Patent GB-481343-A (GB)
Title: Improvements in or relating to radio and like transmitters and circuits and devices suitable for use therein
IPC: H03B5/18
Filed: 1937-05-06
Abstract: 481,343. Valve circuits ; electric resonators. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. May 6, 1937, No. 13013. Convention date, May 6, 1936. [Classes 40 (iii) and 40 (v)] A push-pull short-wave master oscillator MO, whose frequency is controlled by a resonator 11 of the coaxial-cylinder type, feeds a push-pull power amplifier PA in common with a modulation-amplifier MA. Couplings 8, 18, 32 of the Lecher-wire type and a monitoring circuit 35, 36 are provided. Valve circuits. The push-pull master oscillator MO has coils 4 in its filament circuits and byepass condensers 5 for the high frequency. Its frequency is stabilized by a coaxial-cylinder oscillator 11, a shunt loop 8 being added in parallel to reduce the inductance of the grid circuits and keep the regeneration in proper phase. The plates are coupled to a push-pull power amplifier PA through a screened Lecher-wire coupling 18 whose electrical length is made equal to one eighth of the wave-length in order to prevent the power amplifier from loading the oscillator. Television signals from a modulation - amplifier MA are applied to the valves of the poweramplifier PA in parallel, the plates of the final valves in the amplifier MA being kept at + 250 volts with respect to earth while the cathodes of the amplifier PA are at + 500 volts. The amplifier MA, which comprises two single-valve pentode stages 38, 39 together with a pair of pentodes 40 is parallel, receives television signals from a source at V1 ; its output connection is shunted by resistance 42 and an inductance 43 to compensate for inherent capacity, and includes a resistance 41 to prevent pushpush oscillations in the amplifier PA. The output of the amplifier PA is applied to an aerial circuit T through a Lecher-wire system which steps down the voltage to a monitoring system comprising a valve 33 which feeds a meter 36 through a filter 35. Electric resonators. The resonator 11 comprises a pair of coaxial cylinders 9, 10 joined at their lower ends and tuned by varying the capacity between the top of the outer cylinder and two semicircular plates 12, 13 at the top of the inner cylinder ; for this purpose the plate 12 can be made to overlap the plate 13 more or less by turning a screw 14. The resonator is coupled to the push-pull valves 1, 2 by two single-turn coils. The coupling between the oscillator MO and amplifier PA comprises a parallel-tuned circuit consisting of the condenser 17 and copper-rod inductances 18, 18 within coaxial earthed cylinders 19, 19, the ends of the rods 18 being connected by a conductor 44 whose capacity per unit length is matched to that of the rods 18 by positioning it over an earthed sheet 20 ; the conductor 44 serves for an output coupling, and the electrical length of the coupling system is made to be one-eighth of a wave-length, so that the oscillator MO may not be loaded. The output coupling of the amplifier PA comprises two equal Lecher-wire loops 28, 28<1>, connected in parallel for the sake of symmetry, and shunted by a tuning-condenser 29. The loop 28 is coupled through a loop 30, which is symmetrically earthed at 31 to suppress push-push oscillations, and a quarter-wave-length loop 32 to an antenna or like circuit at T. The loop 32 acts as a stepdown transformer for connecting a monitor circuit 33, 35, 36 without imposing a load on the antenna.