US2290958A - Modulating circuit - Google Patents

Description

July 28, 1942. w. HAGEN MODULATINQGIRCUIT Filed May 12, 1939 Figa Patented July 28.19.42 n

Wolfgang Hagen,

Berlin, Germany, assignor to C. Lorenz Aktiengesellschaft, Berlin-Tempelhof, Germany, a company.

. v Application May 12, 1939, serial No. 273,313

In Germany May 14, 1938' 2 Claims. 'l (Cl. 179-1715) The modulating circuits employed in carrier frequency systems must have a coefficient of non-linear distortion which with a high degree of modulation should be as small as possible. This requirement arises especially in the case ,of the so'ca1led line radio, that is, systems in which speech, music, and the like is transmitted over telephone lines. The modulating circuits used in systems of this kind are in the nature of a bridge connection comprising rectiers or amplifying tubes and have a current-voltage-` The arrangement shown in Fig. 2, is a bridge type modulating circuit fitted with amplifying tubes. Also here the frequency vfl is conveyed over transformer UI to a bridge B While the characteristic which with small values greatly diers from the ideal characteristic necessary for obtaining a small coeflici'ent of non-linear distortion. Therefore in such circuits the rectication in the case of high degrees of modulation, that is to say, in the case of high voltage amplitudes, will fail to be linear, thus producing distortion.

The present invention proposes to provide modulating circuits of this kind with a counter coupling adapted to'render the modulation characteristic linear.

In the accompanying drawing two embodiments of the invention are illustrated.v

Fig. 1 shows the circuit arrangement of one embodiment, while Fig. 2 is a diagrammatic representation of the other.

The modulator here shown comprises an input transformer UI over which the carrier frequency fl arrives, and also comprises rectiers GI, G2, such for instance as diodes or dry rectiflers, and an output transformer U2.. The second or modulating frequency f2 is conducted to the points A. The product of ymodulation of this lbridge arrangement 'is amplified by an electron tube R` and leavesv the modulating arrangement over an output transformer U3.

Part of the output amplitude is conveyed through a phase' and amplitude correcting device X to the transformer UI. The construction elements of the modulator are so calculated that the voltage returned by device X is in phase opposition `with respect tothe input voltage. By

this means a counter coupling is produced that acts to decrease non-linear effects arising in the' modulator.

by way of example frequency f2 is conveyed to this bridge over a transformer U. In the arms of bridge B am- 4 plifying tubes RI, R2, such as triodes, for example, are -included as non-linear members. On l the output side the product of modulation is' derived over transformer U2. The counter coupling is effected by the intermediary of phase and amplitude correcting devices YI, Y2 by which the two sides of the output transformer are connected with the appertaining sides of the input transformer. An arrangement of this kind will not affect the. symmetry of the modulating circuit and also allows of adjusting the properties of thesaid correcting devices independently of each other.

Equally, the modulation may be effected by lmeans of an electron tube arranged to cooperatewith an appropriate counter coupling.

What is claimed is:

1. A modulation arrangement comprising abalanced plurality' of rectifier elements, a carrier input channel including a transformer, a signal input channel, an amplifier having an input and an output; means .for applying carrier Waves from,

said carrier input' channel and signal waves from said signal input channel to said rectifier elements for modulating said carrier Waves by said signal waves, connections fordelivering from ,said elements to the input of said amplier only carrier waves and modulation products, said connections being symmetrically arranged with respect to said signal waves so as to balance these out, and feedback means for feeding back carrier waves from the output-of said amplifier to lreduced.

the primary side o f said transformer in phase opposition to the waves supplied thereto froml said carrier input channel whereby distortion is 2. An arrangement according to claim 1 b wherein said amplier is of unbalanced type and s wherein said feedback means comprises unbalanced connections for effecting said feedback of carrier waves to said primary. A. l .WOLFGANG HAGEN.

Images