US2074440A - Modulator - Google Patents

Description

March 23, 1937. L. USSELMAN 2,074,440

MODULATOR Filed March` 2l, 1931- jg() Ei al CARE/7 W4 VE 00 we C5 MHH #MPU/vf@ INVENTOR +Z G. L. USSELMAN BY /r j l /wl/OL/ ATTORNEY Patented Mar. 23, 1937 STATES M ODULATOR George Lindley Usselm an, Port Jefferson, N. Y.,

assigner to Radio Corporation of America, a corporation of Delaware Application March 21,

2 Claims.

This invention relates to modulators and especially to side band modulators of the electron discharge device type.

In order to produce side band energy from carrier energy and energy of a frequency other than the carrier energy while at the same time suppressing the carrier energy, it has been proposed to apply carrier energy to the grids of a pair of triodes cophasally and the other energy, usually 1o modulating energy, to the same grids in phase opposition. By virtue of the fact that the two sources of energy were coupled to the same electrodes, undesired interaction between them frequently took place.

It is an object of this invention to provide .a carrier suppression modulator wherein such interaction is effectively prevented. Briefly, to do so, according to my present invention, I use four element or screen grid tubes, or in other words, tubes having more than three electrodes for electron discharge devices, to like pairs of grids of which I apply either the modulating cr carrier energy in phase opposition and to the other grids I apply the carrier or modulating energy cophasally. In this manner the energy sources are kept separate and prevented from interacting upon one another.

While the carrier or energy of higher order of magnitude in frequency may be applied to either of the grids of the screen grid tubes, I prefer to apply it ccphasally to the screen grids of my improved carrier suppression modulator.

Sometimes it is desirable that a small amount of carrier energy be transmitted in addition to the side band energy. Accordingly, I provide an arrangement of electron discharge devices wherein carrier energy is only partially suppressed. More speciically, and one way of doing so, according to the invention disclosed in my U. S. application Serial #61,259 iiled January 29, 1936, which is a division of the present application, grids of screen grid tubes are polarized differently and carrier alternating energy supplied thereto. Other grids of the system are supplied with modulating energy. As a consequence, in the output circuit of the tube arrangement, side band energy and a certain amount of carrier energy will appear.

Other general objects of my present invention are to provide transmitting and receiving systems utilizing my improved side band or carrier suppression modulator.

While I have sought to define my invention in its broadest aspects in the appended claims, it may best be understood, however, both as to its 1931, Serial No. 524,247

structural organization and mode of operation by referring to the accompanying drawing, wherein,

Figure 1 is a wiring diagram of a transmitting system having a side band modulator therein comprising a pair of screen grid tubes to which carrier energy is applied to the screen grids cophasally and modulating energy to the usual grids or grids adjacent the cathodes in phase opposition.

Figures 2 and 3 illustrate other forms of my side band modulator wherein relatively low frequency energy is applied to the screen grids or grids adjacent the anodes of a pair of electron discharge devices and wherein relatively high frequency energy is applied to the usual grids or grids adjacent the cathodes.

Referring to Figure 1 of the accompanying. drawing, relatively low frequency modulating energy, which may be considered energy of one order of magnitude in frequency, from a suitable amplier 2 connected with source l is applied in phase opposition through the medium of transformer 4 to the usual grids 6 adjacent the cathodes 8 of electron discharge devices I0, of the screen grid type. To the screen grids I2 of the grids adjacent to the anodes I4 of tubes ID, there is applied cophasally through conductors i6, I8 from a suitable source 20, carrier` potentials or energy which may be considered energy of a different order of magnitude in frequency relative to energy from source 2.

By virtue of the application to the grids of electron discharge devices lll of energy of difierent frequencies, there will appear in the output circuit 22 coupled to the devices, energy of frequencies equal to the sum and difference of the frequencies from sources 2 and 25J. Energy of carrier frequency will not appear in the output circuit 22 for the reason that the carrier energy is applied cophasally to the grids l2 and the carrier components appearing in the output circuit 22 eiectively self cancel one another by virtue of the pushpull arrangement of tubes IIJ.

For successful operation, the power supply source for biasing the grids and especially the screen grids, should be very constant for otherwise a large regulation in biasing voltages on the grids would cause modulation of the carrier at frequencies corresponding to the regulation. For the same reason the regulation of the high frequency generator which supplies the carrier voltage to the screen grids, should be constant to prevent extraneous modulation.

Inasmuch as the carrier and modulating energies are applied to diierent electrodes, they are, of course, effectually separated and cannot interact upon one another for the interelectrode capacity coupling the two sources together is so small that the two sources can be 5 considered for all practical purposes electrically separated.

y 1 Output energy from output circuit 22 may be "fed, if desired, to a filter 24 and one side band allowed to pass into an additional power am- 10 plier or both included in frequency multiplier 26 if. found necessary. The amplified energy from amplifier 2t may then be radiated or electromagnetically propagated by the action of antenna 28.

l5 If desired, the side band modulator of Figure 1 may be replaced by the scheme shown in Figure 2 wherein carrier energy from source 2D is fed cophasally to the usual grids or grids adjacent the cathodes of tube I0; whereas the modulating 2o energy is fed in phase opposition to the screen grid of electron discharge devices I0. The output circuit 3l) may be given a characteristic suiciently broad to pass both side bands generated or preferably, it is proportioned so as to 5 pass either the upper or lower side bands produced as found desirable.

Rather than apply, as shown in Figure 2, the high frequency energy to the grids adjacent the cathodes, the high frequency energy may be 0 applied to those ygrids as shown in Figure 3 in 4() sistance 5.

Consequently, depending upon the amount of current drawn by the modulating means I, 2, the voltage across resistance 5 will vary thereby varying the potential applied to the screen grids of 45 electron discharge devices lll.

High frequency currents may be prevented from flowing through the modulating equipment by the use of a suitable choke 'l and high frequency bypass condenser 9.

5f) The output of pushpull connected screen grid tubes l may be taken from the output circuit 30 and fed to a suitable amplifier il which may include, if found desirable, a frequency multiplier and the output of amplifier Il may be 55 further transmitted by means of a radiating antenna 28.

It should be clearly understood, that a similar arrangement may be used wherein the voltage on the grids adjacent the cathodes is varied in ac- 60 cordance with signal potentials by an arrangement similar to that shown in Figure 3. In that event, the cathode and anode connections to the source 3 would be reversed so that a suitable biasing potential is applied to the usual grids. To the screen grids of such an arrangement high frequency energy would be applied cophasally as shown in Figure 1.

It is obvious that various minor changes will readily suggest themselves to those skilled in the art. Consequently, my invention is not to be limited to the modifications described, but solely by the scope of the claims which I have appended hereto.

Having thus described my invention, what I claim is:

1. Means for modulating electrical waves derived from a source of undulatory energy by means of electrical waves of another frequency from a signal source and for substantially suppressing energy of a frequency equal to the frequency of one of said waves in the energy resulting from the modulation comprising, a pair of thermionic tubes, each having a cathode, an anode, a control grid electrode, and a screen grid electrode, a resistance and a source of potential in series connected to said screen grid electrodes for maintaining said screen grid electrodes at a positive potential with respect to said cathodes, a circuit for applying oscillations from one of said sources to the terminals of said series resistance and source, a second circuit for applying electrical waves from the other of said sources in phase opposition to the control grid electrodes in said tubes, and an output circuit connecting said anodes in push-pull relation.

2. In a signaling system, a source of undulatory wave energy of a predetermined frequency, a second source of wave energy of a different frequency, means for modulating the energy from one of said sources in accordance with the energy .3.)

from the other of said sources and for preventing reaction between said sources and for substantially suppressing energy of a frequency equal to the frequency of one of said sources in the energy resulting from the modulation comprising, a pair of thermionic tubes eaclr having an electron emitting cathode, an anode and a pair of grid-like electrodes, the grid-like electrodes of each tube being similarly disposed with respect to the other electrodes of said tubes, an impedance and a source of direct current potential in series connected between a grid-like electrode and the cathode in each of said tubes, means connecting one of said sources of wave energy across said series connected impedance and source of direct current potential for applying waves from said one of said sources substantially cophasally to corresponding grid-like electrodes in each of said tubes, a second circuit electrically separate from said last named circuit connecting the remaining grid-like electrode of each of said tubes in push-pull relation, said last named circuit being also connected to the cathodes of said tubes for applying electrical waves from the other of said sources in phase opposition to said remaining grid-like electrodes, and an output circuit connecting the anodes of said tubes in push-pull relation.

GEORGE LINDLEY USSELMAN.

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