US1940423A - Modulation - Google Patents

Description

W. KUMMERER Dec. 19, 1933.

MODULAT I ON Filed Feb. 17, 1 932 a Jazz re INVENTOR WILHELM KUMMERER BY 0% 8m ATTORNEY Patented Dec. 19, 1 933 MODULATION Wilhelm Kummerer, Berlin, Germany, assignor to Telefunken Gesellschaft fiir Drahtlose Telegraphic in. b. H., Berlin, Germany, a corporation of Germany Application February 17, 1932, Serial No. 593,448, and in Germany February 14, 1931 2 Claims.

This invention relates to signalling and in particular to means for stabilizing the carrierwave amplitude in line-supplied radio-telephony transmitters.

5 For the purpose of insuring distortionless modulation the stabilization of the center line,

i. e., the carrier-wave power in radio-telephony transmitters is very important. When supplynetworks subject to marked fluctuations are m dealt with frequent readjustment is inevitable.

Now, this re-adjustment according to the present invention is to be replaced by automatically operating regulator means. In the presence of constant biasing potential at the modulator tube, the center line adjustment of the transmitter will gradually rise as the supply-line potential rises. If the biasing potential 'of the modulator tube is also derived from the network by way of a rectifier this will spontaneously occasion a certain compensation of the ensuing fault. According to the accidental properties and the slope of the telephonic line, i. e., the characteristic representing the inter-dependence of the radio frequency line current and the audio frequency modulation potential, either an overor an under-compensation may be caused by the fluctuation of the grid biasing potential being proportional to the network fluctuation.

Now, according to the present invention, there is provided in series with a constant biasing potential either positive or negative, an additional grid biasing potential derived from the supplyline which is proportional to the network potential, the said biasing potential derived from the supply-network being made so high that there will just be insured a compensation of the fluctuation about the middle line in the transmitter due to fluctuations in the line supply. If desired, 40 the said constant electromotive force may likewise be taken from the supply-line by way of an interposed regulator device, such as a special transformer having an over-saturated iron-core.

One embodiment of the arrangement here disclosed shall be further described in more detail by reference to the attached drawing in which is shown a circuit diagram of a signalling system including a thermionic oscillation repeater, modulating means, and means for compensating in said system fluctuations in amplitude of the modulated carrier resulting from fluctuations in' the potential applied to the circuits from the energizing source. 1

Referring to the drawing, 1 is the separately excited oscillator which has its plate potential furnished from an alternating current source by way of an alternating current network 0 and a rectifier 3, and its radio frequency excitation from a source 10 by way of oscillations in a transformer. The modulation of this tube 1 is effected by the aid of a modulator tube 4 which is included in the grid circuit of the main tube 1 and in parallel relation to the grid condenser 2 thereof. The resistance of tube 4 is altered at the rate or rhythm of the voice currents impressed on the grid electrode of tube 4 from the modulation transformer 5 connected with the modulating source 12. 7

According to the present invention the biasing potential of the modulator tube 4 consists of two series direct current potentials. One thereof is furnished from a constant source, e. g., battery 6, and the other one from the output electrode of a rectifier '7 whose input electrodes are energized by current from the alternating current network 0. The rectified potential supplied by this source 7 is of course varied conjointly in unison with variations in the network potential. The rectifier 7 in the simplest scheme may consist of the impedance of a one way valve 8 in parallel connection with a smoothing condenser 9.

Having now described my novel modulating scheme and the operation thereof what I claim 1. Signalling means comprising, a source of high frequency oscillations, a thermionic amplifier having a control electrode, a cathode and an anode, a circuit including an inductance connected between the control electrode and cathode of said tube, said inductance being coupled to said high frequency source, a thermionic amplifier having its anode to cathode impedance connected in series in said last named circuit, a thermionic rectifier having its output electrodes connected by way of a filter circuit to the control grid and cathode of said amplifier, a source of direct current potential in one, of said connections, a transformer having its secondary winding connected in one of said connections and its primary winding connected with a source of modulating potential, a second rectifier having its output connected with the anode of said first named amplifier, a source of alternating current, and means for coupling said source to the input circuits of both of said rectifiers, whereby pulsations applied to the anode circuit of said amplifier by said second named rectifier are compensated by pulsations input electrodes of said second named tube, and a device "for compensating the effect of variations in the alternating current source on the modulated carrier in said output circuit including, a plurality of sources of potential connected between the input electrodes of said second named tube, one of said sources including the output electrodes of an additional rectifier, and. acircuit for energizing the input electrodes of said additional rectifier by alternating current from said alternating current potential source.

WILLIAM KUMMERER.

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