GB247626A - Improvements in electric system employing space discharge devices - Google Patents

Abstract

247,626. Western Electric Co., Ltd., (Western Electric Co., Inc.). Oct. 17, 1924. Thermionic detectors and modulating systems. -Consists in inserting an impedance in the grid circuit, of a modulating, demodulating or detecting valve, such that during that part of the cycle of the impressed wave which tends to make the grid positive the grid current produced causes a drop of potential across the impedance which drop tends to maintain the grid at its normal value. In the system shown in Fig. 1, the impedance is an ohmic resistance 14 in the grid circuit of the valve 10. The effect of this impedance is to change the top of the normal characteristic curve of the valve to the shape shown in dotted lines in Fig. 3. In the system shown in Fig. 2, the impedance is a valve 18 having its cathode 19 connected to the cathode of the valve 10 and its plate and grid connected together to form an anode which is connected in series with the secondary of the transformer 15 and the grid 13 of the valve. When the impressed oscillation tends to make the grid 13 positive, the valve 18 is a high impedance to the flow of grid current so that the potential drop is substantially wholly across the valve 18. This arrangement causes the top of the normal characteristic curve of the valve to be cut off as shown by the horizontal line in Fig. 3. In the system shown in Fig. 4, the impedance in the grid circuit of the demodulating valve 30 is the secondary winding of the transformer 39 the impedance of which, at the frequencies dealt with, is such as to match the valve impedance between grid and cathode when the grid is negative. The invention is also shown and described applied to systems in which two valves are connected in known balanced relation with respect to carrier and modulating waves impressed in the input circuit and from which side bands only are delivered to a load circuit, the impedance being inserted in each grid circuit. In another modulating system, Fig. 8, a by-pass circuit is associated with the carrier wave. source 72 and the output circuit, whereby energy is transferred by a transformer 82 to the output circuit in out of phase relation with the unmodulated component passing through the valve 80, so that the amplitude of the unmodulated carrier wave is substantially reduced.