US1760871A - Method of and means for preventing radiation and extra reradiation in radioreceivers - Google Patents

Description

June 3, 1930. BALLANTlNE I 1,760,871

METHOD OF AND MEANS FOR PREVENTING RADIATION AND EXTRA RERADIATION IN RADIORECEIVERS. Y

Filed June 17, 1924 2 Sheets-Sheet 1 Ll FF/(L571.

1 z I a ya June 3,- 1930. -s. BALLANTINE 1,760,871

METHOD OF AND MEANS FOR PREVENTING RADIATION v AND EXTRA RERADI'ATION IN RADIOREGEIVERS Filed June .17, 1924 2 Sheets-Sheet 2 a {|I|||||||| *t J- L5. A 4 7-63 3 ml "2-- c c017 Aa/am v 7; & Mu'd/rach'om/ a v Mn Jupmrvdyno mow I i v 1:): Q glwue'ntot; MW I A %A :-8 L L 6,2 al bi new;

the reradiation less perhaps by a ever, by the method of this'invention.

Patented lune 1 930 UN- ITED STATES PATENT OFFICE;

STUART BALLANTINE, OE MOUNTAIN LAKES, JERSEY, ASSIGNOB OF ONE-Em TO RADIO FREQUENCY LABORATORIES, INCORPORATED, OF BOONTON, NEW JERSEY,

a conrona'rron or NEW JERSEY METHOD OF AND FORIPBEV'ENTING RADIATION AND EXTRA BADIOBEQEIVEBS nals. In theforme'r case the regeneration is used to amplify the signal; in the latter case the regeneration 1s pushed to the point of oscillation and the signal is rendered audible by the heterodyne beating of the local'and signal oscillations. The latter action is employed also in the so-called superheterodyne method of reception in which the signal irequency is lowered previous to amplification. In the present practice the regenerative or oscillatory elements of the receiver affect-the current in the antenna and cause either radiation or extra reradiation. Radiation is caused when the local-generation of energy is quite independent of the incoming signal. An example of this is a regenerative receiver which is allowed to oscillate. Extra reradiation is due to the regenerative efiect in the antenna,

and is distinguished. from normal rel-adiation. The normal reradiation is the-natural reflection from the antenna system, no regeneration being present. It is equal to the square of the antenna current multiplied by resistance. When regeneration is present the antenna current is increased or decreasedfirom its normal value and the reradiation is changed from its normal amount ;-the difierence is calledthe extraj reradiation in this'discussion.

Whileall reradiation aflectsanother neighboring antenna structure and receiver and may become undesirable, yet the normal reradiation cannot very well be eliminated unspeciallyfrequency independentregenerative increase of antenna resistance or try of the antenna. Both the extra reradiation may be eliminated, how- Such an object is very desirable, since radiation can interfere with the proper reception 0 signals at other nearby stations. With the present-day congestion of radio receivers, re-

0 radiating receivers are a very general nuiis to provide will be apparent from the by actually a terin'g the geonrethe radiation and audion repeater element A .Aprlicafionrleaiune 17, 1924.1. 720,708. I

s'ance, especially 'in connection with radio telephone reception. 7

As the regeneration can point of oscillation, both the regenerative and the oscillatory elements self-oscillation but for convenience of description the simpler expression oscillatory elemen will be used inthe following specificat-ion and claims tive as well as true oscillatory elements such as are purposely employed in heterodyne reception.

-' An object ofthe invention is to provide a radio receiver in which the'amplification of be forced' to the- I of receiving sets can be defined as -elemcntscapable of sustained in reference to regenera-' BEBADIATION. IN

the current or generation of other currents in the antenna or other collecting device by an oscillatory element is eliminated. object a radio receiver including an oscillatory element, but which will not cause undesirable extra reradiation. A further object of the invention is to pro 'de a radio receiver in which a substantially perfectly oneway repeater element is located between the Y current collecting element. More specifically an object of the invention is to provide a substantially perfectly one-way audion repeater.

These and other objects of the invention following specification when considered in connection with the accompanying drawings, in which Fig. 1 is a diagram showing the schematic organization ofth'e invention;

Fig. 2 is acircuit diagram showing an means and an oscillatory audionrepeater element with arrangements for-rendering it unidirectional, the effects of capacity coupling being eliminated by a cornpensation method;

Fig. 3 is a circuit diagram of a modifica tion of the circuit of Fig. 2y

Fig. 4 is a circuit diagram showing an audion repeater element with arrangements for rendering it unidirectional, a capacity coupl ngbeing Fig. 5 is a circuit diagram'showing an with arrangements eliminated by an f alternative compensation method;

ion

capacity coupling being eliminated by a neutralization method;

Fig. 6 is a circuit diagram showing an audion repeater element with arrangements for rendering it unidirectional, the effects of capacity coupling being eliminated by a modified Hazeltine neutralization method.

Fig. 7 is a circuit diagram showing the re.- lation. of the unidirectional repeater element of the type of Fig. 2 to an antenna and regenerative receiver of conventional type.

Fig. 8 is a circuit diagram showing the uni-' directional repeater element of the type of Fig. 2 used with a coil antenna and superheterodyne receiver of conventional type.

I shall now proceed to describe my invention with reference to a number of specific embodiments, giving, for the sake of a clear disclosure, definite constants and relations. I wish it to be distinctly understood, however, that my invention is in no way limited to the specific embodiments hereiii recited or to Cir-- cuit constants or other values here given;

The fundamental organization of the in- Theantenha is brought to resonance with the signal tdbe received y means of theantenna tuning ap aratus 1. The tuning network is designed to furnish to the input terminals of the unidirectional repeater 2 a high voltage and small current. Thisis amplified by the repeater and passed on, through suitable coupling impedanccs, to the receiving apparatus 3. The receiver contains oscillatory elements which will in general cause large currents to flow in the plate circuit of the umdirectional the device be unidirectional. By the term uni-w repeater. For the success of the invention it is necessary that these currents be prevented from establish ng any difference of potential across the input terminals, in other words, that directiona repeater or unidirectional audion stageas herein used, I mean a repeater or andion. stage which while perating over a predeterm ned frequency range will transmit impressed oscillations in one'direction, but will not to any appreciable e ent transmit oscillations inthe reverse direction. If this repeater is of the audion type and properly designed to F it not only attains the'ob'ject of the invention butfserves as a stage of amplification as well I and is of-two-fold utility. The'audion repeater element is rendered perfectly unidiree-j tional by providing isilpecial means -for eliminating the efiect of e current in theplate circuit upon the grid circuit, to which the antenna is connected. (In this discussion the term antenna is used generically to denote the collecting means, of whatever form.) An

ordinary audion repeater will not do on account of several actions which will be explained presently.

these is the capacity the capacit V trodes of coupli engendered by between the:gri and plate elece audion, and between the Wires between the coils or current through the The most important of and apparatus connected to these electrodes. The extra-audion capacity can be largely eliminated by shielding, as is well known to those skilled in the art; the efiects of the intro- I due to the capacity between grid and plateelectrodesof the audion and their connections;

2. On account of the flow of ions or electrons from the filament to the grid of the 3; On account of the coupling due to the flow. of the plate (thermionic) current throu h the filament; vention is shown schematically in Fig. 1.' 4. 5

maccount of the charge induced upon the grid charge 5. On account of condensers and their connections on either side of the repeater tube.

he, capacity coupling is compensated or neutralized by the general methods disclosed in my copending application or by the specific methods disclosed in the patent to Rice N 0. 1,334,118, 'or the patents to Hazeltine Nos. 1,450,080 and 1,489,228.

The coupling due, to the effect of the varying plate voltage upon any thermionic current that may be. flowing from filament to grid may be eliminated by biasing the grid and otherwise choosing the normal electrode voltages so that the smallest possible grid curelectrode by the varying, space any incidental coupling rent flows in the range of grid voltage impressed-upon the device. This is sometimes .accomplis edby connecting the grid return to the negative terminal of the filament; in other cases it may benecessary to insert a csfln y I I The efiectupon the grid circuit of the plate filament arises from the to resistance of the filament and is of importance only in the case of tubes having high resistance filaments. Examples of this are the audions lmown to the trade as Type [TV-201A, which have filament resistances between terminals of the order of 20 ohms. If

the plate return connects to one filament terminal the alternat' plate current flowin through the filament will cause the potential of every other. part of the filament, with respect to this terminal, to vary, with the result that a varying charge is induced u on the grid. I pro to this e ect y allowing the b tern I constituent of the plate current to enter t at both terminalsl This may be accom lished by shunting the filament terminals y a large condenser, the impedance of this condenser to the currents to be amplified being very small compared with the resistance of the filament and of the A batter and its connections 'A capacity of theord er of one microfarad is indicated at a frequency of one million cycles (300 meter wave length).

The effect of the varying space charge upon the charge induced upon the grid electrode resembles that due to the grid-plate capacity of the audion. The latter capacity coupling is due to the induction upon the grid of a charge by the varying plate charge. When the audion filamentis not heated this is the only coupling of this kind which exists.

When the tube is lighted, however, part of the electric flux from the plate is deflected to the electrons or space charge with the result that the efi'ective grid-plate capacity is changed. The general method of balancing,

3 either by compensation or neutralization, de-

scribed in my copending application may be used to eliminate this effect. A resistance component may sometimes appear, in which ;case a'perfect frequency-independent bal ance can be obtained. only by adding extra resistance in the compensatingor neutralizmg network.

The lncidental couplings, of electromag netic, electrostatic or other types, between the apparatus and connecting wlres external to the audion may be eliminated'by judicious shielding, as is well known to those skilled in the art. Since such shielding is general practice it'cannot beconsidered part of this in vention and is therefore omitted from the diagrams. The coupling between coils can usually be eliminated by a proper geometric arrangement, or by surrounding the coils by a copper shield of sutficient thickness. The

proper thickness will be determined by the' extinction coeflicient of the metal and the frequency; for example, a thickness of 0.015"

would be indicated for copper orsilver at, 300 meters. r

Thesemethods of rendering the repeater unit completely unidirectional are illustrated in Figs, 2, 3, 4, 5 and 6. The variety of these arrangements-is due tothe different methods of eliminating the elfective capacity coupling. i a.

Fig. 2 represents a repeater element suitable for interposition between an antenna and later oscillatory element. I The method of compensating capacity coupling .descrlbed in my oopending'application,Serial Number 629,702, and shown in Fig. 4 thereof, is used here. Figs. 2 and 3 differ in the.

method of forming the compensating winding. The reference symbols are uniform so that the following escription applies to both circuits. L and L constitute the input transformer tuned by means of the variable tain cases.

rangement may be made. The A, B and C' a batteries have their conventional locations. As described in the copending application just cited, capacity compensation is obtained by bringing point Y to the potential of'the point X. Point Y is the lower terminal of the input circuit, that is, the terminal having thelower alternating current potential, or, in general, most closely approaching to the alternating current potential of the filament. v This might have been done'by directly connecting X and Y but an insulating condenser would then have been necessary to keep the plate battery voltage 011 the grid. For this and other reasons .the inductive method shown is to be preferred, since it brings Y to the direct current potential of I the filament electrode. The output trans--"' 1 85 former is formed by L, and L which are,

tuned by C In Fig.- 2 the compensation 1s obtained by an extra winding L in Fig. 3 part ofthe coil L is used for the same pur- .pos'e; This is an example of a case where 'ing condenser of low impedance,which serves to introdu e the alternating current plate current through both filament terminals. R is a resistance which may be used to control the filament current and incidentally serve in biasing the grid negatively. C. represents a compensating capacity, which may obviously reside between the electrodes of the audion or their connecting wires, or in an external condenser. In certain cases it is desirable to add compensating resistan es R, and R to either C... or G, or both. either in series. as shown in Fig. 2, or in parallel, Fig.

3. The introduction of such resistance or other "balancing elements is in accordance with the principles of my conending application. I include them in these diagrams for generality; they may be omitted in cer- Fig 4 represents a repeater unit suitable for interposition between an antenna and later oscillatory element, specifically a regenerative element. A modification of the method of compensating the audion capacity coupling, described by Rice in Patent No.

1,334,118 is used. This modification consists among other things in the provision in. the

plate circuit. of an extra inductance, L,, f

cuit operative. In one specific experimental -whose function is to prevent the circuit from arrangement with L L =200 mchs, oscillations were obtained in a range of plate circuit inductance extending from 60 mchs. to

devised, for example, I may use a condenser shunted by a high impedance choke-coil, the choke-coil serving to .pass the steady normal plate current around the condenser. Special design of the transformer L L will often accomplish the same result. Referring to the diagram in this 'specific example, L and L ..are two inductors or parts of the same inductor; C2 is a variable condenser for tuning; C is a compensating condenser whose capacity is of the order of 10' microfarads;

is a compensating resistance of the order of 10 ohms; 'A is the filament battery; B the plate battery and C is the'battery used to bias the grid negatively to prevent the flow of thermionic current to the grid electrode; C1 is a filament shunting condenser of low impedance; L L is the output transformer. The functions of all these parts have already been explained. Theparticular values of these constants aremerely illustrative, and my inv'entionis of course not limited thereto. 4

Fig. 5 illustrates a repeater unit in which the audion capacity coupling is eliminated by a neutralization method. The principle of such methods is disclosed in my copend- -ing application. Referring to the figure, L

and L constitute. the input transformer which is tuned by the condenser C C 1s a compensating condenser; L and L are either separate coils or parts of the same 'coil; L and C3 represent the output circuit;

R 18 a compensating resistance; R is a resistance in the filament circuit, the direct current drop across which is used to give the grid a suitable negative bias; the C battery reinforces the biasing efi'ect of R; the A and B batteries have their conventional circuit locations; C is a filamentshunting condenser of low impedance. The

output circuit, represented by the coil L must be coupled to L and L so that the effective'impedances between the terminals of L and L are' of proper value to maintain a' state of balance in the circuit; obviously also the coupling between L L and L must be fixed. It is not necessary that L and L be coupled together, but their couphngs to L must result in impedances between their terminals which satisfy the requirements of neutralization. For best results with tubes of the usual 15,000 ohms plate resistance the coils L and L, are of small inductance com pared with that'of L and the coupling between L anad L and between L and L, should be close. In order that persons skilled in the art may reproduce my results, I give the following constants of one specific circuit; L =20 microhenries; L =20 microhenries; L 300 microhenries G 0.00033 microfarads 200 weoo meters.

Fig. .6 illustrates a repeater unit in'which an alternative method of neutralizing the audion capacity coupling is employed. The other arrangements for eliminating the enumerated couplings other than that due to the audion capacity are those already described. L and L are two coils of preferably tight couplings wound in opposite directions and so 4 connected that their noncommon terminal voltages are; opposite in phase; C is a compensating condenser; R

and R are compensating resistances, which 1 makeup the departure of the voltages of L and L from exact 180 phase relationship and which also compensate for the resist anace component of the variable space charge coupling; R is a filament resistance, the drop C =0.000005' microfarads. 1 .These values were found suitable for a unit designed to cover a wave length range of will be included as the proper design' of 7 this element is desirable for the eflicient operation of the repeater. Since the output will usually be into the grid circuit of another audion, the problemis that of obtaining a maximum secondary voltage in the coupled circuit arrangement. Let L L be the primary and secondary inductances respectively, and C the secondary capacity. The coupling between L and L is preferably made unity, in which case the maximum voltage across the secondary will be obtained when the secondary condenser is tuned so that:

1 QQEaL (1 L L and C are under the control of the designer. L and C are essentially related by the resonance condition. Usually the amplifier unit will be required to operate over a bandof wave lengths, in which case to some extent by the variation of- R with L for a particular .coil construction. Once tailed circuit diagram of peater of the type ofFig. 2 connected in front former, which with the condenser 0 serves to i the compensating coil L pensating resistances.

.serves to reduce the L, has been decided upon the optimum L can be calculated from the relation:

R, is the effective secondary resistance; B is the primary resistance plus the internal plate resistance important to note that in the use contemplated in this invention, where the repeater element may he succeeded by element, the secondary resistance R be diminished from its normal value by regeneration, so that Formula (2) shows immediately that L should be made considerably lower than it would be in the case of a normal multistage amplifier. In many cases L may be advantageously reduced to a single -turn, or if tighter coupling is desired, a number of single'turns in par These mathematical conclusions can be directly applied to the design of the output transformer in such arrangements as Figs. 2, 3 and 6; in applying them to the arrange ment of Fig. 5, of the load current is carried by the coil L, of Fig. 5. The optimum primaryinductance is entirely contained in the coil L of Fig. 5. With this understanding the principles apply uniformly. i

Specific applications of the invention are shown in Figs. 7 and 8. Fig. 7 shows the dea unidirectional reof a regenerative receiver of conventional type. Anantenna'of ordinary elevated type is shown. The repeater'unit is so designed that from the point of view of the regenerative receiver its output circuit has electrical resemblance to an without special modification. Referring to Fig. 7, L and L represent the input transtime the antenna; C is a compensating condenser, which may be partly external to the audion or be replaced completely by the gridfilament audion capacity; C. is a. filament shuntingcondenser of low impedance, which with tubes having high filament resistances,

return current upon is an inductance to which or to part of: which may be 'ap ro'x1- condenser whose capacity is a mately that of an average antenna; battery used to tube 1 negatively, and R R are phase com- In the regenerative receiver,;L, and C, constitute the tuned input -)circuit'; regeneration is obtained by back-doupling through the tickler coil L as U.'- S. Patent-No. is the detector audion of the regenerative receiver,- 3 and 4 being audio amplifiers coupled through the audio transa regenerative the flow of electrons; obviously, the repeater circuits must be balanced with normal filament current it mustbe noticed that .none

antenna, so that the unit can be placed in frontof difierent receivers.

.plete extinction by efiect of the thermionic the grid potential; L

is coupled; G is a bias the grid-of the repeater.

grid

L as in present practice, the regenerative am-' plificatio n would change the current in the ofthe amplifier tube. It is could oscillate into the antenna and cause antenna and cause extra reradiation, or -it radiation. Both these possibilities areeliminated by the circuit of Fig. 7, because by the interpositon of a perfectly unidirectionthe action can be relayed from grid to plate, but tion. V

'I- have already. pointed out that the efiec-i tive grid-plate capacity of the audion is changed from its therefore,

the filament of the audio heated, with the flowing and normal electrode voltages impressed: A cold-tube balance will be spurious. In the circuit used in Fig. 7 and Fig. 2, where the grid-filament capacity of the audion is in the balancingarm of the bridge, the same remarks apply to the grid-filament capacity. This too .will be subject 'to change by the electronic current, and since its change will not in general exactly follow that of the grid-plate capacity, a .hot-tubebalance will be, required. Since these effects are new I will givethe following experimental data concerning them. The constants of one specific repeater circuit (Fig. 7) were as follows: L =25 microhenries, C ==O.00025 microfarads, L comprises 12 microhenries fitting overL. with air. space and located near ground .potential point of L Letting the regenerative receiver oscillate and listening on the antenna sidewith a two-stage amplifier, it possible to get comv point varies with the fiequency due to ca'. pacity unbalance between L,, and L4 variation of electronic component of'finterelectrode capacities. The value of C varies consistentlylwith the filament temperature; when filament is lit to full brilliancyC is from 5 to 9 microfarads less than for cold tube. I

Fi 8 shows a second embodiment. In this case ftnoil antenna is used, no input trans formerv being repeater is of the type of Fig. 4. A superheterodyne receiver of conventional type suc-' true geometrical value by a 4 C The balance and t6- necessary and the unilateral ceeds the-repeater. This is an example of a 1 true oscillatory. generative element,

I the potential of the filament and'batelement rather than a re;-

the object in this case being to prevfint the oscillation generatedlby the-local osci of this circuit is the same as that of the preceding one.

- While a true unidirectional repeater can be obtained only by correcting for each of the disturbing causes noted above, it is apparent that the amount of feed-back due to the Several causes will vary. with different tubes and to 'a smaller extent with the. circuit in which the tube is employed. 4 In some cases, therefore, a substantially. one-way repeater action can be obtained without correcting for .a disturbing influence which is ofa negligible value.

I claim: 1.'In a radio receiver, the combination with a current collecting deviceand an oscillatory element, of a unidirectionalrepeat- -er located between said current collecting device and said oscillatory element, said unidirectional repeater comprising the combi- .nation of an audion tube with means for reducing effects upon the input circuit termi- "'prisin in combination, means the e ects upon the lnput c1rcu1t termmals nals of variations in potential across the output circuit terminals due to the grid-plate capacity of saidtube, means for reducing the flow of current from the grid to the filament, means for reducing the. flow of alternating plate current through the filament, and means for reducing incidental couplingbetween elements in the input and output circuits of said tube.

2. A unidirectional audion reipeater comor reducing of variations in potential across the plate circuit load due to the grid-plate capacity of the audion tube and the effects of the charge induced upon the grid 'by varying space charge in the tube,-means for reducingthe effects of the flow of current from the grid ,to the filament, means for reducing the effects of the flow of plate current through-the filament, and means for reducing the effects of incidental coupling between elements in the input and output circuits of the tube.

3. A vacuum tube amplifier stage having an impedance network arranged in the form of an alternating current Wheatstone bridgeof which the input and output circuits of the stage form. conjugate arms, and of which one balancing arm comprises capacity between grid and plate, anda second balancing arm comprises a reactance and a phase circuit including an output transformer of adjusting resistance between grid and filament of the vacuum tube.

4. An electrical amplifier comprising a vacuum tube, an input circuit, and an output output transformer, the in'lpeda'nces between plateand filament of said vacuum tube, one terminal of said input circuit-being connected to the grid of said vacuum tube, and the other terminal of said input circuit being connected to a point in the secondary of said output transformer, the impedances between grid and plate and between grid and filament of said vacuum tube cooperating with saidoutput transformer to provide the four balancing arms of an alternating current Wheatstone bridge across which said input and output circuits are arranged as conjugate arms.

5. A unidirectional audion repeater comprising, in combination, means adapted to reduce effects upon the input circuit terminals of variations in potential across the output circuit terminals due to the grid-plate capacity of the audion tube, means adapted to reduce efiects' due to flow of current between grid and filament, means adapted to reduce flow of alternating plate current through the filament, and means adapted to reduce'efi'ects of incidental coupling between elements of the input andoutput circuits.

6. A unidirectional amplifier stage comprising a vacuum tube having a control grid, cathode and. plate; circuit elementsproviding an input and an output circuit forsaid loo stage, means for tuning one of said circuits to resonance at a desired frequency, means preventing the varying potential of said outputcircuit from acting through the gridplate coupling to establish variations of po- 5 tential across said input circuit, means establis hing a direct current potential between said control grid and cathode to prevent the flow of current between cathode and gridi means rendering the direct current potentia between said control grid and cathode substantially independent of the flowof space current through said cathode, and; means shielding the elements of said input and output circuits to reduce incidental couplings to and between the samef.

In testimony whereof, I alfix my signature.

STUART BALLANTINE.

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