GB395840A - Improvements in or relating to wireless signalling - Google Patents

Abstract

395,840. Wireless transmitting and receiving systems. TELEFUNKEN GES. FUR DRAHTLOSE TELEGRAPHIE, 12, Hallesches Ufer, Berlin. May 18, 1932, No. 14174. Convention date, May 18, 1931. [Class 40 (v).] The modulation characteristic of a radio transmitter, i.e. the curve relating aerial current to modulating signal, is arranged to be of exponential form. The demodulating characteristic of the receiver is also preferably of the same form thus ensuring distortionless transmission. The exponential demodulation curve has the advantage that rectified signal strength depends only on depth of modulation so that signal strength is not affected by fading. In Fig. 3, the left-hand curve shows the modulation characteristic of a transmitter with aerial current I plotted vertically and modulating voltage E horizontally, the curve being of the form I =Ae<BE>. The right-hand curve shows the demodulation curve of the receiver, aerial current I being again plotted vertically and the rectified signal current horizontally. Fig. 4 shows a suitable transmitting circuit, in which the wave generator 1 feeds an ordinary modulator 2 receiving its signal voltage at terminals 10. The modulated output is fed to a number of amplifiers 3, 4, 5 connected in parallel but with different bias voltages applied to. their grids from a potentiometer 9. The valves have similar characteristics as indicated by the curves n3, n4, n5 displaced according to their different bias voltage ; and the resultant curve ng is approximately of exponential form. Modulating or demodulating valves may be connected as in Fig. 4 ; or a single variable-mu valve may be used. Specification 393,415 is referred to in connection with the receiving circuit, and super-regenerative reception is also referred to.