GB608265A - Improvements in or relating to electrical automatic tuning circuit arrangements suitable for use on high frequencies - Google Patents

Abstract

608,265. Phase measurement. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Feb. 8, 1946, No. 4054. Convention date, Feb. 9, 1945. [Class 37] [Also in Group XXXVIII] A circuit is automatically tuned to an injected frequency, a change of which causes the circuit to be reduced to a resonant frequency below the injected frequency so that the circuit cannot be tuned to an harmonic of the injected frequency. Automatic tuning.-An oscillator 10, whose frequency is determined by a replacable crystal 12 and replacable tank circuits 16, 18 feeds an amplifier T2 and a circuit 30 to be tuned; oscillations from circuits 18, 30 are applied to a phase discriminator 60 to render one or other of thyratrons 74 conducting according to which oscillation leads in phase; the thyratrons energize the stator windings 80, 82 of a reversible motor which adjusts the tuning element of circuit 30. When the crystal 12 is removed for replacement, contacts 101 are closed to earth line 102 and the grid 71 of valve 60 over contact 103 so that the motor is driven back to its starting position to stop when contact 103 is opened by the motordriven cam 119. Insertion of another crystal opens contacts 101. Where the circuit 30 is tuned by variation of a short-circuit tapping on an inductance, the short-circuited portion may resonate at the crystal frequency when the circuit 30 is tuned to a lower frequency, thus producing spurious tuning; to avoid this, crystals for frequencies above, e.g. 15 megacycles are arranged to close contacts K<11> to earth the grid 69 of valve 60 over contact 117; the motor thus runs to carry the tuning up to, e.g. 15 megacycles, when contact 117 is opened by a motor-driven cam to place the motor under the control of the phase discriminator 60. A further circuit 50 may be similarly tuned by an assembly 90. Phase discrimination.-Oscillations from circuit 18 are applied over leads L, L1 to the grids 69, 71 of vafve 60 in phase opposition; oscillations from circuit 30 are applied over a 90 degree phase shifting condenser 31 and lead L2 (equal in length to leads L, L1) to the cathode of valve 60; a 60-cycle voltage is applied to both grids 69, 71 over resistance 66, so that the output consists of a 60-cycle current whose phase depends on which of the oscillations from circuits 18, 30 is leading in phase.