GB347984A - Improvements in or relating to high frequency receivers - Google Patents

Abstract

347,984. Wireless receiving systems. TELEFUNKEN GES. FUR DRAHTLOSE TELEGRAPHIE, 12, Hallesches Ufer, Berlin. Aug. 8, 1930, No. 23862. Convention date, Aug. 20, 1929. [Classes 40 (iii) and 40 (v).] In order to eliminate the prolongation of telegraphic signals at the receiver due to " echo effect " marking and spacing frequencies are transmitted, the receiver being capable of separating the two frequencies which are separately rectified and fed to indicating or recording means in such a manner that the first portion of each marking and spacing period actuates the recorder in opposite directions. The Figure shows a receiver in which the marking and spacing frequencies are separated by filters 1, 2, separately rectified at 3, 4, and passed through transformers 5, 6, to further rectifiers 7, 8, the bias on which is such that anode current is prohibited with no signal on the grid. Thus the initial portion of a marking signal from 1 closes the upper contacts of the relay 11, which contacts remain closed until the start of the spacing signal from 2, when the lower contacts are closed. By this means the length of the marking and spacing periods transmitted is faithfully reproduced at the receiver. The condensers 14 . . 17 makes the transformers 5, 6 selective between signal frequencies and higher frequencies due to echo phenomena. In addition, amplification may be reduced after the arrival of each marking or spacing signal and increased when the next signal arrives ; also the receiver amplification may be varied inversely with incoming signal amplitude.