GB355164A - Improvements in or relating to high frequency signalling systems - Google Patents

Abstract

355,164. Multiplex wireless signalling. TELEFUNKEN GES. FUR DRAHTLOSE TELEGRAPHIE, 12, Hallesches Ufer, Berlin. Jan. 5, 1931, No. 387. Convention date, Jan. 3, 1930. [Classes 40 (iii) and 40 (v).] In the simultaneous transmission of code and copying telegraphy over a single high-frequency channel, a carrier frequency modulated in accordance with the picture signals is alternated between two frequencies to form the code signals. The amplitude of the currents passed from a valve generator 1 to an amplifier 5, a modulator 6, and a transmitter 7 is controlled by a photo-electric cell 4 receiving light from the object, and the frequency of the generator is controlled by a signalling key 2 in series with a condenser 3 across the generator. Alternatively, the carrier frequency is produced by a shutter, perforated disc, Kerr cell, or other light relay in the path of the light scanning the object and controlled in accordance with the code signals to alternate the interruption frequency between two values. In the case of the rotating perforated disc, two rings of holes are provided, each comprising a different number. To prevent loss of code signals when there is no picture current, the code signals may be' transmitted a plurality of times ; or the carrier frequency is never reduced to zero, and at the receiver, Fig. 2 (not shown), a device in the copying telegraph channel has a threshold response, which is automatically varied according to the strength of the incoming high frequency energy.