Patent GB-336721-A (GB)
Title: Improvements in or relating to multi-frequency generators or transmitters
IPC: H04B1/68
Filed: 1929-08-22
Abstract: 336,721. Telefunken Ges. f³r Drahtlose Telegraphic. Oct. 1, 1928, [Convention date]. Fading, preventing; modulating systems. - Two or more high frequencies are generated, particularly for wireless signalling on a plurality of wave-lengths to prevent fading, by coupling two circuits by a single Wheatstone bridge coupling, Fig. 3, which is varied in closeness and sense by subjecting it to a modulating-frequency in such a way that, during a period of the modulating-current im, the coupling factor passes at least twice substantially through zero and alters its direction to produce alternately a lead and lag in the original high-frequency current i1. The unmodulatedhigh-frequency current from terminals p, and the modulating currents from a source d are fed to the bridge at two opposite corners a1, the resulting frequencies are obtained at the two other corners a2, and the resistance of at least one branch is varied about a mean value at which the bridge is balanced. A source b0 of direct current ig, is connected to the corners a2 to pre-magnetize inductances L1, L2 so that they are affected differentially by the modulating-frequency current im to unbalance the bridge. According to modifications to avoid pre-magnetization by direct current, the modulating-current is applied across one only of the inductances, the other then consisting of an aircored inductance (Fig. 5, not shown); the variable resistance effecting the modulation is a valve resistance; the arms of the bridge consist of condensers, one of which is varied at the modulating-frequenoy (Fig 6, not shown). The Specification as open to inspection under Sect. 91 (3) (a) comprises also effecting the coupling by two transformers L1, L2, Fig. 8 (Cancelled), in opposition, only one, L2 of which has a widely variable iron saturation controlled by. the modulating-current im, and at the mean value of the iron saturation, the effects of the two transformers on the output circuit Z cancel one another. In a simpler modification, two circuits L", C", I, Fig. 3 (Cancelled), are connected across a coupling branch which consists of a capacity C in series with an iron-cored inductance L, preferably made of conductors coated with iron. The inductance is controlled, by the modulating-current im in a winding e and is pre-magnetized by direct current ig to such a value that the reactance Xk of the, coupling branch is zero at the frequency of the current il in the circuit L<11>, C<11> when the modulating- current is zero. The high-frequency current i1 is maintained constant by loosely coupling the circuit L<11>, C<11> to a coil L<1> connected to a source q. The resistance Z of the modulated current branch I includes the transferred resistance of an amplifier V coupled through a circuit II. According to modifications: the coupling. branch forks into two equal parallel branches (Fig. 4, Cancelled, not shown) ; the modulating-currents control the capacity of the condenser C (Fig. 9, Cancelled, not shown). This subject-matter does not appear in the Specification as accepted.