US2224690A - Modulated carrier wave transmitter - Google Patents

Description

L. T. MOODEY ETAL MODULATED CARRIER WAVE TRANSMITTER Filed Dec.

Dec. 1o, 1940;v

Patented Dee.1o,194o y f 2,224,690 Y l UNITED STATES PATENT. orrlcE MODULATED CARRIER WAVE TRANSMITTER Leslie Tyrrell Moodey andCyril Robert Staines,

Chelmsford, England, assignors to Radio Corporation of America, a corporation of Delaware Applieetien -neeember 9, 193s, seriel'Ne. 244,738 In Great Britain December 23, 1937 1 Claim. (Cl. 17975-1715) This invention relates to modulated carrier C4. The third grid G3 is connected to the cathwave transmitters and has for its object to proode K through a resistance R3 in series with a vide improved modulated carrier wave transmitbias source B2 in series with a condenser C5 ters of the so-called oating carrier type, i. e. (in the order named) said resistance and said of the type wherein the carrier level is automatibias source being shunted by condensers C2, C3 5 cally varied in dependence upon the level of the respectively. Modulating potentials are applied modulation signals. from a source MT across the series circuit con- As will be seen later the invention provides sisting of the resistance R3 and bias source B2 improved modulation circuits wherein the carrier and a uni-directional potential obtained in any lo to be modulated is applied to one electrode and convenient manner known per se and varying in 10 the modulating signals to another electrode of dependence upon the modulating potential level,

a tube from whose output circuit modulated caris applied across the condenser C5 at the terrier is obtained, said electrodes beingfscreened minals FCT. Thus modulating potentials with from one another so that the modulation process the uni-directional potential superimposed, are

l5 is eiected substantially only electronically. The applied to the third grid G3. The anode A of 15 invention enables oating carrier control to be the tube is connected to the positive terminal effected in a modulation circuit of this nature of the high tension source through a parallel Without materially adding to the complexity of tuned carrier frequency output circuit CILI, Athe circuit and offers the important rpractical modulated carrier output being taken off from advantages of simplicity and eniciency. across this circuit, e. g. as shown by means of 20 According to this invention a modulation cira C011 OC Coupled to the inductance Ll. cuit arrangement of the oating carrier type In the modification shown in Figure 2 the comprises a tube having a cathode, an anode modulating potentials are applied to the anode and at least three grids in succession therebe- A instead of to the third grid G3. In this moditween, one of said grids being arranged to act cation the third grid G3 iS COlneCted t0 the 25 as a screen grid, means for applying carrier pocathode K merely through the bias source B2 tential to a grid on one side of said screen grid, and condenser C5 in series and the uni-direcmeans for deriving a uni-directional potential tional potential is applied across this condenser varying in dependence upon the modulating po- C5 as before, the said third grid G3 being contential level from the modulating potentials, and nected to earth through a by-pass condenser 30 means for applying said derived potential and C23. The potentiometer resistance RI, instead modulating potentials either to a common elecof being connected directly at one end to the trode on the other side of said screen grid or positive terminal of the high tension SOUICG, iS the derived potential to one and the modulating Connected t0 Sad terminal through a choke L3,

potentials to the other of two electrodes which and modulating potentials are applied over lead 35 are both on said otherside of said screen grid. MP to the junction point J of said choke L3 The invention is illustrated in the accompanywith said potentiometer resistance Rl, said juncing diagrammatic drawing. l tion point being connected, through the output Referring to Figure lwhich shows one embodituned circuit LlCI, to the tube anode A. In

ment the iirst grid Gl (counting from the cathother respects the circuit arrangement is as in 40 ode) of a pentode tube V is connected to the Figure 1. earthed cathode K thereof through a choke L2 The uni-directional potential by means of in series with a resistance R2 in. series with a which the floating carrier control is obtained may suitable bias source BI. The carrier wave to be be derived in any convenient manner. For exmodulated is applied at terminals CT between ample., as shown in Figure 3 modulating .poten-y 45. the first grid Gl and the cathode K. The sectials, ai'ter such amplification as may be desired ond grid G2, which is theA screen grid, is con- (in Figure 3 a single stage amplier AA is shown) nected to Aan adjustable tap T upon a potenimay be rectied by a suitable full wave rectifier ometer resistance Rl which is connected across circuit--shown as a rectiner arrangement coma source (not shown) of high. tension whose terprising two diodes DI, DZf-the capacity shunted 5o minals are indicated by the and signs and load resistance LR of which is included in the whose negative terminal is earthed. This tapgrid circuit of a direct current amplifier valve ping point T is connected to earth through a by- DCA whose anode circuit includes a resistance pass condenser C4 and the high tension source AR which is connected to the terminals FCT is also shunted by a suitable 'oy-pass :ondenser of Figure 1 fir-2. i. ein parallel with thecorr- 65 denser Cl (not shown in Figure 3) across which (in each of the two embodiments of Figures 1 and 2) the uni-directional potential is to be applied. Pl is a potentiometer whereby the modulation input to the valve AA may be adjusted.

Although the invention has been specifically described as applied tocircuits `,wherein there is only oe tube to which modulating and carrier potentials are applied the invention is not limited to such applications and may be applied, with comparatively minor circuit modifications necessitated by the change, to circuits employing a plurality of such tubes either in parallel or in push-pull.

What is claimed is:` A In a modulation system an electron discharge device having an anode, a cathode, a screen grid electrode, a grid electrode between said screen grid electrode and anode and a grid electrode between said screen grid electrode and cathode,

a source of modulating potentials, a `source of carrier wave energy to be' modulated, a circuit connecting said source of carrier wave energy to said cathode and to said grid electrode between said screen grid electrode and cathode, a resistance having one terminal connected to said anode and the other terminal connected to said cathode, means for impressing a direct current potential on said resistance, a connection between said screen grid electrode and a point on said resistance, means for impressing direct current potentials which vary substantially in accordance with the mean amplitude of the modulating potentials between the cathode and the grid electrode between said anode and screen grid electrode, and means for impressing modulating potentials from `said modulating potential source on the anodeof said tube and said cathode.

LESLIE TYRRELL MOODEY. CYRIL ROBERT STAINES.

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