US1365576A - Radio-receiving syste - Google Patents

Description

W. C. WHITE'L mmoaacuvma SYSTEM.

APPLICATION FILED OCT. 1!. 1917.

1,365,576, Patented Jan. 11,1921.

Inventor William C. hite,

Grid Volt-a e by His Attorney.

, To all whom it may concern.

" UNITED-STATES rArsnrorrlcs.

WILLIAM 0.. warm, or sciasnncran'x, NEW YORK, assronoa '10 GENERAL ELEG- TRIO COMPANY, A conrona'rron or NEW YORK.

nanro-nncnrvmo sYsrrz'...

Specification 01' Letters Patent. Pate t d Ja 11 1 2 Application filed October 11, 1917. Serial No. 196,051

Be it known that I, WILLIAM Warm, a citizen of the United States, residlng at Schenectad in the county of Schenectady, j

State of ew York, .have invented certain new and useful Improvements in Radio-Receiving Systems, of which the following is a specification. r

My present invention relates to electron discharge devices, and more particularly to the construction of such devices and their use in radio receiving systems.

Electron discharge devices of the type comprising a cathode adapted to be heated to incandescence, a grid and an','anode inclosed in an evacuated envelop, have-been commonly employedin the past as detectors or receivers for radio signals 1n various ways. When these devices have been employed for the purpose mentioned it has been customary to use'a battery for heating the filamentand a second battery in a circuit between the cathode and anode for supplying current for operating the signal; indicating apparatus. With the construction of these devices which has generally been employed, it has been necessary to use a battery of twenty volts or more in the circuit between cathode and anode, which for convenience in description may be designated as the plate circuit. It has also been frequently desirable to employ another battery in the circuit between cathode and grid for adjusting the normal potential of the grid to a-value at which the device will operate most satisfactorily.

The object of my invention is to provide a device which may be used as a radio detector or receiver, as well as for other purposes in which a single battery of a few volts potential may be employed for fulfilling all of the functions carried out by the three batteries mentioned above. In carrying my invention into effect I construct theelectron discharge device in such a way that the cathode and grid are separated by as small a distance as possible without danger of their actually touching. each other, during the operation of the device and with the anode spaced from the grid bv a'distance which may be slightly greater than the spacing between cathode and grid .but which will in any case be very 'smalL- In using this device as a radiodetector I connect the anode directly to the positive terminal of the-battery which is employed for-heating the filament and include in this circuit only an indicating means such as a telephone receiver. Any adjustment of the grid potential which it is necessary to make may be brought about by connecting the gridto the positive or negative terminal of the filament or to some polnt of an 1ntermed1ate potential. In order that the device shall operate satisfactorily with the connectlon described, I find it preferable that the metal of which the anode is composed shall be electro-positive with respect to the cathode.

The novel features which I believe to be characteristic of my invention are pointed out with particularity in the appended clalms. The invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof will best be understood by reference to the following description taken n connection with the accompanying drawmg in which Figurel is an elevation partly broken away of a devlce whichmay be used in carrying myinvention into effect: Figs. 2 and 3 are diagrams illustrating two different circuit connections which may be employed in radio recelvlng systems, and Fig. 4 is a characterlstic curve of one of my devices. showing the relation between the voltage of the grid and the current in the plate circuit.

The device illustrated in Fig. 1 comprises an evacuated envelop 1, in which is inclosed a filamentary cathode 2, which is preferably of tungsten, a grid 3 which is in the form of a coil close to and surrounding the cathode and a cylindrical anode 4 close to and surrounding the grid 3. The anode 4 is preferably of a metal which is electropositive with respect to cathode 2, and I have found in practice that nickel is especially suitable for the construction of the anode. Current for heating the filament may be supplied through the leading-in wires 5 and leading-in wires 6 are connectedto the ends of the grid coil 3. Leading-in conductor 7 provides a connection to the anode. The .bulb 1 should be thoroughly baked out and exhausted to a vacuum as good as that ordinarily employed with vacuum lamps. During exhaustion current should be passed through the device to heat the anode in order to expel any impurities or oxids which there may be at or near the surface. This is of special importance as I haveiound that in order to obtain the most satisfactory operation the anode surface should be made as clean as possible. I find it convenient to make the grid 3 of tun sten and to use this as a cathode during ex austion. By this expedient sufficient current which may be of about six volts, or even less, furnishes heating current for the oathode 2, variable resistance 9 being inserted in series with this battery in order to ad ust the current through the cathode to the desired amount. The grid circuit of this devicecomprises the condenser 10, the usual inductance 11 and variable capacity 12 for tuning the circuit, the inductance 11 being coupled with the inductance 13 in clrcuit with the antenna 14. The anode 4 is connected to the positive terminal of battery 8 through the. usual telephone receiver 15. In practice I also usually find it most convenient to bring the grid connection to the positive terminal of the cathode 2.

It has been demonstrated that the operation of a device of this sort with the circuit arrangement shown depends upon the grad- 4 ual building up of a negative potential upon the grid by reason of the charging of the condenser 10 by successive radio frequency impulses received and the leakage of this charge during the interval between successive signals. In order for the device to operate most efiiciently it is desirable that the normal grid potential should be such that a small variation in its potential will produce a large variation in the current between the cathode and anode. In practice this relation may conveniently be expressed in terms of milliamperes change in plate current per volt change in grid potential. In Fig. 4 I have shown a curve which represents this relation in one of my devices, which is constructed in the manner described. It will be seen from an inspection of this curve that when no signals are being received, and the grid is therefore at substantially zero potential with respect to the cathode, the device will operate upon that portion of the curve which I is practically straight and which is also substantially the steepest portion. The maximum degree of amplification will also be obtained when operating upon this portion of the curve. If the normal grid potential is positive the current taken by the grid will be much greater than when the grid is at zero potential or negative, and as a result the changes in grid potential produced by the signals will not'be as great as when the potential of the grid time or negative. no extra. battery is necessai? in the grid oircuit to adjust the device or most eflicient operation. In order that the ne ative charge upon the grid which is accumu ated thereon during the receipt of a signal may leak ofi after the signal has been received and before the succeeding signal is impressed upon the grid circuit, it is desirable to employ a high resistance 16 shunting the condenser 10.

I have also found that in the operation of such a device in the manner indicated in Fig. 2 there is a tendenc for the grid to assume a negative potentia with respect to the cathode when no signals are being received, especially if the rid is connected to the negative terminal 0 the filament. To avoid this it is usually desirable to connect the grid to the positive-terminal of the filament as indicatedifin order that there may be at all times a slight leakage current between the grid and cathode. I

By the use of a cathode of'tungsten I am able to obtain an advantage over other forms of cathodes in that the cathode may safely be operated at a high enough temperature togive the electrons emitted an appreciable initial velocity. This initial velocity of the.

electrons will be great enou h to cause a current fiow between catho e and anode without any source of potential in the external circuit. By reason also of the fact that the material of the anode is electro positive with respect to that of the cathode there will be a greater flow of current between the two than there would be if both were of the same material. There will also usually be a sli ht drop of potential through the resistance% and this drop of potential will cause the anode to be slightly positive with respect to the most positive end of the It will therefore be evident that Y filament and thus assist the action of the device. It is evident of course that withthe connection shown the anode is positive with respect to the negative end of the cathode by an amount equal to the potential of the battery 8.

In Fig. 3 I have indicated a modification of my invention which is adapted to receive continuous wave signals by the heterodyne method. In this case the plate circuit of the electron discharge device includes an inductance 17 which is coupled with the coil 11 in such a way that local oscillations will be produced which are of slightly different frequency from the received oscillations and which will combine with the received oscildescribed may be operated asan oscillator claims.

to such a degree" that the energy which may be returned from the plate to the grid cire cuit is greater than the energy losses of the circuits, and previous devices of thistype have required a separate source of potential in the plate circuit to bring them to a point where their energy amplification would be great enough to produce oscillations.

7 While I have illustrated and described the preferred embodiments of my invention it is by no means limited to the precise con struction or circuit arrangement shown as many variations in the structural details as well as the manner in which'it is used may be made Without departing from the scope thereof as set forth in the appended What I claim as new and desire to secure by Letters Patent of the United States, is 2- 1. An electron discharge amplifying device comprising a metallic cathode adapted to be heated to incandescence, a grid and an anode inclosed in an evacuated receptaole, said anodebeing composed of a metal which is electro-positive with respect to the metal of the cathode and the parts being so proportioned and so close to each other that the maximum degree of amplification of which the device is capable may be ob- 'tained with the grid normally at substanplying current for heating the cathode and 'for the operation of the device as an am 'p'lifien- 2-. The combination in a "radio receiving system of an electron discharge device having a filamentary cathode of tungsten, a grid and an anode of nickelinclosed in an evacuated envelop, a single batteryof not over six volts for supplying current for heating the cathode and for operating signal indicating means, the two terminals of said battery being connected to theterminals of said cathode, means for impressing received signals upon said grid and a connection from the .anode to the positive terminal of said battery, said connection including signal indicating means.

3. An electron discharge device comprising a filamentary cathode of tungsten, a grid and a nickel anode inclosed in an evacuated receptacle, the parts being so proportioned and so close to one another that the device is capable of operating to produce oscillations from a direct current source of a potential as low as six volts. 4

In witness whereof, I have hereunto set my hand, this 10th day of October 1917. WILLIAM (J. WI IITE.

Images