GB448043A - Improvements in or relating to carrier wave signalling systems - Google Patents

Abstract

448,043. Modulating systems. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Electra House, Victoria Embankment, London. (Assignees of Lindenblad, N. E. ; Port Jefferson, New York, U.S.A.) Nov. 29, 1934, No. 34364. Convention date, Nov. 29, 1933. [Class 40 (v)] A carrier wave generator is varied in frequency by a modulating signal which is distorted in amplitude before being applied to the generator in order to obtain ultimately a linear relation between variation of modulating voltage and variation of carrier frequency. As shown in Fig. 1, the carrier is generated by a valve oscillator 6, controlled by a crystal K. The signal from a microphone 2 or other source is amplified at 4 and passes through a condenser 7 to a potentiometer P, which is also traversed by direct current from a source G feeding through a choke L. A portion of the potentiometer P is tapped into the grid circuit of a valve 8, the cathode lead including a resistance R which lies both in the grid and plate circuits of the valve. The resistance R is also in the grid lead of the oscillator 6, and applies modulating voltage to that grid distorted in such a way as to compensate for the non-linear relation between grid voltage and frequency of the oscillator. Frequency-multipliers 10 may be interposed between the oscillator 6 and the aerial. Alternatively the modulating signal may be distorted by passing it through an amplifier working on a non-linear part of its characteristic, Fig. 4 (not shown). In Fig. 5 the signal voltage is applied across a resistance 11 and biassing-source PS, which are shunted by resistances in series with the plate-cathode path of a triode valve 5. Distorted signal voltage is taken off by a tapping on the plate resistance and is applied through a high-frequency choke I to the plate of the back-coupled crystal-controlled oscillator 13. In Fig. 7, the signal is applied through a condenser 7 to a resistance R1 in series with a non-linear element 18, the resistance of which falls off as the applied voltage rises. Direct current is also passed through the resistances from a source G feeding through a choke L. Distorted signal voltage may be applied to the grid of the oscillator 6 by connections taken off as shown across the resistance R, or alternatively across the non- linear resistance 18 and a portion of the resistance R1, Fig. 6 (not shown). In another arrangement, the signal is applied through a transformer and series condensers to the terminals of a non-linear resistance, which terminals are in the grid circuit of the carrierwave oscillator. The resistance is also traversed by direct current supplied from a source through a series resistance, Fig: 8 (not shown). Fig. 9 shows a tone-frequency generator comprising a back-coupled screen grid valve 28 controlled by a keying-valve 38. The keyed tone-frequency may be used in place of the microphone, or it may be passed to one or more stages of frequency multiplication before being so used. By passing the tone-frequency through a non-linear resistance 48, harmonics are created which may be either amplified or again multiplied in frequency by the valve 41. A further multiplying-stage may comprise a shunt circuit including a non-linear resistance 45 and a variable resistance 51, and this may be followed by a tuned output amplifier 54. Specification 431,526 is referred to.