of T networks imparting a 90 degree delay or advance, Figs. 7 and 8 (not shown). A trigger circuit for controlling the operation of a thyristor switch is described, Fig. 15 (not shown), while Fig. 16 (not shown) features a schematic circuit for sequentially operating the tank, damping and charging triggers. Phase reversal of pulses. Two alternatively energized primary windings may be used, Fig. 20 (not shown), or an antenna coil 221, Fig. 21, may be energized via a coupling circuit 222 which comprises series-coupled coils 223, 224 respectively associated with opppositely sensed primary windings 225, 226. In Fig. 22 each tank circuit such as winding segment 233 and capacitor 236 has two alternative charging circuits 237, 238 of opposite polarity. According to the required phase of the pulse to be transmitted, one or other of the charging circuits is used and an appropriately poled thyristor 241 or 242 then triggered. The other thyristor is made conductive half a cycle later. Transformer construction.-The coil assembly may comprise a cylindrical former 310, Figs. 23 and 24, on which is wound a secondary winding of parallel connected Litz wires. The primary winding consists of 46 separate segments each extending around a portion of the annular region between the secondary winding and the inner surface of a closed cylindrical shield 312. The end connections of each winding segment extend in pairs through respective holes in the shield. An alternative construction employs a shield in the form of a hexagonal sleeve 318 with one closed end, Fig. 25. A cylindrical former 322 carries a secondary winding 323 and a plastics hexagonal former made up of six separate sections 324. One sixth of the primary winding segments are carried by each former in the manner shown for the wire loop 325, 329 in Fig. 27. A modification involves the use of arcuate formers, Fig. 32. A further constructional form involves overlaid primary and secondary windings on a toroidal former, Figs. 33 and 34 (not shown).