US2136479A

US2136479A - Modulation system

Info

Publication number: US2136479A
Application number: US654605A
Authority: US
Inventors: Trevor Bertram
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1933-02-01
Filing date: 1933-02-01
Publication date: 1938-11-15
Anticipated expiration: 1955-11-15

Description

1953 2 Sheets-Sheet l www B. TREVOR MODULAT ION SYSTEM Filed Feb. l,

kmu @SE1 INVENTOR BERTRAM TREVOR 'l c o o o o Nov. 15, 1938.,

Nov, 15, 1938..

AMM/HH) 45 B. TREVOR MODULATI'ON SYSTEM Filed Feb. l,

2 sheets-sneek 2 INVENTOR BERTRAM TREVOR ATTORNEY'- Patented Nov.rl5, 1938 UNITED STATES PATENT OFFCE MODULATION SYSTEM of Delaware Application February 1, 1933, Serial No. 654,605

21 Claims.

The present invention relates to signalling systems and in particular to a novel method of and means for applying a wide band of modulating frequencies to a carrier wave and, in so doing,

5 altering a characteristic of the carrier wave in a manner truly representative of the signal modun lations throughout the entire band of modulating frequencies. The invention is applicable to practically the entire signal art, both radio and wired.

In a particular application of the invention, which will be used to illustrate the invention, the novel modulating system as of the present invention is used in transferring the modulation from a carrier of one frequency to a carrier of another frequency. Such a scheme may be used in relay systems where itis desired to convert an incoming signal modulated carrier to a carrier of a different frequency modulated truly representative of the signal in order that said carrier of the different frequency might be retransmitted, retranslated, or utilized in any manner. The incoming carrier may be a radio wave impressed `on a natural conducting medium or a carrier wave of any frequency impressed on a conducting medium. 'Ihe outgoing wave may be a radio wave impressed on a natural conducting medium or a carrier of any frequency impressed on a conducting medium.

The modulation system of the present invention is particularly eiiicient in operation and is well adapted to transfer a wide band of modulation frequencies with a minimum of distortion. Furthermore, in the present modulating scheme there is no change of percent modulation during the transfer of the signal from the modulated carrier of one frequency to the modulated carrier of another frequency.

In previous illustrations of this kind use has been made of Helsing modulation. This requires a coupling impedance of some kind common to the anode circuit of the modulator tube and the relay tube or power amplier in which the new carrier is to be modulated. With a wide band of modulation frequencies this coupling imped- 45 ance becomes complicated, expensive and difficult to shield. In systems as known heretofore the percent modulation of the new carrier is more or less indeterminate. In operation of systems known heretofore careful adjustment is required to give an undistorted transfer of the modulation frequencies from one carrier to the other. Even when the utmost care is exercised the modulation transfer is accompanied by distortion and inefficient operation.

In the method of modulation and the method Renewed January 3, 1937 of transferring one modulated carrier to a carrier of different frequency modulated by the signal of the present invention, no distortion or change of percent modulation can occur. The present system is simple in nature, efficient in operation, and, due to the simplicity 0f the equipment, which involves no complicated modulation coupling impedance, is lower in cost than systems known heretofore. Furthermore, in the present invention shielding of the modulating circuit, with its associated radio frequency circuits, is greatly simplified. This is particularly true with the transfer of wide band modulation.

In its simplest aspect the present method of, and system for, transferring the signal modulations from a carrier of one frequency to that of another involves the use of a high level radio frequency amplier, the input electrodes of which are energized by the signal modulated carrier to be transferred. The output electrodes of the radio frequency amplier deliver the signal modulated carrier to a linear rectifier. The linear rectifier feeds the demodulated signal from its output electrodes into the anode circuit of a second amplifier or a relay tube, the input electrodes of which are energized by the second carrier frequency. In this manner plate modulation of the new carrier by the signal modulations derived from the incoming carrier is accomplished. Any

linear rectifier may be used. Preferably a linear 5 diode rectifier is used. The 'direct plate current of the amplifier or relay, whose input electrodes are energized at the frequency of the new carrier, is the diode rectified current. Since this direct current is modulated with exactly the same percent modulation as the first carrier frequency, the power amplifier or relay tube is then modulated in its plate circuit exactly the same amount.

The basic circuit as described above may be modified by coupling the diode rectifiers to the screen gridcelectrodes in the amplifier of the new carrier frequency, or the diode rectier may be omitted by coupling the output of the modulated carrier amplifier directly to the anode circuit of the new carrier amplifier and producing modulation in the latter by selfrectication of the signal modulated carrier therein.

Many other novel features and advantages of the present invention will appear from the detailed description thereof which follows.

In describing the invention reference will be made to the drawings, in which:

Figure 1 shows a circuit including the modulating scheme of the present invention and the means for transferring modulations from one carrier to another;

Figure 2 shows a modification of Figure l; while,

Figure 3 shows a modification of Figure 1.

In the system disclosed, see Figure l, a source of signal modulated carrier MC feeds energy to a high level lcw frequency amplifier of the class B type at A. The amplifier A feeds energy from its output electrodes to a rectifier R. The output circuit of the rectifier R is in series with the anode to cathode circuit cf an amplifier PA to accomplish plate modulation therein. The input electrodes of the amplifier PA may be energized at high frequency from a source of high frequency oscillations O.

The high level, low frequency amplifier A of the class B type comprises a pair of electron tubes 2 and fl having their

control grids

8 and 8 connected to the terminals of an inductance i3 coupled with the inductance I2 connected with the source MC. The radio frequency input circuit may be tuned to the desired frequency by a variable capacity S. The control grids 6 and 8 are maintained at a potential to cause this stage to act as a class B amplifier by connecting said electrodes to the negative terminal of a biasing source, not shown, by way of a lead 1. The anode electrodes l@ and it are connected to the terminals of an inductance l5. The alternating current output circuit may be tuned to the desired frequency by a capacity i3. Direct current potential for the anodes I4 and I6 may be supplied by way of a lead from a source not shown. The stage A may be neutralized by connecting the anode ifi by way of a neutralizing capacity 28 to the grid 8 and the anode i8 by way of a second neutralizing capacity 2l to the grid 6. The amplified signal modulated carrier appearing in the inductance I5 is impressed therefrom on the inductance 23. The inductance 23 may be tuned to the desired frequency by a capacity 24. The rectifier comprises a pair of

diodes

26 and 28 connected in full wave relation to the terminals of inductance 23. The cathcdes 25 of the diodes are supplied with heating current from a transformer T. The secondary winding 29 of the transformer T is of the special low capacity to ground type so that the capacity between the cathodes 25 and ground is small. The cathodes 25 of the rectifier are connected by radio frequency choke RFC to the electrical center of an inductance 30. The inductance 3D has its terminals connected, as shown, to the

anode electrodes

32 and 34 of a pair of

electron discharge amplifiers

35 and 38. The input electrodes 3l and 33 of the

amplifiers

38 and 38 are connected to the terminals of an inductance 31, which is in turn coupled to an inductance 38 connected with the output of the source of high frequency oscillations O. The inductances 30, 3l' and 38 may be tuned to the frequency of the oscillations from O by

capacities

39, 40 and 4l respectively.

The tubes 3'6 and 38 and their circuits may be balanced by the neutralizing

capacities

42 and 43 connected as shown. The cathodes of the

tubes

36 and 38 are connected to ground, as is the electrical center of the winding 23. This completes a direct current circuit which includes in series the anode to cathode impedances of the

tubes

35 and 38, ground, and the anode to cathode impedances of the diode rectiiiers.

The anode electrodes of the

tubes

36 and 38 swing in potential in accordance with the moduandere lating currents representative of the modulations on the carrier current oscillations which fiow in the outpu't circuit of the

diode rectiiiers

26 and 28.

In operation the input to the class B amplifier including the tubes 2 and 4 must be adjusted so that the rectifier current meter I indicates a current ow which is equal to the normal plate current, for modulated operation, of the high frequency power amplifier including the

tubes

36 and 38 with the same working under class C excitation. The cur-rent I is, as indicated above, modulated with the same percent as the incoming frequency from MC. This modulated direct current ows through the plate circuit of the

tubes

36 and 38 in the power amplifier, accomplishing therein the same percent modulation as the high frequency carrier. The special low capacity to ground filament winding 29 for the diodes 2'6 and 28 should be supplied if a wide band of modulation frequencies is used in the signalling system.

The present system as disclosed is particularly well adapted to wide band modulation since the load impedance presented to the diodes in R by the high frequency power amplifiers in PA is almost a pure resistance having a value high enough to give linear detection and low enough to be able to obtain modulation over a wide band of frequencies, taking into account the capacity of the diodes filament winding and the input capacity of the

tubes

36 and 38 in the power ampliiier. The choke RFC must series tune with the input capacity of the power amplifier, that is, the modulation frequency input capacity, above the modulation band to be passed to prevent the diode rectiiiers from Working into a short circuit at any frequency in the band pass. This gives a rising high modulation frequency characteristic.

Improved operation may be had in some cases by adding a series tuned circuit LC, as shown in Figure 3, to tune to the low carrier frequency. This makes the diode rectiiiers work into a short circuit for the low carrier frequency, giving more efficient rectification. With this arrangement the choke RFC may be made the correct size to tune with the input capacity of the power amplifier just above the modulation pass band to give a rising high modulation frequency characteristic. If the rising high frequency characteristic is not needed, the RFC may be made l to series tune with the power amplifier input capacity at the low carrier frequency to have the diodes work into a short circuit at this frequency. In this case the LC series circuit need not be used. Also, the LC circuit may be used without the RFC to give more emcient rectification without obtaining a rising high modulation frequency characteristic.

Best results are obtained by neutralizing the power amplifier to prevent distortion of the negative modulation.

The modulated carrier frequency appearing in the output circuit of

tubes

36 and 38 may be coupled by way of an inductance 44 to amplifiers or directly to an antenna 48, or other load circuit, or to said antenna or load circuit by way of further amplifiers, etc., included in the unit 45.

The circuit disclosed in Figure l may be modified by causing the anode circuit of the power amplifier to act as a self rectier and include bcth the high and low frequency tuned circuits, that the circuit tuned to the low frequency carrier and the parallel circuit tuned to the new carrier frequency, in the plate circuit of the power amplier tubes. inatethe diodes.

The modified system may take many forms. For example, it may be as illustrated in Figure 2, wherein the source of modulated carrier MC supplies energy, as in Figure l, to stage A, which includes a high level, low frequency amplifier of the class B type comprisinga pair of discharge tubes 2 and 4 connected, as described hereinbefore, to source MC. The anodes I4 and I6 of tubes 2 and 4 are connected to a circuit I3, I5, which is tuned to the frequency of the signal modulated low frequency carrier from MC. In this circuit, however, the diode rectifier is eliminated. The circuit I3, I is coupled directly to the output circuit of the

tubes

35 and 38 in the power amplifier PA. The inductance L2, connected` between the

anodes

32 and 34 of the

power amplifier tubes

36 and 38, is coupled to the inductance I5 in the output circuit of the stage A. The signal modulated carrier from MC is therefore amplified in A and impressed on the inductance L2. The inductance L2 and capacit-1,1' Cz, connected in parallel therewith, are tuned to the frequency of the low frequency carrier supplied from MC. An inductance Ls is connected between one terminal of the tuned circuit L2, C2 and the anode 32, while an inductance L4 is connected between the other terminal of the tuned circuit L2, C2 and the anode 34. The inductances La and L4 in series with the inductanee Lz are tuned by the variable capacity C3 to the frequency of the carrier oscillations supplied from O. The amplified signal modulated carrier from This system would eliml MC is rectified in the anode circuit of the power amplifier tubes 36 and 3l). The signal modulated carrier from A is applied to the anodes and 34 of

tubes

33 and 38 and rectifier therein. This. causes modulation of the high frequency carrier wavefrc-m O, tending to produce two sidebands on the high frequency carrier of frequency equal to the frequency of the carrier from O plus and minus the frequency of the carrier from A. Since the circuit L2, Cz, La. L4, C3 does not support these sidebands (because they are too far from the carrier) they are not transferred to the

output system

44, 45. The

circuit

44, 45

i should be designed so as not to accept the carrier wave from A with its modulation, since there is direct coupling between 44 and the output of the amplifiers A. This condition allows only the modulated high frequency carrier to be passed through the 4amplifier 45. The rectified current I in the anodes of 36, 38, referred to hereinbefore,

is broken up by the high frequency wave from O. This modulation or breaking up occurs at such a high frequency as compared with the frequency of the wave from A that proper operation of the system is not interfered with. This bro-ken up direct current I is substantially smoothed out by the circuit L2, C2, L3, L4, Ca. The signal modulated carrier is impressed from the output circuit of the power amplifier 'PA on to the inductance 44 connected, as in Figure l,

with a load either directly or by way of power amplifiers. limiters. etc.

Although I have used triode tubes to illustrate the invention, it will be understoodthat any type of tubes may be used. For example, the

tubes

35 and 38 may be of the screen grid type as shown in Figure 3. Where screen grid tubes are used neutralizing of the stage may not be necessary. Moreover, when screen grid tubes are used the rectified currents in the output of the diode rectiers may be applied to the screen grid electrodes Sg as shown in Figure 3 rather than to the anodes as shown in Figure 1. The function and operation of the arrangement of Figure 3 is sufficiently close to the function and operation of the arrangement of Figure l to eliminate the necessity of repeating said function and operation here in connection with Figure 3.

Having thus described my invention and the operation thereof, what I claim is:

l. A high frequency thermionic relay comprising, a pair of electron discharge tubes each having input electrodes and output electrodes, said input electrodes being adapted to be energized by high frequency oscillations, said output electrodes being connected in a compound circuit, one branch of which is tuned to the frequency of said high frequency oscillations, and means for modulating the high frequency oscillations relayed in said tubes including, a source of signal modulated carrier wave of a frequency different than the frequency of said first mentioned oscillations, a circuit coupling said last named source to said compound circuit, and means for tuning another branch of said compound circuit to the frequency of the signal modulated carrier.

2.- A high frequency oscillation relay comprising, an electron discharge tube having its input electrodes energized at high frequency and its output electrodes connected with a circuit having two branches, means for modulating the oscillations relayed therein comprising a circuit for applying signal modulated oscillations to the output circuit of said tube, and means for tuning one of said branches to the frequency at which the input electrodes of said tube are energized and the other branch to the frequency of said signal modulated oscillations.

3. A high frequency relay comprising, a pair of electron discharge tubes having their input electrodes and output electrodes connected in cross neutralized circuits, said input electrodes being adapted to be energized by high frequency oscillations, a compound output circuit connected between the output electrodes of said tubes, means for modulating the high frequency oscillations relayed in said tubes including, a circuit for applying signal modulated oscillations of a different frequency to said compound output circuit, means for tuning a portion of said output circuit to the frequency of said first named oscillations, and another porti-on of said output circuit to the frequency of. said signal modulated oscillations.

Il. Means for converting signal modulated oscillations of one frequency into signal modulated oscillations of another frequency and for maintaining the percent of modulation constant during said conversion comprising, an electron discharge tube amplifier having its input electrodes coupled to a source of signal modulated oscillations, a source of high frequency oscillations, a second electron discharge tube amplifier having its input electrodes coupled to said source of high frequency oscillations, an oscillation circuit connected between the output electrodes of said last named amplier, said oscillation circuit being tuned to the frequency of the oscillations from said source of high frequency oscillations, means for coupling the output circuits of said amplifiers to each other, and a translating device coupled to said oscillation circuit.

5. A high frequency thermionic relay comprising, a pair of electron discharge tubes having their input electrodes and output electrodes connected in cross neutralized circuits, said input electrodes being adapted to be energized by high series with the anode to cathode impedances of said first named tubes and its input electrodes connected with a source of modulating potentials.

6. An arrangement as recited in claim 5 in which the filament of said diode is heated by a low capacity to ground filament winding.

7. Means for converting signal modulated oscillations of one frequency into signal modulated oscillations of another frequency and for maintaining the percent of modulation constant during said conversion comprising an electrode discharge tube amplifier having its input electrodes coupled to a source of signal modulated oscillations, a diode rectifier, means for coupling the input electrodes of said diode rectifier to the output electrodes of said amplifier, a source of high frequency oscillations, a second ,electron discharge tube amplifier having its input electrodes coupled to said source of high frequency oscillations, a resonant circuit connected between the output electrodes of said last named tube amplifier, said resonant circuit being tuned to the frequency of the oscillations from said source of high frequency oscillations, means for connecting the anode to cathode impedance of said diode rectifier in series with the output electrodes of said second named tube amplifier, and a translating device coupled to said resonant circuit.

8. Means for converting signal modulated oscillations of one frequency into-signal modulated oscillations of another frequency and for maintaining the percent of modulation constant during said conversion comprising, an electron discharge tube amplifier having its input electrodes coupled to a source of signal modulated oscillations, a diode rectifier, means for coupling the input electrodes of said diode rectifier to the output electrodes of said tube amplifier, a source of high frequency oscillations, a second electron discharge tube amplifier having its input electrodes coupled to said source of high frequency oscillations, an oscillation circuit connected between the v output electrodes of said last named tube amplifier, said oscillation circuit being tuned to the frequency of the oscillations from said source of high frequency oscillations, a circuit for connecting the anode to cathode impedance of said diode rectifier in series with the output electrodes of said second named tube amplifier, means in said circuit to tune the same to a frequency above that of the signal modulations, and a translating device coupled to said oscillation circuit.

9. A device as claimed in claim '7 in which a circuit which is series resonant to the frequency of the signal modulated carrier is connected in parallel with the output electrodes of said diode rectifier.

l0. A signal relay device adapted to relay high frequency signal modulated oscillations and, in relaying said signal modulated oscillations, to convert the same into signal modulated oscillations of another frequency in which the percent modulation is the same as the percent modulation in the first named signal modulated oscillations comprising, a pair of electron discharge tubes having their input and output electrodes coupled in neuralized circuits, a tuned circuit including an inductance for coupling the input electrodes of said tubes to a source of signal modulated waves, a pair of diode rectifiers having their anodes connected to the opposite terminals of an inductance, means for coupling said inductance to the output circuit of said first named tube, a second pair of electron discharge tubes having their input and output electrodes coupled in neutralized circuits, an inductance connected between the input electrodes of said last named tubes, means for applying high frequency oscillations to said last named inductance, an inductance connected between the output electrodes of said last named pair of tubes, a choking inductance for connecting the electrical center of said last named inductance to the cathodes of said rectifiers, a connection between the cathodes of said last named pair of tubes and ground, and a connection between the anodes of said rectifiers and ground.

ll. A high frequency relay comprising, a pair of electron discharge tubes having input electrodes and output electrodes and an auxiliary electrode, said input electrodes being adapted to be energized by high frequency oscillations, and means for modulating the high frequency oscillations relayed in said tubes comprising, a diode rectifier of the full wave type having its cathode electrodes connected with the auxiliary electrodes of said first named relay tubes and its anode electrodes connected to ground and coupled with a source of signal carrying oscillations, and a circuit connected between the cathodes and anodes of said rectifier and tuned to the frequency of the signal carrying oscillations.

l2. Means for converting signal modulated oscillations of one frequency into signal modulated oscillations of another frequency and for maintaining the percent of modulation constant during said conversion comprising, an electron discharge tube amplifier having its input electrodes coupled to a source of signal modulated cscillations, a source of high frequency oscillations,

a second electron discharge tube amplifier of the screen grid type having its input electrodes coupled to said source of high frequency oscillations, an oscillation circuit tuned to the frequency of the oscillations of said last named source connected between the output electrodes of said last y named amplifier, a rectifier coupled to the output circuit of said first named amplier on the one hand and to the screen grid electrodes of said second named amplifier on the other hand and a circuit series tuned to the frequency of said relaying said signal modulated oscillations, to Aconvert the same into signal modulated oscillations of another frequency in which the percent modulation is the same as the percent modulation in the first named signal modulated oscillations comprising, a pair of electron discharge tubes having their input and output electrodes coupled in neutralized circuits, a tuned circuit including an inductance for coupling the input electrodes of said tubes to a source of carrier waves, an output circuit including a plurality of branches connected between the output electrodes of said tubes, an inductance in said output circuit, a second pair of electron discharge tubes having their input and output electrodes coupled in neutralized circuits, an inductance connected between the input electrodes of said last named tubes, means for applying signal modulated oscillations to said last named inductance, an inductance connected between the output electrodes of said last named pair of tubes, said inductance being coupled to the in-ductance in the output circuit of said first named pair of tubes, and means for tuning a portion of the output circuit of said first named pair of tubes to the frequency of the signal modulated oscillations andv another portion to the frequency of the oscillations to be modulated.

14. In a relay comprising, an electron discharge tube having its input electrodes energized by high frequency oscillations, an output circuit connected between the output electrodes of said tube, a source of signal modulated carrier frequency oscillations, a rectifier having input electrodes connected with said source of signal modulated carrier oscillations, a circuit connecting the output of said rectifier with the output circuit of said discharge tube, and a reactance in said last named circuit for tuning the output circuit of said rectifier to a frequency above the frequencyv of the signal modulations on said carrier frequency oscillations.

15. In a transmitting system for transmitting signals which cover a Wide frequency band, an auxiliary carrier wave modulated in accordance with potentials characteristic of signals which cover a wide frequency band, means for amplifying to a high level the auxiliary carrier so modulated, means for rectifying at high level the amplified modulated auxiliary carrier whereby potentials characteristic of the signals of said wide frequency band are reproduced at substantially increased strength, a source of high frequency carrier oscillations, an electron discharge tube having an anode, a cathode and a controlling electrode, means for impressing high frequency oscillations from said last named source on said controlling electrode, means for modulating the high frequency oscillations in accordance with the reproduced signals of increased strength, comprising a circuit connecting said rectifier to the anode and cathode of said tube to supply to said electrodes the necessary operating potentials, and means for transmitting the modulated high frequency carrier oscillations.

16. In a system for transmitting signalling potentials which cover a wide frequency band, which potentials have been used to modulate an auxiliary carrier, an amplifier of the electron discharge tube type having input electrodes excited by said modulated carrier, said amplifier having output electrodes, a source of oscillat-ory energy of high frequency, a second amplifier of the electron discharge tube type having input electrodes coupled to said last named source, said second amplifier having output electrodes, and a rectifier having input electrodes coupled to the output electrodes of said first named amplifier and having output electrodes connected in series with the output electrodes of said second named amplifier to supply to said output electrodes the necessary operating currents, said rectifier and connection between the same and said output electrode being of low capacity relative to ground t prevent short-circuiting of high frequency wave energy by the circuits coupling said amplifiers.

17. In a system for transmitting potentials characteristic of signals which cover a wide frequency band which signals have modulated an auxiliary carrier, an amplifier of the electron discharge tube type having input electrodes excited by said modulated auxiliary carrier, said amplier having output electrodes, a source of oscillatory energy of high frequency, a second amplifier of the electrode discharge tube type having input electrodes coupled to said source of high frequency energy, said second amplifier having output electrodes, a rectier of the electron discharge tube type having input electrodes including a cathode and output electrodes including said cathode, a heating circuit for said rectifier cathode, means coupling said rectifier input electrodes to the output electrodes of said first named amplifier and means coupling said rectifier output elec'- trodes and said cathode heating circuit to the output electrodes of said second named amplifier of the electron discharge tube type, said rectifier cathode heating circuit being of low capacity relative to ground to prevent short-circuiting of high frequency wave energy.

18. In means for converting oscillatory energy of one frequency on which signal modulations covering a wide frequency band have been impressed into signal modulated oscillatory energy of another and higher frequency and for main.- taining the percent of modulation substantially constant during said operation, an electron discharge tube amplifier having its 'input electrodes coupled to a source of oscillatory energy modulated in accordance with signal potentials covering a Wide frequency band, said electron discharge tube amplifier having output electrodes, a rectifier having an anode and a cathode, transformer means having low capacity to ground in a circuit for heating said cathode, a circuit coupling the anode of said rectifier to the' output electrodes of said discharge tube amplifier, a second electron discharge tube amplifier having input and output electrodes, a source of high frequency oscillatory energy coupled to the input electrodes of said second electron discharge tube amplifier, means coupling the output electrodes of said second electron discharge tube amplifier to the circuit for heating the cathode of said rectifier and means coupling the output electrodes of said second electron discharge tube amplifier to a utilization circuit.

19. In means for converting oscillatory energy of one frequency on which signal modulations covering a wide frequency band have been impressed into signal modulated oscillatory energy of another and higher frequency and for maintaining the percent of modulation substantially constant during said operation, an electron discharge tube amplifier having its input electrodes coupled to a source of oscillatory energy modulated in accordance with signal potentials covering a wide frequency band, said electron discharge tube amplifier having output electrodes, a rectifier having an anode and a cathode, circuit means having low capacity to ground for heating said cathode, a circuit coupling the anode of said rectifier to the output electrodes of said discharge tube amplifier, a second discharge tube amplifier having input and output electrodes, a source of high frequency oscillatory energy coupled to the input electrodes of said second tube and a radio frequency inductance in a circuit coupling the output electrodes of said second electron discharge tube amplifier to the cathode of said rectifier, said inductance series tuning said last named circuit to a frequency above the signal modulations.

20. In means for converting oscillatory energy of one frequency on which signalmodulations covering a wide frequency band have been impressed into signal modulated oscillatory energy of another and higher frequency and for maintaining the percent of modulation substantially constant during said operation, an electron discharge tube amplifier having its input electrodes coupled to a source of oscillatory energy modulated in accordance with signal potentials covering a Wide frequency band, said electron discharge tube amplifier having output electrodes, a rectifier having an .anode and a cathode, transformer means having low capacity to ground for heating said cathode, a circuit coupling the anode of said rectifier to the output electrodes of said electron discharge tube amplifier, a second electron discharge tube amplifier having input and output electrodes, a source of high frequency oscillatory energy coupled to the input electrodes of said second electron discharge tube amplifier and a circuit coupling the output electrodes of said second electron discharge tube amplifier to the cathode of said rectifier and to a utilization circuit, said last named coupling circuit including means for tuning a branch of the same to the frequency of said source of high frequency oscillations, the entire coupling circuit being tuned to a frequency above the frequency of the energy passed by said rectifier from the output of said first named electron discharge tube amplifier to said last named circuit so that said rectifier does not work into a short-circuit.

21. In means for converting oscillatory energy of one frequency on which signal modulations covering a wide frequency band have been impressed into signal modulated oscillatory energy of another and higher frequency and for maintaining the percent of modulation substantially constant during said operation, an electron discharge tube amplifier having its input electrodes coupled to a source of oscillatory energy modulated in accordance With signal potentials covering a Wide frequency band, said electron discharge tube amplifier having output electrodes, a rectifier having an anode and a cathode, transformer means having low capacity to ground for heating said cathode, a circuit coupling the anode of said rectifier to the output electrodes of said electron discharge tube amplifier, a second electron discharge tube amplifier having input and output electrodes, a source of high frequency oscillatory energy coupled to the input electrodes of said second electron discharge tube amplifier and a circuit coupling the output electrodes of said second electron discharge tube amplifier to the cathode of said rectifier and to a utilization circuit, said last named coupling circuit including a parallel portion tuned to the frequency of said source of high frequency oscillatory energy said last named circuit being also series tuned to a frequency above the frequency of the energy passed by said rectifier from the output of said rst named amplifier to said last named circuit whereby said rectifier Works into a circuit of considerable impedance to thereby increase its efficiency.

BER'I'RAM TREVOR.