GB453254A - Improvements in or relating to telegraph signalling systems - Google Patents

Abstract

453,254. Alternating current telegraphy; valve circuits. SOC. D'ETUDES POUR LIAISONS TELEPHONIQUES ET TELEGRAPHIQUES A LONGUE DISTANCE, 25, Rue du 4 Septembre, Paris. Nov. 14, 1935, No. 31594. Convention date, Nov. 15, 1934. [Classes 40 (iii) and 40 (v)] Telegraphic signals of opposite polarity are converted to alternating-current signals of constant frequency and opposite phase by means of a symmetrical modulator comprising a bridge of dry rectifiers, the reverse process being accomplished at the receiver by a similar symmetrical demodulator. As shown, the telegraph signals are applied to the points 1, 2 of the modulator 4, the alternating currents being taken from a source 3. At the receiver, the signals after amplification by the triode 11 are applied to the symmetrical demodulator 6 together with an alternating current of signal frequency and constant phase from an oscillator 21 the frequency of which is controlled from the output of a frequency doubler 20 supplied with signal currents from the transformer 19 in the anode circuit of valve 11. For signal level correction a transformer 15 in the anode circuit of valve 11 supplies signals which are rectified by elements 17, 18 and charge a condenser 16 included in the grid circuit of valve 11 to reduce its amplification. The transformer 15 is shortcircuited however by the biassed rectifying elements 12, 13 when the signal level is below a predetermined value. Specification 356,584 is referred to.