Patent GB-555803-A (GB)
Title: Radio compasses
IPC: G01S1/02
Filed: 1942-03-03
Abstract: 555,803. Wireless direction-finding apparatus. STANDARD TELEPHONES & CABLES, Ltd. March 3, 1942, No. 2808. Convention date, March 5, 1941. [Class 40 (v)] A radio direction-finder in which sense ambiguity is avoided comprises pick-up means having a rotary reception pattern, an omnidirectional pick-up means, means for deriving from the received waves signals the envelope of which has unequal maxima and cusp-shaped minima, means for detecting these signals to yield a rotation-frequency modulated wave inverted with respect to the envelope and having alternate cusp-shaped maxima of greater amplitude than the intervening maxima, a cathode-ray oscillograph with perpendicularly-related deflecting means to one of which this wave is applied, means for generating wave energy of the rotationfrequency which is applied to the other deflecting means, and means for eliminating the traces produced on the oscillograph screen by the cusps of smaller amplitude. In the apparatus shown a loop aerial 1 rotated by a motor 2 delivers the received signals, modulated at rotation frequency as shown at I, Fig. 2, to receiving and detecting circuits 7, to which are also supplied signals of lesser amplitude from a non-directional aerial 3. The signals are added in the receiver and detector 7, preferably with the aid of a valve to minimize inter-coupling between the two aerials, to produce the wave-form shown at II, having alternately unequal loops. The rectified output from the detector circuit 7 is shown at III and is predominantly of double the rotation frequency, but alternate loops are of different amplitude due to a component IV of rotation frequency being present. This latter component is passed through a filter 9, phase shifter 10, and amplifier 11, the output from which is shown at V, in which the maxima and minima occur at the minima of the wave III. The inverted output from the detector 7, together with the output from the amplifier 11, are passed to a limiter 12, the wave form due to both being shown at VI and comprising alternate high and low cusps corresponding to the two minima obtained for each rotation of the frame aerial. The limiter passes to the vertical deflecting plates of a cathode-ray tube 13 only signals corresponding to the peaks of the higher cusps so causing only one vertical deflection of the beam for each revolution of the frame which corresponds to the direction and sense of the received signals. The horizontal movements of the beam are produced by a sweep circuit generator 14 such as a rotary rheostat. The cathode-ray beam may be extinguished except when a signal is passed by the limiter 12 by applying the output voltage from the limiter to a modulating grid, or the horizontal trace of the beam may be covered by a mark. The Specification as open to inspection under Sect. 91 refers to forms in which the apparatus 9, 10, 11, 12 is omitted, thus producing a trace on the oscillograph screen similar to curve III, but inverted. If resolution of the 180 degrees ambiguity is necessary, the antenna 3 may be adjusted to feed a substantial amount of energy, but slightly less than that from the loop 1. This results in the alternate loops of curve II being of very unequal size, and the modification of curve III so that it shows pairs of closely-adjacent minima, one of which (for example, the left-hand one) indicates the true bearing. This subjectmatter does not appear in the Specification as accepted.