GB428708A - Improvements in means for producing electrical oscillations of square wave form - Google Patents

Abstract

428,708. Changing wave-form. GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, London, and ESPLEY, D. C., c/o General Electric Co., Wembley, Middlesex. Jan. 3, 1934, No. 239. [Class 38 (ii)] [See also Group XL] A fundamental input wave of sinusoidal or other form is converted into a square wave-form, for the purpose of generating odd harmonics of the fundamental, by a pair of valves in cascade, the first valve giving an approximately square output wave and the second serving to sharpen the corners of the wave-form. The input from transformer 21 (shown in curve a of Fig. 2) is applied to the grid circuit of the valve 25 through a high resistance 26, the grid being biassed by a potentiometer 33 to a point of low anode current. As the grid voltage tends to become positive, the anode current rises rapidly as shown at AA<1> of curve b of Fig. 2, until grid current starts to flow and prevents further substantial rise either in grid voltage or anode current (see A<1>B<1> of curve b). The input is of large amplitude, so that the rise AA<1> and subsequent fall B<1>B in anode current occupy only small fractions of a cycle. The anode circuit includes a resistance 27, the voltage across which is transferred through a large condenser 30 and a limiting resistance 31, similar to 26, to the grid of the valve 29. This operates in a similar manner to the valve 25 and gives an output voltage of sharply square waveform as shown by curve c of Fig. 2. A constant fraction of this output is applied to a linear amplifier 35, from which it passes through a filter 38 designed to cut off any frequencies not within a desired band of harmonics. The filter also changes the phases of the harmonics so that they can be more efficiently amplified in the following valve 45, as described in Specification 422,977, [Group XL]. The filter terminates in a condenser 42 and resistance 43 which tend to accentuate the weak higher harmonics and bring them all to substantially the same amplitude, as described in Specification 389,917, [Group XL]. The various harmonics are taken off from the transformer 46 for utilization in tone telegraphy &c. Specification 315,791, [Class 40 (iii)], also is referred to.