US1760225A - Radio transmitter - Google Patents

Description

May 27, 1930. P, D, ZURIAN 1,760,225

RADIO TRANSMITTER Filed May 19, 1927 /9 32 95 'M I M I F 26 +1. I 4l/ 19 m f INVENTOR BY g, ATTORNEYS l atented May 27, 1930 cries.

21111.1? 1). ZURIAN, on MADISON", Wisconsin, lasers-non, BY MEsNn'AssIGnMENTs', r0 BURGESS BATTERY 00., or MADISON, WISCONSIN, A CDRPORATION on wis- CONSIN RADIO TRANSMI ITTEB Application filed May 19, 1927. Serial No. 192,520.

This invention has to do with vacuum tube signaling systemsespecially high frequency transmittersand relates more particularly to the conservation of the electrical energy supplied to vacuum tubes.

The specific embodiment of the invention described herein is a vacuum tube transmitter comprising a master-oscillator and poweramplifier, the former functioning to generate high frequency oscillations which may be of relatively small intensity and the latter functioning to amplify the oscillations produced by the master-oscillator before they are impressed upon the transmitting antenna.

The circuit arrangement to be described provides for complete and practically instantaneous stoppage of plate current both in the master-oscillator and power-amplifier except when signals are actually being transmitted, thereby effecting a large saving in current consumption. This is accomplished in a manner which is not only highly satisfactory from an operating standpoint, but one which results in simplicity of arrangement and an important saving of batteriesthe size of batteries required being reduced to a minimnm.

The principal feature of the invention as incorporated in the specific embodiment herein described, lies in a novel circuit arrangement whereby a high negative potential is normally applied to the grid of the poweramplifier tube, this potential being sutticient to completely stop the flow of plate-filamentcurrent in that'tube, and being supplied, in part, by the battery which furnishes plate current to the master-oscillator. This double use of one battery results in a very substantial saving in operating cost.

The accompanying drawing illustrates diagrammatically the vacuum tube transmitter comprisinga high frequency vacuum tube master-oscillator, designed to generate sustained oscillations and a vacuum tube poweramplifier which functions to amplify the oscillations generated by the master-oscillator and to impress the amplified oscillations upon a transmitting antenna. This general type of vacuum tube transmitter is widely used and has the important advantage that its output frequency will remain substantially constant in spite of certain external disturbances such as swaying of the transmitting antenna and the like. This is due to the fact that the power-amplifier tube is unilaterally conductive and will not transmit to the master-oscillator disturbances which may occur in the antenna system. On short wave work this is a very importantconsideration and particularly so in portable installations wherein the antenna constants are apt to fluctuate to a considerable extent.

In the diagram, the master-oscillator portion of the system is shown below the dotdash line XX, while the'power-amplifier and transmitting antenna are shown above that line.

The master-oscillator vacuum tube is indicated by reference numeral 1; the poweramplifier vacuum tube by reference numeral 2.

Vacuum tube 1 comprises a grid or control electrode 8, a plate 9 and a filament 10. The oscillator circuit is an adaptation of that described and claimed in United States Letters Patent, No. 1,585,244, granted to William H. Holfman, May 18th, 1926, and is designed with a View particularly to efficient short Wave transmission although itsutility is not limited in that respect. The oscillator circuit comprises a pair of inductance coils 5 and 6 which preferably are of substantially equal inductance,and four condensers 7, 13, 14 and 17. The latter is indicated as being variable and in combination with condensers 13 and 1s functions as a frequency determining capacity. Condenser 7 is a stopping condenser which functions to permit the passage of high frequency currents while preventing the flow of direct current. A high resistance 15 is connected at one of its terminals to a point 16 between condenser 7 and inductance coil 6 while the other terminal of the resistance 15 is connected to apoint between condensers l3 and 14C. Condenser 7, being of relatively large capacity, ofiers substantially no impedance to the high frequency current, and ac- 'cordingly the high frequency potential at point 16 is substantially the same as if that condenser were not present. The condensers 13 and 14 are preferably of equal capacity and for that reason the high frequency potential at their juncture is equal or substantially equal to that at point 16. That being the case, there is substantially no high frequency cur rent flow through resistance 15. The latter resistance functions a leakage path be tween grid and filament and its value may be of the order of 5000 to 20,000 ohms.

The extremities of coils 5 and 6 are con nected respectively to plate 9 and grid 8.

Plate current to the oscillator tube is supplied by a battery 24, the positive terminal of which is connected to the juncture between coil 5 and condenser 7 the high frequency potential of which point is substantially equal to that of point 12 to which the filament is connected. The negative pole of battery 24 is connected to terminal 26, from which the circuit extends to negative filament through a telegraph key or relay, the contact of which is normally open. From an examination of the diagram it will be seen that the high fre-' quency current cannot flow to any substantial extent from plate to filament through battery 24 because of the fact that the latter is connected across points of substantially equal high frequency potential.

The filaments of both vacuum tubes are connected in parallel and supplied with heating current from a battery 18, or other suitable sourceof current which also may be alternating in character. I

High frequency oscillatory exciting voltage generated by the master-oscillator is supplied to the grid 19 of the power-amplifier tube through conductor 20 and stopping condenser 21. The connection of conductor 20 to coil 6 is indicated as being variable. This permits an optimum value of exciting voltage being supplied to the power-amplifier tube.

The output or plate circuit of the power.- amplifier tube includes a source of current such as a plate battery 28, a parallel tuned circuit 29, 30 and an adjustable contact 31 by means of which a variable number of turns of thecoil 29 may be connected between the battery 28 and plate 23. Tuning of thepoweramplifier plate circuit is effected by means of variable condenser 30. A source of alternating current also may be substituted for plate battery 28.

For the purpose of preventing the poweramplifier from oscillating independently of the master-oscillator due to the internal gridplate capacity of the power-amplifier tube, a small variable neutralizing condenser 22 is provided. This is connected between plate 23 and coil 5 and serves to impress on plate 23 a fluctuating potential which is equal and opposite to that caused by the internal tube capacity.

The transmitting antenna is indicated by reference numeral 4 and includes a coil 3 which is inductively coupled with coil 29.

The high frequency energy to be radiated is thus impressed upon the antenna.

Where any substantial amount of energy is to be radiated the plate battery 28 is necessarily of considerable size and correspond ingly expensive. Therefore, it is very desirable, if not entirely essential, to avoid any useless or unnecessary drain on that battery.

pletely stop the flow of plate current in the power-amplifier tube, and the plate-filament circuit of the master-oscillator tube is at the same time held open.

A novel and outstanding feature of the arrangement lies in the utilization of master- 0 cillator plate battery 2-las a source of grid biasing potential for the power-amplifiertube and the arrangement of the keying .device or starting relay contact so that upon closure the negative potential on the grid of the power-amplifier tube reduced to the proper value for operation of that tube and at the same time, the master-oscillator plate circuit is closed. 7

Assuming the hey connected across terminals 2t and 27 to be open, batteries 24 and 25 are connected in series between plate 9 of the master-es *illator tube and grid 19 of the power-amplifier tube. lit will be noted teat with the key open there is no direct current connection from batteries 2% and 25 to filament, but, nevertheless, there is an effective negative potential impressed on grid 19, of sutlicient intensity to 'ompletely or substantialiy stop the flow of platecurrent' through the amplifier tube. ihis is believed to be due to tne charging up of the internal gridfilament capacity of the amplifier tubethis capacity being in series with the batteries 24: and 25. The result is that when the key is suddenly opened the grid 10 becomes highly negative with respect to filament.

Battery 2 is selected to give the proper plate voltage for the master-oscillator tube while battery 25 is selected with a view to providing the desired negative bias on grid 19 when the power-amplifier is in operation. At the same time the combined voltages of those two batteries should be sufficient to provide the necessary negative potential on grid 19 to stop the flow of current from curren 7 source 28 when the key is opened.

Upon the closure of the telegraph key or relay contact across terminals 26 and 27, the

negative terminal of battery 2% and the positive terminal of grid biasing battery are connected simultaneously to the negative filament terminal and the circuit is thereupon put into operation. The plate circuit of the master-oscillator being completed oscillations are generated and the negative bias on grid 19 being lowered to the operating value, plate current flows in the power-amplifier tube. The response to the opening and closing of the hey is without any apparent lag.

A radio frequency choke coil 82 is inserted in series with battery 25 to prevent passa e of high frequency current therethrough.

By way of example, a radio telegraph transmitt rctly in accordance with the circuit herein described has been constructed and successfully operated. The master-oscillator tube corresponding to tube 1 was of the receiving type commonly known by the des ignation UX-201A.

The power amplifier was a 7% watt tube (UX-2l0). Batteries 24:, 25 and 28 were all dry cell batteries, battery 24 being of 180 volts, battery 25 0t 22 volts, battery 28 of 500 volts. Condenser 21 had a capacity of approximately 0.0001 microtar-ads, condenser 7 of 0.005 microtarads, condenser 13 of 0.0005 microfarads, condenser i l of 0.0005 microtarads and condenser 17 had a maximum capacity of approximately 0.00005. The resistance element 15 had a value of approximately 20,000 ohms. The capacitance of condenser 22 was about 0.00005 microtarads maximum. Coils 5 and 6 each were 2% 01- ameter and consisted of 5 turns of 12 gage copper wire. Coil 29 was 2 diameter and consisted of approximately 7 turns of 12 gage copper wire. Coil 3 was 2 diameter and consistedoi 6 turns of 12 gage copper wire. Choke coil 32 was 1 in diameter and consisted of approximately 200 turns of 28 gage copper wire. The maximum capacity of variable condenser was about 0.00025 microtarads.

While this invention has been described only in its application to one particular type of transmitter, it will be evident that it may be applied with equal advantage to vacuum tube systems of other forms and to wire transmission systems as well as radio. Also it will be recognized that the application of this invention may be made with equal facility to either radio telegraphy or telephony.

What is claimed is:

1. In a vacuum tube transmitter, a masteroscillator comprising a vacuum tube, a platefilament circuit for said vacuum tube, a plate battery and circuit interrupting means in said plate-filament circuit, an amplifier comprising a vacuum tube, circuit connections b tween said master-oscillator and amplifier r supplying high frequency exciting volte to the latter, a plate circuit for said iplifier including a second source oi plate .rrent, a grid circuit for said amplifier inn w new. 0

eluding a grid biasing battery, the negative terminal o which is connected to the grid of said amplifier tube, said first mentioned plate battery and said grid biasingbattery bem connected in series a circult connec- D i u I 7 I u tron between the osltive terminal of said grid biasingbattery and the filament of at said vacuum tubes and ClI'CLlllJ least one oi interrupting means in said last mentioned circuit connection.

, 2. A hi h frequency transmitting system comprising a vacuum tube master-oscillator and a vacuum tube power-amplifier, said master-oscillator bein connected: to the input terminals of saidpower-amplifier and funcadapted to be connected to a filament terminal of one of said tubes and means for in terruptedly connecting said joint terminal to said filament terminal, the, combined voltage of said current sources being such as to impress a suificient negative bias on the grid of said power-amplifier tube substantially to prevent the flow of plate current through said tube. l

3. Ina high frequency wave signaling systerminal between said current sources being tom a vacuum tube oscillator, a power-amplifier comprising a vacuum tube, said poweramplifier being operatively connected to said oscillator and adapted to amplify the oscillations produced by said oscillator, a source of unidirectional current connected between the plate and filament of said powenamplifier for applying space current thereto, a current source connected between the grid of said power-amplifier and the plate of said oscillator whereby a negative potential is applied to the grid of said amplifier sufficient substantially to prevent any flow of current between the plate and filament of said power-amplifier, a part of the last men tioned current source being adapted to supply plate current to said oscillator, and switching means included in a direct-current circuit between the plate and filament ot-said oscillator, said last mentioned circuit including a part only of the current sourcebetween the plate of said oscillator and the grid ofsaid power-amplifier, said switching means being operative to reduce the negative potential on the grid of said power-amplifier and at the same time to close the-plate circuit of said oscillator thereby causing said oscillator to generate high frequency oscillations and simultaneously rendering said power-amplifier operative to amplify said oscillations.

4. The method of operating a vacuum tube high frequency transmitter comprising a vacuum tube master-oscillator and a vacuum tube power-amplifier which consists in normally applying a negative potential to the grid of said power-amplifier of such value as substantially to stop the flow of plate current through said amplifier, reducing the negative bias on the grid of said power-amplifier sufficiently to permit a flow of plate current therethrough and simultaneously closing the'plate circuit of said master-oscillator.

In testimony whereof I aflix my signature.

PHILIP D. ZURIAN

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