GB141732A - - Google Patents

Abstract

141,732. Western Electric Co., (Assignees of Bijl, H. J. van der). Aug. 21, 1915, Convention date]. Wireless telephony and telegraphy.-High frequency oscillations are modulated in accordance with low-frequency signals by impressing both potential variations in series on the grid circuit of a thermionic valve, the output circuit of which is coupled to the transmitting-aerial or to a wire conductor. The plate circuit of the valve 2 includes a source 8 shunted by a condenser 9 and is coupled to the transmitting circuit by the transformer 19. The grid circuit of the valve comprises a secondary coil, coupled to the circuit of the high-frequency generator 14, and an adjustable portion of a resistance 10 connected across the secondary of a. transformer 17. The microphone 15 (or an interrupter and key) is in the primary circuit of the. transformer 17. A battery 7 maintains the grid normally at a negative potential relatively to the filament. The high-frequency oscillations are amplified by the valve, and the degree of amplification is determined by the slope of the valve characteristic. This slope varies with the grid potential and therefore with the potential applied by the transformer 17. Preferably the working portion of the characteristic is of parabolic shape, thus giving a slope (or amplification) proportional to the abscissa (or grid potential). The potential applied in the grid circuit bv the signal currents should be large compared with that applied by the high-frequency source, preferably from three to ten times as large.