Patent GB-584573-A (GB)
Abstract: 584,573. Phase-difference measurements. SVENSKA AKTIEBOLAGET GASACCUMULATOR. Jan. 4, 1945, No. 367. Convention date, Jan. 4, 1944. [Class 37] One of two voltages the phase difference between which is to be measured is fed to the deflecting plates of a cathode ray oscilloscope in the form of two voltages in quadrature so as to cause rotation of the beam to form a circular trace, whilst the other voltage at its maximum value is arranged to cause a deviation of this trace from the circular form. Fig. 1 shows an arrangement for measuring the phase difference between the E.M.F.'s induced in two frame antennae 10, 11 for reading a radio direction. The antennae 10, 11 are connected to the primary windings of tuned transformers 13, 14, the secondary windings of which are connected to the inner control grids of the valves 15<1>, 15<11>, 16<1>, 16<11> of two balanced modulators. The outer control grids of these valves are connected to an A.C. source 17 by means of a transformer 18 and a 90‹ phasechanging filter comprising condensers 19, 20 and resistances 21, 22. The junction of the resistance 21 and condenser 19 is connected to the outer control grids of the valves 151, 1511 whilst the junction 20, 22 is connected to the outer control grids of the valves 16<1>, 16<11>. The anode circuits of the valves 15<1>, 15<11> and 16<1>, 16<11> are connected in push-pull to the primary windings of transformers 23, 24 of a transformer 25, to which an antennae 26 is connected by means of a winding 27. The secondary winding 28 is connected to an amplifier 29 the output of which is fed to a 90‹ phase displacing filter formed by condensers 30, 31 and resistances 32, 33. The voltage from the filter is fed to the control grid of a valve 34. The amplifier 29 is also connected to an output transformer 35 supplying two triode-rectifier valves 36, 37. An anode resistance 38 is common to the valves 34, 36, 37, a voltage with a sharply marked maximum being formed across its terminals.. This voltage is fed to a rectifier valve 42 which is biassed by a battery 43 so that current flows only during a short interval at the maximum of the voltage across the resistance 38. A pair of modulator valves 39, 40 are fed with the voltage from the load resistance 41 of the valve 42 and also with voltages in quadrature derived from the filter 19-22. The anodes of the valves 39, 40 are coupled to the deflecting electrodes of a cathode ray tube 44 and produce on the screen a circular pattern 62, Fig. 2, with a deviation 47 corresponding to the instant at which the voltage across the resistance 38 exceeds the bias from the battery 43. A scale 48 is provided on which the incoming direction of the radio wave may be read directly. In a modification, Fig. 3, the end of the secondary winding of the transformer 35 are connected to the anodes of two rectifiers 36, 37, the centre point being earthed through a resistance 50. A condenser 49 is connected across the valve 36. The upper end of the resistance 50 is connected to the control grid of a triode-rectifier valve 51 provided with such a bias from a battery 52 that anode current only passes in the immediate vicinity of the maximum voltage. This anode current passes through a series resistances 53 and momentarily decreases all the electrode voltages of the cathode ray tube 44 when current is passing through the valve 51, the speed of the electrons being thereby decreased giving an increased power of control of the deflection electrodes. Rotation of the beam is effected by feeding the deflection electrodes through condensers 54, 55 with voltages in quadrature.