GB383180A - Improvements in or relating to electrical high frequency oscillators - Google Patents

Abstract

383,180. Valve generating circuits ; impedance networks. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Marconi House, Strand, London.-(Assignees of Hansell, C. W. ; Port Jefferson, Long Island, New York, U.S.A.) April 20, 1932, No. 11387. Convention date, May 27, 1931. [Classes 40 (iii) and 40 (v).] A piezo-controlled oscillator comprises a screen-grid valve and means whereby the frequency of the oscillations generated is rendered substantially independent of the interelectrode capacity of the piezocrystal. In one embodiment, Fig. 1, the oscillating screengrid valve 34 is shown feeding an amplifier 22, modulator 24, amplifier 30, and radiating aerial 32, and has an input circuit comprising H.F. choke 10 and resistance 2 shunted by condenser 14. The tuned anode circuit 40 is centre-tapped to feed the amplifier 22 through a blocking condenser 44. A feed-back filter circuit 46 is coupled to the anode circuit 40 and comprises a crystal 18 connected between the control grid 6 and one end of the coupling coil 48, the other end being connected through a neutralizing condenser 52 to the other crystal electrode which is also connected to a tuning condenser 54 connected to the centre of coil 48. The choke 10 and condenser 14 in the grid circuit may be omitted. An earthed screen 78 is arranged round the anode circuit 40. In order to match the input impedance of the valve with that of the crystal, the latter may be connected to a tapping on a tuned grid coil, Fig. 2 (not shown), or the choke 10 and condenser 14 being omitted, the resistance 12 may be of the desired order, a grid-biasing potential being added to the circuit. In a further modification, Fig. 3, the crystal 18 is connected between tappings on the plate circuit and tuned grid circuit 49, while a neutralizing condenser 20 is connected to a further tapping on the grid circuit on the other side of the point 51 of substantially zero alternating potential. A further arrangement, Fig. 4, comprises a screengrid valve 2 with a crystal link circuit 46 between tuned anode and grid circuits 40, 74, the link circuit comprising a split input coil 48, crystal 18 and neutralizing condenser 52 and a tuned coupling coil 76, coupled to the grid circuit 74. An earthed screen 78 is arranged round the anode circuit 40. The Specification as open to inspection under Sect. 91 also comprises circuits for triode oscillators. In one arrangement, Fig. 1 (Cancelled), the triode 2 has a tuned anode circuit 16 connected to the grid through crystal 18 whose interelectrode capacity is balanced out by a variable condenser 20 connected between anode and grid, the anode circuit being completed through a centre tapping on the coil of circuit 16, which is inductively coupled to the input coil of amplifier 22. The crystal capacity in another example, Fig. 3 (Cancelled), is balanced by the valve capacity by connecting the anode through the crystal 18, and split tuned circuit 16 to the grid, a variable condenser 56 being provided across the crystal or the cathode tapping 58 being made variable. The output lead 42 may be tapped on to the anode inductance 60. In a modification of this arrangement the anode circuit is tuned and inductively coupled to the output circuit. In further modifications the crystal is connected between anode and grid, the output being taken from a coil coupled to the circuit 16 or from a tapping on a tuned anode circuit. The triode may be neutralized, the anode coil being split for neutralization and coupled to the link circuit through a pair of lines and blocking condensers. This subjectmatter does not appear in the Specification as accepted.