GB675086A - Balanced electronic modulator - Google Patents

Abstract

675,086. Modulating systems; radio directionfinding. STANDARD TELEPHONES & CABLES, Ltd. Sept. 20, 1946 [May 7, 1945], No. 28301/46. Classes 40 (v) and 40 (vii). A balanced modulator 1 for modulating energy from a first source 2 with energy from a second source 3 comprises a cathode follower circuit 12 and an anode loaded circuit 11, each of the circuits including an electron discharge device having an anode, cathode, and control element, the source 2 being coupled to the control elements 7 and 8 in parallel and the outputs of the two circuits also being connected in parallel to output terminal 15; the second source 3 supplies balanced voltages in phase opposition to the two circuits, through resistors 22 and 23. If the second source 3 supplies rectangular pulses 180 degrees out of phase over the lines 20 and 21 the modulator may be made to act as a phase reversing switch for the energy from source 2. An electronic switch of this type may be used in a radio direction finder in which signals from a rotatable loop 24 and an omnidirectional sense aerial 28 are combined and the phase of the connection of one of the aerial inputs alternately reversed in phase to switch between different directional reception patterns. Such a direction-finder normally includes an electronic switch 34 synchronized with the switching of the direction patterns so that the amplitude of the signals received over the two patterns may be compared by means of an indicator 37. In Fig. 2 the sense aerial is connected to a phase-reversing switch 30 comprising circuits such as are shown in Fig. 1 and rectangular switching wave pulses are applied from control source 31 to alternately render the circuits 11 and 12 thereof effective and so reverse the phase of the output. The output of the receiver 26 is synchronously switched by electronic switch 34 also controlled by the switching waveform from source 31 to the two inputs 35 and 36 of the indicator. A similar direction-finder, Fig. 3 (not shown), is described in which the output of the loop aerial and not of the sense aerial is reversed in phase by the switching. As the loop aerial is balanced with respect to earth the reversing switch is preferably so balanced as well and for this purpose two switches of the type shown in Fig. 1 are connected one in each line and the switching waveform applied to each, Fig. 4 (not shown).