Patent GB-898055-A (GB)
Title: Improved simulated radio navigational aids marker receiver
IPC: G09B9/26
Filed: 1959-10-28
Abstract: 898,055. Radio navigation training apparatus. CURTISS-WRIGHT CORPORATION Oct. 28, 1959 [Oct. 28, 1958], No. 36671/59. Class 40(7). CORPORATION. Oct. Relates to apparatus for simulating the reception at an aircraft of radio signals from  the middle and outer marker beacons of an ILS system or the inner and outer fan marker and Z marker beacons of an A-N range system, such beacons having a vertical radiation beam which is conical up to a pre-  determined height and then cylindrical. As  shown in Fig. 9 an audio signal corresponding to the audio modulation of the required beacon is applied through a variable gain amplifier 120 to aural and/or visual indicators, an A.C. voltage DM representing the effective, plan distance of the aircraft from the beacon is applied through a variable gain amplifier 144 to a rectifier 150 to give a negative D.C. voltage which is applied through a manual sensitivity control potentiometer 154 to control the gain of the amplifier 120 and an A.C. voltage HM representing the height of the aircraft is applied through an amplifier-limiter 166 and rectifier 168 having an input-output characteristic as shown in Fig. 9A to give a negative D.C. voltage which controls the gain of the amplifier 144 so that the audio amplifier 120 is cut off when the effective distance exceeds a critical value which increases with height up to the predetermined height at which the beam becomes cylindrical and then remains constant. In an actual receiver the AGC will cause the receiver output to vary with height as shown in Fig. 9B and this effect is simulated by producing in a function generator 148 an additional negative D.C. gain control voltage which varies with HM as shown in Fig. 9B and which is also applied to the sensitivity control 154. As described the distance and height voltages DM and HM are A.C. but they may be D.C. In the case of fan and ILS marker beacons the horizontal crosssection of the vertical beam is substantially elliptical and the effective plan distance is such that if an aircraft follows a horizontal elliptical path of constant radiation intensity its effective plan distance is constant.  The invention is described as applied to a flight training apparatus for simulating flight over an area including a plurality of ILS and A-N range systems in which the cartesian coordinates x, y, h of the simulated aircraft position are computed in a known form of coordinate computer Fig. 1 (not shown) and applied to a plurality of co-ordinate translators Fig. 1 (not shown), one for each beacon system, each of which produces A.C. signals representing the cartesian co-ordinates X, Y, H and plan distance D of the aircraft relative to the corresponding beacon system, said signals being applied to a corresponding beacon computer (see below) which continuously computes the effective plan distances from the marker beacons. A plurality of audio signals corresponding to the different marker signals are generated continuously and when the simulated aircraft position is within the maximum coverage area of a marker beacon, a corresponding marker relay is automatically energized to select the corresponding distance, height and audio marker signals and apply them to the corresponding inputs in Fig. 9. Component details In Fig. 9 the amplifier-limiter 166 may be replaced by an amplifier whose variable gain is controlled by the output from the rectifier 168. In the function generator 148, Fig. 9, the HM signal is applied in parallel to a linear amplifier 172 and an amplifier-limiter 174 having a gain equal to that of the linear amplifier 172 in its linear response range, the outputs from the amplifiers 172, 174 being of opposite phase and being combined in a comparator 176 to produce an A.C. output related to the input HM as shown in Fig. 9B which is applied to a rectifier 186 to produce the additional negative D.C. gain control signal for the audio amplifier 120. In a first modification (not shown) the amplifier-limiter 174 is replaced by a reference A.C. voltage of fixed magnitude corresponding to the limiting level 180, Fig. 9B, and of opposite phase to the output from the linear amplifier 172 and a relay connects the input to the rectifier 186 to earth or to the output from the comparator 176 according to whether the output from the amplifier 172 is less than or greater than the reference voltage. In a second modification, Fig. 9C, (not shown) the amplifier-limiter 174 is replaced by a "dual slope" amplifier having an input-output characteristic 174 a, b, c, Fig. 9D, the slope of the initial portion 174a thereof being equal and opposite to the slope of the characteristic 172a of the linear amplifier 172 and the abrupt step 174b being produced by a relay when the input reaches the limiting level 180 as determined by comparison with a reference voltage which is also applied to the comparator 176 by the relay in order to balance out the step in the output. The output from the audio amplifier 120, Fig. 9, is applied through a power amplifier 122 to the intercom system for aural indication and also to a rectifier 124 to energize a relay LP to light a lamp 128; alternatively the different audio marker signals are selected by filters 130, 132, 134 and applied to energize corresponding differently coloured lights 136, 138, 140,  A-N range beacon computer, Figs. 2, 3 and Fig. 6 (not shown). In Fig. 2 the four legs of the A-N range are indicated by L1, L2, L3, L4; AN indicates the Z marker which has a circular horizontal coverage and IF indicates the inner fan marker on the L2 leg which has an elliptical horizontal coverage. The cartesian co-ordinates of the aircraft position relative to the fan marker IF measured perpendicular to and along the leg L2 are indicated by XIF and YIF respectively. Data from the co-ordinate translator, Fig. 1 (not shown), is applied to a bearing servo 26 which positions an arcuate potentiometer 30 on a circle 25 centred on AN such that the circumferential position of its earthed centre tap is equal to the bearing #B of the aircraft from AN and the A.C. voltage from the co-ordinate translator representing the distance DAN of the aircraft from AN is applied to each end of the potentiometer 30. Four potentiometer wipers 21-24 are arranged on the circle 25 at positions corresponding to the four legs L1-L4 so that if the aircraft is within a sector of predetermined width centred on one of the legs (L2 as shown) the corresponding wiper 22 will contact the potentiometer 30 to (1) pick off a voltage XIF = DAN #F where #F is the angular displacement of the aircraft from the leg L2 and (2) earth the grid of a valve in a relay control circuit 62 to energize a corresponding leg relay L-2; the other leg relays L-1. L-3 and L-4 are connected in a similar manner to the wipers 21, 23, 24; relay control circuit 61 is shown in full. A.C. voltages representing the radial distances dIF of the inner fan markers IF are set up manually on corresponding potentiometers 81-84, Fig. 3, and the voltage corresponding to the leg with the energized relay is selected by an array 50 of leg relay contacts and combined in antiphase with the voltage DAN giving a voltage YIF which is combined in phase quadrature with the voltage XIF from Fig. 2, the values of the summing resistors 39, 45, 47 being such that the Y voltage is multiplied by a factor equal to the ratio of the major and minor axes of the elliptical coverage and of the fan marker so that the resultant A.C. output from the weighting amplifier 40 represents the effective distance D<SP>1</SP>IF of the aircraft from the fan marker; this output is rectified and applied to a relay control circuit 49 to energize an inner fan relay IF when the aircraft is within the maximum horizontal coverage of the inner fan marker. An outer fan relay OF is controlled in a similar manner by a voltage D<SP>1</SP>OF produced in a corresponding circuit 38. Since the Z marker beam has a circular horizontal cross-section the corresponding effective distance Dz is produced, Fig. 6 (not shown), by combining in phase quadrature the voltages XAN and YAN from the corresponding coordinate translator, the resultant voltage being applied to control a corresponding Z marker relay Z. ILS beacon computer, Figs. 4 and 5 (not shown). In this case the co-ordinate outputs XILS and YILS from the corresponding cocrdinate translator are relative to the touchdown point of the ILS system. The beam of each marker, e.g. the outer marker, has an elliptical cross-section with the major axis perpendicular to the approach path, Fig. 4 (not shown) and the effective plan distance D<SP>1</SP>OILS from the marker is determined, Fig. 5 (not shown), by (1) resolving the co-ordinates XILS, YILS along and perpendicular to the approach path to give components Y<SP>11</SP>ILS and XOILS (2) shifting the origin of the Y coordinate to the marker by combining the Y<SP>11</SP>ILS A.C. voltage in antiphase with a voltage representing the distance d of the marker from the touch down point to give a resultant YOILS and (3) combining the voltages XOILS and YOILS in phase quadrature in a weighting amplifier corresponding to the fan marker weighting amplifier 40, Fig. 3, the resultant D<SP>1</SP>OILS being applied to energize an outer marker relay OILS when it is less than a predetermined value corresponding to the maximum horizontal coverage of the marker.  A corresponding circuit is provided for the middle marker, the resolver being common to both circuits.  Selection of distance, height and audio signals. When the simulated aircraft position is within the coverage area of a beacon the corresponding effective plan distance signal is selected by an array of contacts of the relays IF, OF, Z, MILS and OILS, Fig. 7 (not shown), and applied to the DM input of the amplifier 144, Fig. 9; a corresponding height signal for application to the HM inputs of the amplifier 166 and function generator 148