GB478849A - Improvements in or relating to radio and other high frequency transmitters - Google Patents

Abstract

478,849. Valve circuits. TELEFUNKEN GES. FUR DRAHTLOSE TELEGRAPHIE. Nov. 30, 1936, No. 32833. Convention date, Nov. 30, 1935. [Class 40 (v)] In an ultra-high-frequency power amplifier in which the capacities of the electrodes are balanced with respect to earth by a neutralizing circuit, which may be a second valve, the capacities in question are reduced by connecting the anode of the valve directly or through a large condenser to the corresponding point in the neutralizing circuit, the cathode lead is formed as a tubular conductor coaxial with the grid lead, and the aerial feeder is matched in a special manner. This arrangement enables valves having external anodes to be used. In a known circuit, Fig. 1a, C1, C2, C3 represent the inter-electrode capacities of the valve R, which is driven from a source of oscillations connected at 1, 2, while C4 represents the capacity of the anode with respect to earth. The dimensions of the tuning inductances LI, L2 for a given frequency are limited by these capacities, and according to the invention the latter are reduced by connecting the anode of the vaive R either directly or through a large condenser C, Fig. 3, to the anode of the capacitycompensating valve N or to the corresponding point in the equivalent condenser network. At the same time the grid and cathode leads gl, cl are coaxially arranged, with the grid lead inside, in order that the earth-capacity effects of these leads may be neutralized. The circuit is tuned by adjusting the length of the part containing the grid lead, which may be coiled or may have a trombone slide. In the case of the amplifier shown in Fig. 3, the cathode-heating and grid potentials are applied at a symmetrically situated point P. Insertion of the condenser C lowers the series capacity of the oscillatory circuits ; C may have a large capacity if the power factor of the load circuit is kept down. For this latter purpose the surge impedance of the aerial feeder is so arranged that the impedance facing left from a point a distant #/4 or (2n+1)#/4 from the transmitter is matched to the surge impedance facing right at that point. The actual impedance W1 facing left is greater than that W2 facing right, and the impedance W2 can be adjusted, for instance, by varying the distance between a pair of conductors.