Patent GB-582795-A (GB)
Title: Improvements in or relating to radio frequency generating and modulating systems
IPC: H03C1/62
Filed: 1942-07-23
Abstract: 582,795. Valve keying and modulating systems. HINGS, D. L. July 23, 1942, No. 10326. [Class 40 (v)] A radio-frequency amplifier for energizing an antenna which may be keyed or modulated and voice controlled comprises a series arrangement of a space discharge tube, a series resonant load circuit and a generator operating at the resonant frequency of the series resonant circuit. Fig. 1 shows an oscillator V coupled to the cathode of an amplifier V1 arranged in series with a choke 11 and a series resonant circuit 20, 21. The amplifier anode supply is fed through choke 18 and the grid 15 is earthed by condenser 12 for radio frequency and fed with modulating potentials at the terminals A, B. The series resonant circuit 20, 21 may be constituted by the distributed capacity and inductance of an antenna. Alternatively, the load may be connected across the capacity or inductance of the resonant circuit. The generator V includes a piezo electric crystal and an aperiodic radio frequency coupling, condenser 10, to the cathode of the amplifier which is earthed through the choke 11 while the anode supply is fed through the choke 9. A small capacity 6 is included in the piezo electric crystal circuit to limit the feedback when the mean modulating potential on the amplifier grid 15 is sufficiently positive to make the amplifier resonant at the crystal frequency. In this way the oscillation amplitude is controlled by the bias applied to the grid 15 of the amplifier V1 whilst control of the generation of oscillations , is effected by controlling this bias as by the arrangement shown in Fig. 5. The modulating signal is also applied to the grid 15 the circuit being completed through condenser 57. C.W. or I.C.W. may be transmitted by keyed bias or an audio voltage. To obtain linear modulation the interelectrode capacity of tube V1 may be neutralized by the condenser 22 which is omitted when the carrier amplitude is varied in accordance with the modulating signal. The system is particularly adapted for use with aircraft since change in operating frequency is effected by changing the crystal and readjusting the length of the aerial or aerial tuning only. A single cathode tube with the cathode arranged between two anodes may be used, Fig. 12, in which case the oscillator anode is earthed and the cathode and amplifier anodes are choke fed. Multi-stage amplification may be effected by series connected parallel pairs of valves V1, V2 and V3, V4, Fig. 11, the cathode of the former being driven by the oscillator V and modulation being applied to the grids of the latter. The output anodes are connected to the series circuit 20, 21, the anode supply being choke fed to a tapping on the inductance 20 to avoid highfrequency loss. Only the stage V3, V4 is controlled so that it is unnecessary to neutralize the stage VI, V2 while screen potentials and anode potentials of the stage V1, V2 are derived from the potential divider 23, 24 and a choke 18 connects the cathodes V3, V4 to the modulating course A, B which is also connected to the grids of the stage V3, V4, while the grids of the stage V1, V2 are held at fixed bias. The tubes V3, V4 are rated at higher power than the tubes V1, V2 and parallel tubes are used in each stage to obtain low impedance. Preferably beam power tubes are used in all arrangements. The Specification gives curves showing modulation with carrier control and with C.W. and I.C.W.