Patent GB-892095-A (GB)
Title: Improvements in or relating to navigation training apparatus
IPC: G09B9/26
Filed: 1958-03-24
Abstract: 892,095. Radio navigation trainers; automatic phase control systems. GENERAL PRECISION Inc. March 24, 1958 [March 22, 1957], No. 9444/58. Classes 40(5) and 40(7). Relates to means for simulating the fan marker beacons signals, the cone of silence and the Z marker signals in a known form of radio navigational training apparatus which simulates a four-course A-N overlapping-beam beacon. According to the present invention coded audio fan marker signals are applied to the pupils headset through a gate amplifier whose gain is inversely proportional to the amplitude of a D.C. control voltage which is a function of the distance R of the simulated aircraft position E, Fig. 4, from the position D of the simulated fan marker beacon, said control voltage being generated by (1) producing phase - displaced first and second A.C. signals proportional in amplitude to the components SE<SP>11</SP> and EE<SP>11</SP> of the distance ES of the aircraft E from the A-N beacon S resolved along and perpendicular to the associated A-N course line SB, (2) producing a marker-beacon-location A.C. signal of opposite phase to said first A.C. signal and of amplitude proportional to the distance DS of the marker beacon D from the A-N beacon S, and (3) combining said three A.C. signals and rectifying the resultant. The zone of silence of the A-N signals is simulated by applying the audio A-N signals to the pupils headset through a gate amplifier whose gain is proportional to a further D.C. control voltage which is a function of the distance ES of the aircraft E from the A-N beacon S, said further control signal being generated by producing phase-displaced third and fourth A.C. signals proportional in amplitude to the components of the distance ES resolved along and perpendicular to a selectable direction, combining said A.C. signals and rectifying the resultant; the Z marker signals are simulated by applying audio Z marker signals to the pupils headset through a gate amplifier whose gain is inversely proportional to said further control voltage. Means are also described for controlling the amplitude of the gated audio signals in accordance with the simulated altitude of the aircraft. The invention is described as combined with a known form of flight trainer comprising altitude, range and bearing servos 13, 12 and 11, Fig; 2, producing shaft rotations proportional to the altitude of the aircraft E and to its distance ES and bearing # from the A-N beacon S which are derived in known manner, Fig. 3 (not shown), from input shaft rotations proportional to the cartesian coordinates of the aircraft E from the beacon S. As shown in Fig. 2 the signals produced by an inner fan marker beacon located on the No. 1 course of a four-course A-N beacon, Fig. 1 (not shown), are simulated by applying the output from an A.C. source 200 to an amplifier U-201 through a potentiometer R-201 controlled by the altitude servo 13 and shaped to simulate the vertical characteristic of the marker beacon radiation pattern, one output from the amplifier U-201 being applied to a resolver L-1 through a linear potentiometer R-202 controlled by the range servo 12. The angular position of the resolver L-1 is set in accordance with the difference between the aircraft bearing # from the bearing servo 11 and the bearing of the A-N course line SB as set in by a control 202 to produce the first and second signals proportional to SE and EE<SP>11</SP>, Fig. 4, which are applied to a summing amplifier U-203 through 45 degrees phase advance and phase retardation networks respectively. The marker-beacon-location signal is produced by applying a further output from the amplifier U-201 to a linear potentiometer R-203 which is set manually in accordance with the distance DS, Fig. 4, said signal being applied to the summing amplifier through a 45 degrees phase advance network so that it is in phase opposition-with the first A.C, signal. Coded marker beacon audio signals generated in a keying circuit 15 are applied to the pupils headset through a gate amplifier V-201 in series with a mixing amplifier U-220 and the gain of the gate amplifier V-201 is controlled by the negative D.C. control voltage obtained by rectifying the resultant output from the summing amplifier U-203 at X-201 such that the marker signal is only heard when the distance R of the aircraft E from the marker beacon D is less than a predetermined value, the amplitude of the signal increasing as the distance R decreases. An effective elliptical marker coverage area as shown in Fig. 4 is obtained by adjusting the relative attenuation of the first and second signal outputs from the resolver L-1; in this case the phase difference between these two signals may be other than 90 degrees. The major axis of the ellipse may be inclined to the A-N course by adjusting the phase relationship between the first signal and the marker-beacon-location signal. The outputs from the resolver L-1 are also applied to a further summing amplifier U-204 which in conjunction with corresponding components R-204, X-202 and V-202 simulate the signal produced by an outer fan marker beacon located on the same A-N course line and the above apparatus is repeated to simulate inner and outer fan markers on the other A-N course lines.  The zone of silence and Z marker signal are simulated by applying audio A-N signals and Z-marker signals from the keyer 15 to the mixing amplifier U-220 through gateamplifiers V-212 and V-211 respectively and positive and negative further D.C. control voltages for said gate amplifiers are generated by applying the altitude-modified range voltage from the amplifier U-202 to a resolver L-2 whose two outputs are applied in phase quadrature to a summing amplifier U-211, the resultant output therefrom being applied to positive and negative rectifiers X-212 and X-211. Since the altitude characteristic of the A-N signals differs from that of the marker signals, an additional D.C. gain control voltage is applied to the gate amplifier V-212, said voltage being produced by a shaped potentiometer R-243 controlled by the altitude servo 13. The relative amplitude of the A and N signals is controlled by known means not described. Additional signals, e.g. for beacon identification, may also be applied to the mixing amplifier U-220 through resistors R-240 and R-241. Fig. 6 shows an arrangement comprising a single summing amplifier U-601, controlvoltage rectifier X-601 and gate amplifier V-601. The resolved outputs from all the fanmarker resolvers (L-1 only shown) and the Z-marker resolver L-2 are applied to corresponding fixed contacts on sections W and X of a 4-section selector switch, the outputs from the marker location potentiometers, R-203, R-204 &c., being applied to section Y and the different audio marker signals from the keyer 15 being applied to section Z. In this arrangement the A.C. output from the source 200 is applied directly to the potentiometers R-203, R-204 . . . and to all the resolvers, the outputs from the W and X sections of the selector switch being applied to the summing amplifier U-601 through linear potentiometers R-601, R-602 controlled by the range servo 12 and the output from the amplifier U-601 being applied to the rectifier X-601 through shaped altitude potentiometer R-604 or R-609 as selected by a relay K-601 in dependence on the presence or absence of a marker-location voltage from section Y of the selector switch, the latter condition obtaining during the Z-marker period. Pulses from a generator 16 are applied to the operating coil LS of the selector switch WXYZ through a gate valve V-602 controlled by the positive control voltage from the rectifier X-601 so that the switch steps cyclically until the control voltage falls below the level corresponding to the edge of a marker beacon coverage area thereby blocking the gate valve V-602 and stopping the switch until the aircraft emerges from the service area of the marker beacon. The Fig. 6 arrangement may be modified, Fig. 7 (not shown), to simulate a plurality of spaced A-N beacons each having a plurality of marker beacons. In this case the number of contacts on the switch sections W, X, Y, Z is equal to the total number of marker beacons and the outputs from the W and X sections of the switch are applied selectively to a plurality of pairs of range potentiometers R-601, R-602 controlled by separate range servos (one for each A-N beacon) by means of relays controlled by additional sections R, S, T on the selector switch; these relays also control an additional resistance network in series with the altitude potentiometer. Automatic phase control and compensation, Fig. 8. In the Fig. 6 arrangement unwanted variations in the phase of the outputs from the inductive resolver L-1 due to changes in its angular setting are automatically compensated by applying the input to the resolver through a phase shifter R-821, C-805, Fig. 8, controlled by a servo motor 23 responsive to the phase difference between a direct output A from the potentiometer R-602 coupled to one of the resolver output windings and an output B from the selected marker-beaconlocation potentiometer, e.g. R-203, Fig. 6, derived directly therefrom or via a phase Shift circuit C-803, R-812 which is preset to cancel out the average amount of resolver phase shift; the output B must be selected by an additional switch section Y<SP>1</SP> if auxiliary phase shift circuits are included between the marker-beacon-location potentiometer and the corresponding contact of switch section Y, e.g. as in the case of R-205, Fig. 6. An error voltage proportional to the phase difference between the voltages A and B is produced by combining the voltages and applying the resultant to a phase detector 22 together with a reference voltage in phase quadrature with the voltage B, said reference voltage being derived from the source 200 by means of a phas