Patent GB-779171-A (GB)
Title: Aircraft navigation radio beacon receiver circuits
IPC: G01R17/00
Filed: 1955-02-15
Abstract: 779,171. Bridge measurements; power measurement; fault-testing. STANDARD TELEPHONES & CABLES, Ltd. (International Telephone & Telegraph Corporation). Feb. 15, 1955, No. 4476/55. Class 37. [Also in Group XL (c)] An aircraft radio beacon receiver derives from the received beacon energy two low frequency distinguishable signals having variable parameters of magnitude or phase angle whose departure from a predetermined mutual relationship indicates a departure from course, which signals are coupled into a four-arm bridge circuit having in at least two arms respective thermal elements of temperature variable resistance, an excitation source connected to one diagonal and a sense of unbalance indicator across the other diagonal responsive to the excitation energy, the signal coupling means being such that the temperatures of the thermal elements are varied so as to unbalance the bridge in a sense dependent on the sense of departure of the signal parameters from their predetermined relationship. Fig. 1 shows a power-sensitive bridge circuit responsive to 90 and 150 c.p.s. output signals E1 and E2 from a radio beacon receiver which are comparable for equality to indicate zero deviation from a required flight path. The signals are directly applied to heat incandescent lamp elements 1, 2 in adjacent arms of a bridge completed by resistance arms 3, 4 and balance potentiometer 7 and excited by a unidirectional or 400 c.p.s. exciting voltage V across the diagonal including the potentiometer slider. For equality of the input signals, zero voltage appears across the remaining diagonal, while unequal inputs unbalance the bridge due to unequal resistances of the heated lamp filaments to develop an output voltage representing the inequality in sense or phase sense, which may be applied to operate a flight deviation indicator or automatic pilot. The mixed signals may be amplified in triode 20 (Fig. 2), whose output is coupled to the slider of signal balancing potentiometer 21 whose extremities are respectively connected through 90 c.p.s. and 150 c.p.s. filters to the lamp elements 1, 2, which may be replaced by indirectly heated thermistors (Fig. 3, not shown). The navigation receiver of an omnidirectional radio range system may develop a phase variable 30 c.p.s. signal EV indicating flight deviations which is comparable with a reference phase signal ER in the circuit of Fig. 4; signal EV energizing transformer 30 over series resistance 37 to apply antiphase voltages over condensers 31, 32 to thermal elements 33, 34 of the bridge circuit, while signal ER energizes transformer 35 over series resistance 38 to apply a reference voltage between centre point 30a of the secondary of transformer 30 and the junction of the thermal elements; the bridge being energized in series with resistance 39. Element 33 is energized by the vector difference of EV and ER and element 34 by their vector sum, so that the bridge output is zero when EV and ER are in quadrature and otherwise represents in magnitude and sense or phase sense the phase deviation between the two voltages for energization of a deviation indicator or automatic pilot. Resistances 37, 38, 39 heat thermo-couples 37a, 38a, 39a which energize in series a meter coil 40 which in presence of variable phase, reference phase, and excitation voltages holds an associated alarm flag concealed, while exposing it for failure of any or all of the voltages or thermo-couples, or either thermal element. A bridge comprising indirectly heated thermal resistance elements (Fig. 5, not shown), may be energized by a 400 c.p.s. alternating voltage in shunt with a half-wave rectifier and load resistance producing simultaneous D.C. energization; the unbalance output being  applied to the ends of separate primaries of an output transformer interconnected by a condenser across which a direct unbalance voltage appears to operate an indicator while an alternating unbalance voltage appears across the transformer secondary to operate an automatic pilot. The indicating instrument may be dynamometric with a rotor coil energized from the bridge unbalance and a stator coil energized from the bridge excitation voltage (Fig. 6 not shown). Fig. 7 shows a phase-responsive circuit wherein the 30 c.p.s. variable phase signal is coupled over transformer 71 having a split secondary to a diagonal of a bridge 70 comprising four thermal elements such as lamps; the secondary windings being interconnected by a 30 c.p.s. resonant filter 74 across which is applied a direct and/or 400 c.p.s. alternating excitation voltage. The 30 c.p.s. reference phase signal is coupled over transformer 72 having a split secondary to the remaining bridge diagonal; the secondary windings being interconnected by a 30 c.p.s. resonant filter 76 across which is connected the split primary windings of output transformer 75, interconnected by condenser 77. A direct phase-responsive unbalance voltage appears across this condenser for indicator operation while a 400 c.p.s. alternating phase-responsive unbalance voltage appears across the transformer secondary for automatic pilot operation; the voltage as before being zero for quadrature of the input voltages and representing their phase deviation in magnitude and sense or phase sense. Fig. 8 shows a bridge circuit responsive to 90 and 150 c.p.s. alternating voltage signals E1 and E2 coupled over tuned transformers having centre tapped secondaries to pairs of negative temperature coefficient thermal elements 80, 81 and 82, 83; connected to the bridge between the secondary centre taps and the common return of the elements. The bridge is completed by equal resistances separated by a balancing potentiometer, and diagonal resistances having centre taps across which the excitation and unbalance voltages are developed, while the centre taps 85, 86 are interconnected by a meter coil 84 operating a flag alarm for failure of any thermal element or either signal or excitation voltage supplies.