411,644. Wireless transmitting systems. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Electra House, Victoria Embankment, London.-(Assignees of Crosby, M. G. ; 41, 3rd Street, Riverhead, Long Island, New York, U.S.A.) April 11, 1933, No. 10823. Convention date, April 30, 1932. [Class 40 (v).] A short-wave dynatron oscillator is modulated in frequency or phase by applying the modulating voltage or current to a grid within the valve, or to a coil surrounding the valve. The modulating voltage may be distorted by a circuit designed to emphasize the components of higher frequency. The usual dynatron circuit is utilized in Fig. 1 for generating short waves, and speech voltages from a microphone 22 are applied to an auxiliary inner grid 14 through a low-pass filter designed to prevent the carrier wave from reaching the microphone transformer 18. In a modification (Fig. 2, not shown) the microphone is connected through an amplifier to a coil surrounding the valve envelope. In Fig. 4, the negative-resistance effect of the dynatron circuit is supplemented by a coupling capacity C2 between the anode 2 and the inner grid 14. Speech voltages from a microphone 22 are applied to the highvoltage grid 10 as shown, or to the anode 2, or between these two electrodes. The Specification explains that in the case of a short-wave oscillator the speech voltages, by varying the internal capacity of the valve and its internal resistance, cause a variation of the frequency of the wave, although similar circuits used for generating longer waves result in substantial amplitude modulation. Fig. 6 shows a distorting amplifier suitable for interposition between the microphone and the modulator. The plate circuit of the first valve 40 comprises a resistance 41 and inductance 42 in parallel, giving an amplification ratio proportional to frequency ; the voltages are further amplified in a valve 50 before passing to the modulator. Alternative networks for the same purpose comprise (a) a chain of series capacities and shunt inductances (Fig. 5 not shown), (b) a potentiometer feeding the grid circuit of an amplifier through a series resistance and shunt inductance (Fig. 7 not shown) or through a series capacity and shunt resistance (Fig. 8 not shown). In Fig. 7a, a pair of valves is employed with their plates directly connected to each other and to the output transformer 52. Their grids are fed from opposed tappings 54, 54<1> on a potentiometer across the input transformer T, one connection including series resistance 41<1> and shunt inductance 42, the other including series and shunt resistances 41<11>, 43. By varying the positions of the tappings 54, 54<1> the degree of frequency distortion may be controlled. The use of the distorting networks of Figs. 5-8 is stated to render the modulation effectively a phase modulation rather than a frequency modulation.