GB467066A - Improvements in or relating to phase modulating circuit arrangements - Google Patents

Abstract

467,066. Valve modulating circuits. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Oct. 23, 1936, No. 28908. Conventiondate, Oct. 26, 1935. [Class 40 (v)] A phase modulator comprises a "neutralized carrier frequency stage with means for applying modulating potentials to vary the effective neutralization. In one embodiment, Fig. 1, a carrier frequency source 8 feeds the grid circuit of a valve V1, a neutralizing circuit comprising a condenser NC and part of the output coil 4 being provided as shown. A pair of push-pull modulating valves V2, V3, the grids of which are supplied with modulating potentials from a source 7, shunt the impedances Z1, Z2 which together with condensers 3, 31 respectively are connected between the cathode tapping of the coil 4 and its anode and grid ends, respectively. The varying impedances of the valves V2, V3, unbalance the neutralizing circuit and produce regeneration or degeneration as the case may be to advance or retard the phase of the output from the valve V1. The circuit 4 may be tuned to a harmonic of the carrier source. In a further embodiment, Fig. 2, a pair of push-pull valves V1 and V1<1> are fed with carrier frequency from a source 8, one of the valves being under-neutralized and the other over-neutralized by the usual neutralizing condensers NC, NC<1>. Modulation potentials from source 7 are also fed to their grids and the phase of the carrier in the output circuit 4 depends upon the relative outputs from the valves, which depends upon their grid potentials. In another embodiment, Fig. 4, the source 8 is dispensed with and the valves V1, V1<1> are made to oscillate by back-coupling the anode to the grid circuits through a piezocrystal P with its neutralizing condenser FP. The electrical centre of the cathodes may be earthed through a resistance element 36 such as " Thyrite " (Registered Trade Mark) which has a non-linear characteristic of such a nature that a rise of anode current due to accidental cessation of the generated oscillations produces a large change in the grid bias and consequent limitation of the anode current. In a similar circuit, Fig. 3 (not shown), anode modulation is used.