GB524550A - Wide band amplifier sytems for electrical carrier-wave signals - Google Patents

Abstract

524,550. Impedance networks ; thermionic generating and modulating circuits. HAZELTINE CORPORATION. July'7, 1939, No. 19898. Convention date, Aug. 16, 1938. [Classes 40 (iii) and 40 (v)] In a wide-band inter-valve coupling for modulated carrier frequencies, in which deadend filters of the kind described in Specifications 524,547, 524,548, 524,549 are used, the dissipation of energy in the dead-end resistance is reduced by arranging that the carrier signals shall traverse a portion of the coupling having a band-pass characteristic of corresponding frequency range, while the dead-end or inactive portions of the coupling are such as to attenuate the signals before they reach the terminating resistance at the dead end. In the band-pass coupling shown in Fig. 1a, the input valve 10 is coupled to the output valve 13 through a network which includes active portions A, B, through which the signals pass, and dead-end portions C, D in which they are attenuated before reaching the dead-end resistances 24, 37, together with one or both of two valves 11, 12, connected at different points of the network to provide two parallel paths for the signals. The networks resemble those described in the Specification referred to above, but transformer couplings are in some cases substituted for inductances, as shown. The phase-shift per section at the mid-band frequency is #/2, so that the waves reaching resistance 37 via valve 11 and valve 12 respectively differ in phase by n and tend to cancel out, to an extent limited by reflection from the end 39 which has a high-impedance termination. The location of the carrier frequency may be located elsewhere than at the mid-band, so as to secure maximum cancellation as determined by the phase-frequency characteristic. It may, in single-sideband transmission, be located near the edge of the pass-band, where the dead-end resistance (such as 37) is in series with high reactance or in shunt with a low reactance. In a modification, Fig. 2a (not shown), the lower portions A, C of the network have low-pass characteristics and only the carrier is fed to valve 10, while a modulating signal is superimposed on it in the grid-circuits of valves 11, 12 which then act as modulators. The low-pass band-width is equal to the high-pass band-width for single-sideband transmission, Fig. 2c (not shown), but only half the low-pass band is used in double-sideband transmission, Fig. 2d (not shown). In a further modification, Fig. 3 (not shown in full) for use as a power amplifier in a transmitter, each of the valves 11, 12 is replaced by a pair of valves coupled through networks having deadend filters, the second of each such pair of valves being a power valve, and the final valve 13 is replaced by the network E, which matches the impedance of a uniform transmission line. A push-pull amplifier may be similarly designed. The valves employed in the above circuits have anode resistances high in proportion to the impedances of the networks, to minimize the signal voltage output from the valves.