US1933631A - Compensated circuit scheme for grid direct current modulation - Google Patents

Compensated circuit scheme for grid direct current modulation Download PDF

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Publication number
US1933631A
US1933631A US504584A US50458430A US1933631A US 1933631 A US1933631 A US 1933631A US 504584 A US504584 A US 504584A US 50458430 A US50458430 A US 50458430A US 1933631 A US1933631 A US 1933631A
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capacity
tube
grid
circuit
modulation
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US504584A
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Kummerer Wilhelm
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Telefunken AG
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Telefunken AG
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03C—MODULATION
    • H03C1/00—Amplitude modulation
    • H03C1/16—Amplitude modulation by means of discharge device having at least three electrodes
    • H03C1/18—Amplitude modulation by means of discharge device having at least three electrodes carrier applied to control grid
    • H03C1/22—Amplitude modulation by means of discharge device having at least three electrodes carrier applied to control grid modulating signal applied to same grid

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  • transformer secondary winding does not depend entirely upon the static capacity between the filament and grid of the modulator tube but, rather, is governed by a considerably higher dynamic capacity caused by the appearance of the audio frequency potentials at the terminals of the condenser mentioned above in the grid alternating This audio frequency potential is, of course, on the output electrodes of the modulated stage.
  • Figures 1 and 1a illustrate a system for supplying energy to a bridge arrangement
  • Figures 2 and 2a illustrate an improvement over the arrangement shown by Figures 1 and id for increasing the sensitivenessand balance of the system
  • Figures 3 and 3a illustrate a modification of the arrangement shown by Figures 2 and 2a.
  • T and T1 and T2 respectively, represent the primary and the two secondary windings of the modulation transformer; K represents the filament of the modulation tube M, G the grid element of the tube, and A the plate element.
  • N The point where thecompensating condenser CAN is united with the transformer winding is denoted by N.
  • the grid to filament capacity of the modulated stage supplied from the modulation frequency amplifier of the present invention is indicated by the capacity C, and the grid to plate capacity of the relay tube M is denoted diagrammatically in Fig.
  • FIG. 1a the grid to filament capacity of the modulated tube 1 is connected, as shown, in parallel with the capacity C by way of a conventional input circuit LC.
  • the circuit LC is coupled to any source of sustainedoscillations.
  • a con-v ventional form of oscillation generator including a tube G with coupled input and output circuits.
  • the audio frequency potentials originating in the audio frequency source 'AF are amplified in my balanced modulation frequency amplifier including tube M and applied by way of transformer T and tube-M to the terminals of capacity C ,in the input circuit of tube 1, that is, in the input circuit of the modulated tube, to modulate therein the high frequency oscillations amplified andv relayed by tubal.
  • the modulated oscillations may be utilized in any manner. For example, they may be impressed from a conventional output circuit on to a conventional radiating system. It will be readily seen'by reference to the bridge circuit of Fig.
  • transformers involveinter-turn capacities k and k, as in:
  • the capacity g should be equal to the grid-filament capacity 9/ of the modulator tube,
  • This type-of grid direct current modulator circuit scheme makes it inherently necessary to. ground suitably the point A, i. e., the plate of the modulation tube as shown in Figures 2 and 2a.
  • the middle of the transformer primary winding M is likewise grounded, in other words, joined with A as indicated in Figures 2 and 2a, then the distributed capacity between the windings, which is further increased by the stray inductance of the two halves of primary T which are connected in opposition, would appear as connected in parallel to the grid to plate capacity.
  • This distributed capacity in practical cases, amounts mostly'to a CAN. It may therefore be more favorable to connect M with K by way of ground as shown in Figs.
  • the direct current potential V required for the grid bias of the modulator tubes may be fed in at the 1 middle of the transformer, for instance, through a high-ohm resistance R; also the grounding of the middle of the primary may be effected by way of an exactly balanced resistance P or voltagedividing condenser.
  • the modulator stage of the several figures including the windings T1 and T2 is, as shown, arranged in a bridge circuit so that the capacitive effect of said windings is neutralized and can not be transferred in either direction between the output electrodes and the input electrodes of the modulator stage M.
  • the bridge is not neutralized with respect to the signal currents or potentials applied from the winding T to the windings T1 and T2. This is due to the fact that the winding T1 in the one arm of the bridge is connected between the grid and cathode of the amplifying repeater M so that the bridge is not balanced with" respect to these potentials which appear amplified between the anode'and cathode of the tube M and are consequently impressed across the terminals of the capacity C.
  • circuit schemes have been shown in which voltage division between G, K and N is effected by purely inductive means, as in Figures 1 and la, or purely capacitively, as in Figures 3 and 3a, and the combination of both as shown in Figures 2 and 2a, though always at the ratio of 1:1. Fundamentally speaking, this division could also be at any other ratio as long as the bridge connection is balanced. What is of importance is that the secondary winding of the transformer should be carefully symmetric in reference to the primary end.
  • a balanced modulation frequency amp ifier and a balanced modulation frequency transformer for supplying energizing currents thereto and means for preventing the modulation signal potentials in the output circuit of said amplifier from affectingsaid modulation transformer ineluding, a thermionic tube, a symmetrical secondary winding having two portions, the terminal of one of which is connected to the grid electrode of said tube, a connection between the midpoint of said winding and the cathode of said tube, .a connection between the free terminal of the other .of said portions and the anode of said tube, a neutralizing capacity in said connection, means for connecting a load circuit across the anode cathode impedance of said tube, all of said connections being arranged in a balanced bridge circuit such that the effective capacity of the component circuit over the entire audio frequency band is zero.
  • Signalling means comprising, a thermionic relay adapted to repeat high frequency oscillations, a source of signal potentials, and means for modulating said oscillations at signal frequency including means for preventing the en-" ergy resulting when said oscillations are so mods ulated from reacting on the source of signal potentials comprising, a modulation frequency transformer having its primary winding connected to said signal source and its secondary winding forming adjacent arms of a balanced with electrodes in said thermionic relay.
  • Signalling means comprising, a thermionic relay having input electrodes adapted to'be energized by high frequency oscillations and output electrodesconnected with a work circuit, means for modulating oscillations repeated in said relay comprising, a source of signal voltages, a bridge circuit having one diagonal connected with the impedance between two of the electrodes in' saidthermionic relay tube, said bridge circuit comprising four balanced arms, some of said arms being composed in part of the impedance between electrodes in a thermionic amplifying tube, and means for impressing signal voltages from said source onto the other diagonal of said bridge circuit, whereby the signal voltages impressed on said relay tube are amplified and when impressed from'said bridge circuit onto the impedance in said relay tube can not react on said source of signal voltages.
  • Signalling means comprising, a thermionic relay having input electrodes adapted to be energized at high frequency and output electrodes connected with a work circuit, a source of signal bridge circuit, a diagonal of which is connected potentials, a thermionic tube having its anode to cathode impedance connected with the input impedance of said relay tube, said impedance being in the diagonal of a bridge circuit, a modulation frequency transformer having its primary winding connected to said modulation potential source and its secondary winding forming two adjacent arms of said bridge circuit, the midpoint of said secondary winding being connected to the oathode of said last named tube, one terminal of said secondary winding being connected by way of a compensating capacity to the anode of said last named tube and the other terminal of said secondary winding beingconnected to the control electrode of said last named tube, whereby energy resulting in the output circuit of said last named tube is prevented from reacting on said source of high frequency oscillations.

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US504584A 1929-12-20 1930-12-24 Compensated circuit scheme for grid direct current modulation Expired - Lifetime US1933631A (en)

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