Patent GB-792696-A (GB)
Title: Improved apparatus for simulating radio navigational aids
Inventor: SWIFT JAMES WALTER
IPC: G09B9/26
Filed: 1955-10-18
Abstract: 792,696. Electric analogue calculating. systems. COMMUNICATIONS PATENTS, Ltd. Oct. 18, 1955, No. 29644/55. Class 37. [Also in Group XL (c)] In apparatus forsimulating a hyperbolic radio navigation system voltages proportional to the cartesian co-ordinates of the mobile receiver R, Fig. 3, and of the fixed master and slave transmitters M and S are combined to give distance voltages proportional to the distances MR and SR between the receiver and the master and slave stations respectively, said distance voltages being then subtracted to give a control voltage which is applied to the indicator. Voltages proportional to the distance MS between the master and slave transmitters and to the slave transmitter time delay TD are also combined with the control voltage. When simulating a C.W. phase system the control voltage may be applied directly to the indicator but when simulating a pulse system the D.C. control voltage is combined with a sawtooth voltage wave to give a delayed marker pulse for the C.R.T. display. In one embodiment, Fig. 2, x and y A.C. co-ordinate voltages corresponding to the position of R, S and M, as shown in Fig. 3, are produced at the sliders of potentiometers 25, 26; 29, 30 and 27, 28, which are unenergized with A.C. voltages of constant amplitude, potentiometers 25, 26 being energized in opposite phase to the other potentiometers. The sliders of potentiometers 29, 30 and 27, 28 are preset and the sliders of potentiometers 25, 26 are adjusted continuously in accordance with the assumed varying position of R, e.g. in response to the operation of flight controls in a flight trainer. The outputs from potentiometers 25 and 29 are summed in an amplifier 44 giving a voltage proportional to (x3 - x2) which is applied to the stator 42 of an inductive resolver and a voltage proportional to (y<SP>3</SP> - y2) derived from potentiometers 26, 30 and an amplifier 45 is applied to the other resolver stator 43. The resolver rotor 41 is automatically set by a servo (not shown) actuated in known manner by the output from a second rotor (not shown) orthogonal to the rotor 41 such that the voltage induced in the rotor 41 is proportional to SR. A voltage proportional to MR is produced in a similar manner in the rotor 40 of another resolver 38 and after phase reversal in an amplifier 46 is combined with the SR voltage in a summing amplifier 49 to give the required difference voltage (SR - MR) as modified by a voltage proportional to the constant time delay of the slave transmitter S, which voltage is applied to the amplifier 49 over the lead 54. A corresponding difference voltage (S<SP>1</SP>R - MR) corresponding to a second fixed slave transmitter S<SP>1</SP> is produced in a similar manner by x and y co-ordinate potentiometers 56, 57, resolver 60 and summing amplifier 61. In the arrangement shown in Fig. 4, combination of the x and y co-ordinates is effected by adding phasequadrature A.C. voltages. Separate potentiometers are provided for each co-ordinate of the receiver and of the two slaves S, S<SP>1</SP> and two ganged x potentiometers 95, 97 and two ganged y potentiometers 96, 98 are provided for the master. The x and y potentiometers of each station are energized in phase quadrature, the master potentiometers 95, 96 are in phase with the receiver potentiometers 62, 68 and the master potentiometers 97, 98 and the slave potentiometers are in opposite phase to the receiver potentiometers 62, 68. An A.C. voltage of amplitude proportional to SR is produced by summing at point 74 voltages x3 < 0, x2 < 180, y<SP>3</SP>>90, and y<SP>2</SP>>270 from potentiometers 62, 63, 68 and 69 respectively, and the resultant voltage is rectified at 81. Corresponding D.C. voltages MS, MS<SP>1</SP>, S<SP>1</SP>R and - MR are produced in a similar manner at rectifiers 80, 83, 82, and 84, rectifier 84 being reversed in polarity to give the required negative output and the voltages MS, SR, TD, - MR are added at terminal 93 to give one D.C. control voltage; a D.C. control voltage proportional to (MS<SP>1</SP> + S<SP>1</SP>R+TD - MR) corresponding to slave S<SP>1</SP> is produced at terminal 94. In order to simulate changeover from one group of transmitters to another the wipers or tappings of the relevant potentiometers may be changed manually or automatically and the extent of travel of the receiver potentiometer wipers may be limited so that when the receiver moves out of range of a station the control signal ceases. Non-linear potentiometers may be used to compensate for the effects of the earth's curvature and corrections for the altitude of an airborne receiver may be applied.