GB903315A - Improvements in or relating to transmitters for carrier-frequency-shift telegraphy systems - Google Patents

Abstract

903,315. Frequency changing. GENERAL ELECTRIC CO. Ltd. May 4, 1961 [May 6, 1960; April 21, 1961], Nos. 16117/60 and 14433/61. Class 38 (2). [Also in Group XL (c)] In a frequency shift carrier telegraphy system carrier is applied to a resonant circuit 4, 12 with rectifier bridge giving a phase reversible output so that outputs in phase or phase opposition in accordance with Œ D.C. telegraph signals applied at 16 are applied to R-C networks 22, 23 and 19, 28 giving Œ45 degrees phase shift respectively and a rotating electromagnetic field is produced by a pair of crossed coils 30, 31 in the cathode circuits of valves 25, 27. This reverses in direction with the telegraph signals so that from a pick-up coil 35 rotated at constant frequency by a synchronous motor 37 in the field, equal to or a harmonic of the repetition rate of the keying signal, either a sum or difference frequency is produced as output from the transformer coils 36, 38, and used for telegraph signalling. The coils 30, 31 may be wound in two halves on opposite pairs of segments of a ferrite ring 29 (Fig. 2) arranged at right angles. In Fig. 3 (not shown) the oscillator 1 directly feeds C-R and L-R networks producing Œ45 degrees phase shift connected to the two input terminals of the rectifier bridge with output connected to two series connected resonant circuits tuned to the oscillator frequency. Telegraph ŒD.C. signals applied to the junction of the tuned circuits therefore changes by Œ 90 degrees respectively the phase of the quadrature phase oscillations in the tuned circuits and these, arranged at right angles, reverse the direction of the rotating field they produce through a rotating pick-up coil. The quadrature coils may be replaced by arcuate capacitor electrodes, producing a rotating electric field, as in Specification 637,996.