GB475531A - Improvements in or relating to thermionic oscillation generator circuits - Google Patents

Abstract

475,531. Valve circuits for generating oscillations. STANDARD TELEPHONES & CABLES, Ltd., and JACOBSEN, B. B. May 22, 1936, No. 14550. [Class 40 (v)] In a system in which a back-coupled valve generates one or more selected harmonics of a master frequency fed to its grid-circuit, a resistance is shunted across the frequencydetermining circuit to reduce the phase change and/or amplitude change of voltages passing round the feed back loop when the wanted multiple frequency differs substantially from the frequency of the frequency-determining circuit. The arrangement can be made always to generate only an exact multiple of the master frequency however the frequency-determining circuit is tuned. In one circuit, Fig. 1 (not shown), in which only one harmonic is utilized, the harmonic generator is similar to that shown in Fig. 2, the frequency-determining circuit being shunted by a resistance 8, but the coil 2111 is coupled to an amplifier valve through resistance and a circuit tuned to the frequency of the wanted harmonic. In Fig. 2, however, this circuit is omitted and there are present in the output circuit of the valve 12 a frequency equal to that of the harmonic nearest to the resonant frequency of the tuned circuit 3, 2<1> and also, owing to intermodulation between this harmonic and the master frequency MF, the next adjacent harmonics of MF above and below it. The resistance 8 has a lower value than in Fig. 1 (not shown). All three frequencies are directed to their appropriate paths by band filters having coils 23 which are tapped to enable inequalities between the amplitudes of the different harmonics to be corrected. In the design of the filter terminations, account is taken of the dissipation of the coils 23, 19 and preferably the dissipations of the coils form the main part of the filter terminations. The tuned circuits such as 27<1>, 28<1> in the output circuits of the valves 24 energize cross talk between the systems when the arrangement supplies several multi-channel carrier systems. The valve 1 may be so biassed that in the absence of any impulse from MF it would remain quiescent.