Patent GB-916513-A (GB)
Title: Improved simulated radio navigational aids receiver
IPC: G09B9/26
Filed: 1959-10-28
Abstract: 916,513. Radio navigation trainers. CURTISS-WRIGHT CORPORATION. Oct. 28, 1959 [Oct. 28, 1958], No. 36667/59. Class 40 (7). [Also in Group XXXIX] Relates to apparatus for simulating the reception of audio-frequency modulated signals by an airborne radio direction finder of the type in which the receiver may be selectively coupled to a non-directional aerial, so called " Antenna " operation, or to a rotatable loop aerial which may be adjusted manually, i.e. " Loop " operation, or automatically, i.e. " Compass " operation, to its null position. The apparatus comprises means for simulating the variation in the receiver output due to tuning, effective slant distance S<SP>1</SP> from the transmitter, receiver AGC, the angular posisition of the loop aerial, and, in the case of simulated reception from an A-N beacon transmitter, passage of the aircraft through the cone of silence. The effective slant distance S<SP>1</SP> is equal to the actual slant distance S multiplied by a factor representing the power of the transmitter so that the intensity of the simulated received signal is inversely proportional to S<SP>1</SP>. Means are also provided for simulating the reception of noise and CW signals and for simulating the warm-up time when the receiver is switched on. The essential feature of the invention is that an audio signal corresponding to the transmitter modulation signal is modulated on to a carrier of fixed supersonic frequency and applied to an amplifier and demodulator, the gain of the amplifier being controlled by a signal representing the effective slant distance S<SP>1</SP> and by a signal proportional to the strength of the carrier which is obtained by rectifying the output from the amplifier. The invention is described as applied to flight training apparatus for simulating flight over an area including a plurality of transmitters operating at different frequencies within any selectable one of four frequency bands in which the cartesian co-ordinates of the simulated aircraft position are computed in a known form of co-ordinate computer, Fig. 3 (not shown), and applied to a plurality of coordinate converters, Fig. 3 (not shown), one for each transmitter, each of which produces (1) AC signals X and Y representing the plan distance of the transmitter measured across and along the heading of the aircraft, Fig. 3A (not shown); (2) AC signals H, S and tan e representing the height, slant distance and elevation of the aircraft from the transmitter, the signal S being applied to a potentiometer set in accordance with the maximum range of the transmitter to give an effective slant distance signal S<SP>1</SP>; and (3) a negative D.C. signal D representing the plan distance of the aircraft from the transmitter. The apparatus also comprises a corresponding plurality of audio signal sources and of tuning selector units 41, 42, Fig. 2 (see below). Each tuning selector - unit is set by the instructor in accordance with the frequency and frequency band of the corresponding transmitter and the student sets up the tuning control and frequency band selector of a single tuning unit in accordance with the frequency of a required transmitter. When the frequency band selector of the students unit coincides with that of one of the instructor's units and when the settings of the tuning controls of the two units differ by an amount less than an equivalent predetermined frequency separation, e.g. 2.5 kc/s., a corresponding tuning relay I is energized and an AC TUNE signal is produced of amplitude proportional to the difference in the tuning settings. The apparatus includes a number of relays and for each relay the operating coil is indicated by an underlined capital letter, e.g. T, a normally open contact is indicated by the capital letter alone, e.g. T, and a normally closed contact is indicated by the capital letter with a bar above it, e.g. T. Corresponding signals and relays in the different units corresponding to the different transmitters are indicated by the same letter or legend with a numerical subscript. The three operational modes, " Loop," " Antenna " and " Compass " are selected by corresponding relays A, L and C, Fig. 1 (not shown), selectively energized by a five-position switch such that when the switch is in position ON, A, L or C an ON relay O is energized. Tuning selector, Fig. 2. The instructor sets two ganged 4-position switches 60c and 60b in the tuning selector unit 41 in accordance with the frequency band of the corresponding transmitter and sets a potentiometer 58 in accordance with the frequency in the selected band. The student sets corresponding controls 34 and 32 in the student's tuning unit and the AC outputs from the potentiometer 32 and 58 are combined in phase opposition in an amplifier 52 and applied to an amplifier 74 to give the output TUNE 1  signal of magnitude proportional to the misalignment of the tuning potentiometers 32 and 58. The TUNE 1  signal is also rectified to give a corresponding negative D.C. voltage which is applied to the grid of a valve 82 whose cathode is earthed when the student's and instructor's band selector switches 34 and 60c are in corresponding positions so that when the switches 34 and 60c are in corresponding positions and when the magnitude of the TUNE 1  signal is less than a predetermined magnitude corresponding to the allowable difference in the positions of the tuning controls 32 and 58, the valve 82 conducts and energizes the tuning relay T 1 . In order to provide equal tuning sensitively on the four bands when they are of different width, the switch 60b controls an attenuator in the input of amplifier 74. When the transmitter being simulated is an A-N range transmitter, the instructor operates a switch 91 to energize an A-N relay AN 1 . Generating LOOP signal and indicating loop setting, Fig. 4. The position of the loop aerial is simulated by the angular position of the rotor 116 of a resolver 114 and is shown on the indicator 104. A LOOP signal of amplitude proportional to the misalignment α of the loop from its null position is produced by applying the X and Y A.C. signals from the corresponding co-ordinate converter, Fig. 3 (not shown), through a corresponding T contact to the crossed stator coils 120, 122 of the resolver 114 to give a signal proportional to D sin α which is applied to an amplifier 110 whose gain is controlled by the negative D.C. D signal from the corresponding co-ordinate converter to give the misalignment LOOP signal. In " Compass " operation the LOOP signal is applied through relay contact C and amplifier 108 to a two-phase servomotor 106 which automatically sets the rotor 116 to reduce the LOOP signal to zero. In " Loop " operation the LOOP signal is applied through the relay contact L to the receiver proper, Fig. 5 (see below), and the student adjusts the position of the rotor 116 by applying A.C. voltages to the amplifier 108 by means of a spring-centred switch 119. Receiver proper Figs. 5 and 6.-The audio signal selected by the corresponding T contact is modulated at 134 on to a supersonic carrier, e.g. 40 kc/s., from a carrier oscillator 130 and applied through five variable gain " IF " amplifiers 135-139 to a demodulator 144 and audio amplifier 145, another output from the final " IF " amplifier 159 being rectified and applied (1) as an AVC voltage to the AVC " IF " amplifiers 136, 139; and (2) as a tuning signal to an amplifier and tuning meter 148. A gain-control voltage of magnitude determined by the manual setting of a knob 149 is applied (1) to the AVC " IF " amplifiers 136, 139 in " Antenna " and " Loop " operation; and (2) to the audio amplifier 145 in "Compass" operation. Another output from the carrier oscillator 130 is modulated at 142 by noise from a noise diode or commutator brush motor and applied through an amplifier 143 to the " IF " amplifier 139 and a 900 c/s. CW signal may be applied to the modulator 134 by a switch 140<SP>1</SP>. The gain of the " Signal Strength " " IF " amplifiers 135, 137, 138 is controlled by: (1) a negative D.C. voltage produced by applying the selected TUNE signal to an amplifier 162 and rectifier 164. (2) a negative D.C. control voltage which varies with the plan distance from the transmitter as shown by curve 230, Fig. 6, to give a corresponding receiver response curve 236, Fig. 6, the control voltage being produced by applying the selected effective distance signal S<SP>1</SP> to an amplifier-limiter 172 and rectifier 174 having an output-input characteristic as shown in Fig. 5B. (3) during "Loop" operation, a negative D.C. control voltage which varies with the selected input LOOP signal as shown in Fig. 5A, the control voltage being produced by applying the LOOP signal to an amplifier-limiter 178 and rectifier 180 and superimposing the resultant positive D.C. signal on a- 55v. bias voltage, a clamp 182 being provided to prevent the resultant signal from going positive. (4) during " Antenna " and " Loop " operations, a fixed-3v. bias. When it is required to simulate the cone of silence 222, 224, Fig. 6, of an A-N beacon transmitter, the tan # signal selected by the corresponding AN and T contacts is applied to an " amplitude sensitive amplifier " 186 having an output-input characteristic as shown by the thick lines 192, 193<SP>1</SP>, Fig. 5C, to produce an A.C. control signal which varies with the plan distance from the beacon as shown by curve 232, Fig. 6, which is combined with the A.C. S<SP>1</SP> control signal in a summing amplifier 173 to produce a resultant receiver response as shown by curve 238, Fig. 6. The amplifier-limiter 172 may be replaced by an amplifier whose variable gain is controlled by the output from the rectifier 174. In the " amplitude sensitive amplifier " 186 the tan e signal is applied in parallel to a linear amplifier 187 and an amplitude-limiter 188 having respective characteristics as shown at 191 and