GB540773A - Improvements in or relating to radio transmitters for ultra-high frequencies - Google Patents

Abstract

540,773. Electric resonators; wireless signaling. ELECTRICAL RESEARCH PRODUCTS, Inc. May 24, 1940, No. 9180. Convention date, July 26, 1939. [Classes 40 (iii) and 40 (v)] In an ultra-high-frequency transmitter tuned by Lecher wires, the effective length of the wires 16, 17 is varied by axial adjustment of a third parallel conductor 30; the earth connection of the cathode 11 is tunable at 37, 38; frequency modulation is effected, for a distance-indicating system, by rotation of a condenser plate 25 by a motor 26, and the earthward capacitive path through the bearings of the motor is short-circuited by capacity at 57 to eliminate fluctuations of output ; the coupling of the transmitter to the aerial can be varied by deformation of a loop 19 ; and the transmitter is enclosed in an earthed conductive casing 18, the parts being adjustable from outside the casing. The oscillator valve 10 is tuned by screwing the earthed rod 30 in or out so as to vary the length of the part of it which is adjacent to the Lecher wires 16, 17. These terminate in plates 48, 50 which are insulated from the casing 18 by mica, so as to form bypass condensers, and are connected respectively to the anode battery 44 and variable grid-leak resistance 46. The filament current is drawn from a battery 36 through a co-axial line 34 which is somewhat less than a quarter of a wave-length long and has its inner and outer conductors connected respectively to plates 71 and 52 which form byepass condensers with the casing 18, while the outer conductor is also capacitively earthed through a pair of plates 37, 38, the latter of which is earthed through a bearing 43, can be moved axially by means of an insulating rod 40, for the purpose of tuning the connection between filament and earth, and is frictionally held by a fibre bush 42. The frequency of the oscillator may be tested by means of a wavemeter 63 which is connected to the outside of the co-axial line 34 at a suitable point through resistance 73. The frequency is modulated by a rotating condenser 25 driven by a motor 26, but the capacitive earthward path through the ball bearings 56 tends to cause fluctuations in the amplitude of the output; this effect is prevented by a short-circuiting condenser which comprises an outer fixed and earthed cylinder 58 and an inner revolving cylinder 57 mounted on an insulative upper portion 54 of the shaft. The antenna circuit comprises a dipole antenna 21 fed through a co-axial line 20, and a second length 22 of co-axial line having a short-circuiting plug 23 whose position can be adjusted by means of a knob 24 for the purpose of tuning the aerial circuit. The latter is connected to the Lecher wires 14, 15, and so to the valve 10, through a deformable U-shaped loop 19 which is joined to the inner conductors of the co-axial lines 20, 22 and can be bent into or away from the plane of the Lecher wires by means of an adjusting-nut 70. Specification 533,538 is referred to.