US1627718A - Radiotelephony - Google Patents

Description

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Patented May 10, 1927.

raiser o ar es.

PAUL \VARE, OF YORK, 'N. Y., ASSIGNO-R 'IO WARE RADIO, INQ, OF NEW YORK, ,.N. lY.,-A GORPOEATION OF DELAWARE.

.RADIOTELEPHONY.

Application filed September 3, 1921. Serial No. 4%,339.

Thisfinvention relates to duplex or twoway radio com-mun-ication, more particularly to 'communication by telephone, wvherem communication can be had over considerable space, =wah0utmanipulation of switches or varying circuit conditions as between sending and receiving, in .azmanner similar to present day wire telephone communication.

The 3 invention employs at a station a power radiating element or antenna separate from' the element receiving incom ng oscillations, herein shown as a loop which i has *especial advantages in the system herein disclosed over an ordinary: antenna for receivingy-aswill be hereafter pointed out. T-he'objeets of the invention generally are to enable separate transmitting and I'GCelV- in}: elements to be 'installedwithin reasonable distance of eachother, as in the same building,without causing the receiving system to be paralyzed by the powerful transmitting system, while maintaining the necessary' sensitiveness to provide an efficient system wherein'power losses are reduced to a minimumyiand also to provide a system Which 'w-ill require no radio skill to operate and which" can be easily set up and used in outlying districts or where space is limited Without requiring a large fixed plant or ground area. Sue-ha system is herein provided wherein the transmitting element can be on the roof of a build-ing andi the receiving loop element either on thesame root, or within one of the rooms without' interfering one with the other and each stationbperated' by'automatically or manually controlled batteries andja dynamotor, the batteries being' chargeable whenthe system is notiin operation from any'suitable source: of power.

j-Sofar as'I am aware; there is nosystem as above outlined at present on the market er -available in the'art, notwitl-istanding that there is an enormous field't'or such'a-system either-"for telephoniccommunication in districts without any electrical communication at all -or"where present wiretelephones and telegraphs are more expensive or toowrestricted in operation,- or whereit is desired to extend thepresen't radius of coiunninication of wire telephones by radio. The circuits of this systemiare so arranged that they can be attached to ordinary wire telephone circuitspwhiclrhas heretofore been a r difiiculty in duplex radio extensions ofai'ire telephones.

In carrying out the invention, both the transmitting and receiving circuits are improved in various particulars, together with novelmeans confining the various currents to their own proper circuits, and for-shielding and protecting the receiving equipment from undesirable coupling with adjacent metallic objects such as pipes, frames of buildings, fixtures, etc, which might carry transmitter high frequency energy.

Any suitable source of; power maybeused for.transmitting, but as shown herewith, a storage battery and dynz-imotor, having suitablemeans for Qlllllll'lltlllgdtS ripple, are

provided. The transu'iitte'r includes master oscillator, power amplifier. and power zr'nodulator vacuum tubes, the circuit containing such tubes beingpreferably loosely coupled through an adjustable output transformer to the-transmitting element radiating continuous carrier wave oscillations. The telephone transmitter is adjacent the telephone receiver, as in wire telephony, and is connected in circuit with the primary of a modulation transformerwhosc secondary: is connected "withthe power modulator and remainder or the t'ansmitting'cireuit. .An importantieature of this transmitting-systenr' is that ibis-tree of operating adjustments, beingset once for all and operating without skilled attention under iinten'ded conditions.

Although an ordinary receiviim antenna may be used with such a transmitti-np system, a loop 'receii-"ing element has a number of advantages, especiallyior duplex operation. The improved loop "receiving;arrangementin conjunction with the transmitting high frequency circu'it localized auljacent, the antenna asdisclosed herein. has the additional advantage, 'ho'wever, of permitting much more closely situated sending: and receiving, equi 'nnentunder conditions encouu tered in practice than has heretofore been possible'to obtain. A preterre'd arrange-- ment is to 'localive the trznismitting high frequency equipment in a weather proof box at the antenna, as on the root of a building. The transmitting vacuum tubes should be in a separate ventilated but burglar proot compartment of this box. The loop receiver and its associated radio frequency circuits may also be out of doors, but it is of advantage to locate it indoors, especially if a storirejc battery is used to heat the receiving tube filaments and it is desired to locate this storage battery at the Jor-iition oi the transmitting storage lnatteiy. as herein provided, because it the rcce' p; circuit is locatx near the battery position there will be less power loss in the coiuiectiue; lines and. consequently a snuillcr battery is retpiired than otherwise.

By a novel. system of shielding: and the utiliaation of a loop of small size I am able to install the receiving set in an ordinary room without atl'ecting its sensitivcness or permitting it to he atlected by induction iron] the local transmitter. as through the frame (it the building, pipes, and other metallic objects. The receiving system. contains a. loop with its flat side approximately toward the antenna to pick up a. minimum of transmitter energy, and pointing: to the distant station and is preferably of the beterodyne type, as shown, wherein local oscillations derived from the transmitter. or preferably from a separate local oscillator. are of such difference in frequency from the voice modulated. incoming: oscillations as to produce a. voice modulated sip'i'ial beatiirequcncy. which is preferably out of andibihty frequency, this heat tl'requency being; amplitied by one or more amplifiers, and. finally demodulated or translated into the desirable voice frequencies in the telephone receiver.

l have "Found that a. small eloctrostatically shielded loop of-novel torm can be installed. in a room with the receiving tubes, transfin-rmn-s, etc, inside the, loop for compactness it desired, without being affected. by adjacent pipes, columns, gras meters, etc., with successful results, thus providing; a high frequency duplex telephonic communication system througl'i space, using' a desk telephone set automatically controlling the power unit from the desk set hook and completely eliminating all operating: adjustments, throw-over switches or the like.

The matter of eliicicncy is important in automatically controlled systems of this character, which must operate for considerable time without attention, because thus far only the smaller sizes of vacuum tubes have been developed to operate on reasonably low plate voltages that are satisfactory for this SGI'V'ICC.

In this system, the transmitting high frequency is isolated to the transmitting radiating system, eliminating the customary leadin wires, as on the roof, it the installation is made on and within a building, While a novel system of sheathed cables connecting the several units eilectively prevents inter- :t'erences.

The accompanying drawing shows a die.-

gram of a preferred form of? the invention, wherein-- Figure 1 shows a complete diagram of the invention, I 1

Figure 2 is a diagram of a suitable oppositely wound loop, and

Figure 3 shows the loop shield.

deterring to Figure 1, the upper part of the figure represents the transmitting unit, lelt hand lower part of the figure is the power unit, and the right. handlower part the receiving unit. The transmitter appa ratus is supplied with power ifrom a dyna motor and storage battery, which is charged from a suitable source of supply, andcontrolled by a main switch having one position for sending and receiving, and another for charging. I I I The power supply switches 37 and ill) (Fig.2. 1) may be manually operated, it desired, or automatically operated through holding relays coactingg; with the switches biased by gravity or spring means. to normally remain open. The holding relaysmay be controlled from a remote relay control switch 39 provided with a switch-hook, as suown. and so arranged. as to closcthe holdingrelay circuits when the receiver .78 is lifted from the hook, or to opensaidz circuits when the receiver is replaced thereon.- The antenna 1 is loosely coupled by output trans former 12 to the high frequency power circuit ol" tube 19. 1-1- the dynamotor with condensers 15, and its. output side supplies high voltage power to the master-oscillator 1S, amplifier 19 and modulator 20.. 21.. are condensers, 22 an ad ustable inductance :lor setting; the frequency, 23 -1s a coupling con.-

denser of proper capacity to drive thepower amplifier tube 19. and 24 is a blocking con denser. The modulation" system is aconstant currcnt one, wherein the sum ofthe currents to the modulator and amplifier tubes 20, 19, isconstant at voice frequencies. 25 is an adj ustable tuning-inductance to; tune the antenna to resonance as indicated by ammeter 26. l

Transformer 12, instead of functioning: like the usual oscillation transformer between :1 closed primary supply circuit and an antenna circuit, is similar to a power transformer Where the primary current drops very low on open circuit. This is effected by a high primary impedance at the band or range of operating frequencies when the secondary is detuned or open-circuitcd. thus protecting tube 19 from destruction, it the antenna breaks or becomes dctuned. In addition, the secondary fits loosely-overthe primary and the coupling is'finely adjustable. This avoids the use of taps on :the secondary to adjust the antenna load for maximum plate circuit efficiency in tube--19, regardless of antenna characteristics within reasonable limits. This avoids variation of etficiency in using taps, and can be set atthe time of installation to get the best output,

practice this is only necessary over quite long periods of time. A further advantage of the loose-coupled secondary is that in conjuno tion with themaster oscillator-power amplitier, circuit radio frequency chokes in the cable between. the transmitting unit and power unit, are not found to be necessary to confine the transmitter high frequency to the antenna circuit. It is very desirable, of course, to eliminate these-chokes especially those inseries with the filament lines because of the great power loss.

The positive terminal of the dynamotor 1% is connected to the plates of the tubes 19 and 20-through the voice'f'requency rcactance 28 by the wire l6-and to-the plate of tube 18 through the high frequency choke27 by the branch wire 29. 30'is a *nmdulation transformer having high resistance 31 across its secondaryto improve the modulation. The resistance 32 acts as a grid leak unit for independently regulating the grid-filament operatingpotentials of all three transmitting tubes-18, 19, 20 and obviating a separate battery to make the grids negative. The primary of transformer 30 is in series with battery 33 and telephone or other source'of speech 82. 34 is a resistance for regulating the filament currents of tubes 18, 19, 20 as supplied by batteries 36 connected to switchpoints 37. The leads 38 of battery 33 arelwistedas shown for apurpose hereafter to he described, and lead to switch points 39. The points 4-0, 41 are for charging all the batteries in series, when connected with the respecti-ve points 3T. 39 from suitable power source The switch points 39 close on points-l3 and points 37 on points 4%, when the system is in operating condition.v

The batteries 35. 36 operate the dynamotor-lei andheat the filaments of tubes 18, 19. 20 and battery 33 operates the telephone transmitter 32 and heats the filaments of the receiving 'tubes- All of the batteries discharge at the same rate because shunt resistance 15 is adjusted to increase the discharge rate of the battery 33 up to-thatof batteries 2:36. 46 is a voltmeter to indi-.

cate the conditionof charge of the batteries, atconstant load, and is a certain indicator, inasmuch as the batteries always discharge at thesaine rate- A mark on the dial indicates the operating pointbelow which the batteries should be chargedl For eliminatingcommutator ripple, the armature of dyni-unotor-l l isskew slotted, as about. tlu-ee-quarters of the slot pitch. which"inco'njunction with condensers15 and choke: 28;completely smooths out the ripple in-the dynamotor-output current so that it is not heard inthe local receiving set,

The 7 receiving filament wires 38 are twisted as shown, toprevent loW frequency induction in the receiving set from the Wires connected to batteries 35, 36, which-run the d ynamotor.

The receiving unit is equipped with'a comparatively small loop aerial which? maybe of the ordinary type but is preferably of one of the forms shown in Figs-1 and 2 The loop Fig. 1, is double with each half wound in the opposite direction and may be connected as indicated in circuit with a vari able tuning condenser 76 and loosely coupled through the coil 77 to the input circuit of the detector 51. If the loop 5 (Fig. 2) which is also double oppositely wound, is used instead of the loop 5 the free ends 49 and 150 of this loop are connected together and grounded, and the mid-point of the coil joined tothe lead 51 which establishes a connection to the grid of the detector tube 51 ot the receiver unit. The receiverloop (5 or 5) is shielded from local transmitter oscillations by any suitablemeans, but preferably by the electrostatic, open circuited shield or cage 52,'Fig. This shield consists of a special form of cage or coil of conductive material ada'pted'to entirely sur round the loop and be slightly spaced from it. The preferred construction comprises groups of spaced, parallel conductors connected in series with one end only of each group connected to the common grounded conductor-52. This arrangement provides an open circuited metallic cage surrounding the loop on all sides and serves to shield it from local transmitter energy without irnpairing its effectiveness for the reception of incoming signals. As indicated by the dotted lines in Fig. 1, the shield 52 may enclose the loop 5 and its tuning condenser 76. the remainder of the receiving equipment being enclosed in the metal box 47 provided with suitable openings to bring in the connections from the transmitter and power units and those from the desk telephone set.

The local oscillator 55 comprises a tube with inductance 56, variable capacityj57 to change its frequency, and receives plate-circuit power through the radio frequency choke coil 58 from battery The filament current. comes from battery 33 through switch points 39, 43, wires 38 in grounded metal covered conductors 60, and adjustable resistant-e61. The loop circuit is tuned by variable capacity 76 to the frequency of the incoming signal and is coupled to detector circuit through coil 7 7 Coil 77fa1so receives local oscillations from nearby circuit of tube to form an intermediate heterodyne beat frequency in the output circuit of detector This beat. frequency is amplified by tubes 63, 64, coupled by transformers 66. This intermediate frequency is then rectified by tube 67 coupled to the output circuit of tube 65 by transformer 68. 69 is an intermediate frequency by-pass condenser across the primary of transformer which couples tube 67 to audio frequency amplifier tube 71, the transformer 70 and tube 71 constituting an audio frequency stage of ampliiication. Transformer '72 adapts the output of tube 71 to telephone receiver 73. The filaments of tubes 55, 51, 63, 6 65, 67, 71 are heated by battery 33, while both parts of the battery 59, in series, supply plate current to tubes 55, 63, 64, 65, 71, and one part supplies plate current to tubes 51, 6?. All of the receiving tubes employ filament gridbias resistances 7-las shown to regulate the grid potentials.

The use of the local. oscillator 55 to heterodyne with the incoming signal frequency is of advantage in that it avoids the necessity of employing a predetermined difference between the incoming and outgoin frequencies, but the transmitter frequency can be employed with a proper frequency difference by cutting out oscillator 55 as by switch 7 5,.

and making the proper transmitter frequency adjustments. The main difficulty, however, in using the transmitter to heterodyne the incoming carrier wave, is in arranging the sending and receiving high frequency equipment to give the proper amplitude of local oscillations in tube 51 to produce maximum amplification, whereas by employing the local oscillator 55 the degree of coupling between the local oscillator circuit and 51 is such as to give maximum heterodyne amplification, and is fixed, no matter what are the conditions of installation of the equipment. Another advantage in employing the separate receiving oscillator is that the receiving set will function whether or not the transmitter is going. This permits the sta tion to be in condition for receiving a call When the transmitter is off. And still another advantage is that by excluding the transmitter radio frequency out of the receiver the latter can be connected by well known methods to an ordinary wire telephone system, without howling. The am plification of the beat frequency and then re-detection, is of advantage because of greater efficiency and quietness than either high frequency or audio frequency amp lification will afford. This applies particularly to short wave reception. For the longer waves, however, straight radio-frequency amplification is quite satisfactory for this system.

As shown in Figure 1, conductors connecting the receiving unit with the power and transmitting units are enclosed in metal sheathing to prevent the passage of high frequency currents. If the wires to telephone set 32, 7 3 are short no metal covering is necessary on them. In practice this provides a very compact and convenient receiving element capable of being installed on a roof, with suitable weather proofing, or in a room of a building with the transmitter set and the antenna on the roof at one side, without one interfering with the other. This is by reason of localizing the transmitter high frequency apparatus adjacent the antenna, which may either be run in connection with a ground as shown, or have a counterpoise, and controlling the transmission from wherever it is convenient to locate the operating position. If the transmitting and power units are separated somedistance, and the connecting conductors pass near the receiving unit, it will also be found neces sary to enclose these conductors in metal sheathing preferably grounded. The object of grounding, of course, is to prevent trans mitter radio frequency energy from passing through the sheathed conductors. The shielded receiving loop is at one side pointing at the distant station with one side ap proximately toward the the antenna to pick up little or no energy from the transmitter. In this connection, it is important to note that the master oscillator transmitting circuit with loosely coupled output transformer, or other means for confining the high frequency transmitter power to its own radiating circuit, in conjunction with the metal sheathed cables between the various units, effectively prevents paralysis of the receivingloop systemby the transmitter, even when located in and on the same building. Small loops in general and especially of the form disclosed herein are very desirable for receiving, in that they pick up much less induction, etc., in operating positions such as factories, than do antenna-ground systems. Loosely coupling the receiving set to the loop increases the selectivity, and is found desirable in locations where there is considerable interference from other stations and induction. In using loose coupling, as between the tuned loop and a secondary coil, care should be taken to avoid any stray capacity coupling. A preferred arrangement is to mount the little secondary coil 77 outside of the loop shield, together with the rest of the receiving equipment in a metal box, but this loose coupling can be anywhere in the high frequency circuits between the loop and the telephone receiver;

Should there be found to be interference with the receiver from a very powerful local transmitter the receiving and sending elements can be further separated, but can still be much closer together and give duplex communication, as with wire telephones, than has heretofore been possible with other systems proposed, which have required considerable separation of transmitter and receiver, and expansive land and construction.

After this system is once adjusted upon installation, no further operating adjustlong periods of time.

nients 1:51.136 'toun'd -necessary, excepting: over A power unit consolidated 1 for both sending-and-receivrng'is bGlH-BVCdtO. be new operating, as herein shown anddescribed. If

desirable a specially designed inotor-generator could be built to run on the-available source of gower a n'd-si-ipply suitablezpowcr to -ru-nthe equipment; but storage batteries Il-ILUO the 'ad vantage cl- --rez-idern.i 1 the communication vindependent of power supply interruptions.

WV-hat I claim is:

1. 1n duplex a-a'dio ;telephony, relatively power'tul means for radiating outgoing oscillationsand means for receivingincoming oscilations loatcd insu'chproximity that the-receiving means tends to be paralyzed by the outgoing oscillations, at telephone receiver connected to be responsive to the incoming oscillations and an adjacent telephone transn-ntterconnected tocontrol the outgoing oscillations, means t-or supplying power-to operate the sending and receiving systems,-sai il receiving means inclu-ding an antenna provided vwith an open clrcuited metallic shield.

In duplex radiotelephony, the combination eta sending element and a radio transmitter connected thereto, anrantenna providedwit-h an open circu-ited metallicshield, a radio receiver connected thereto. means for supplying power to thesystem, and a telephone transmitter and receiver.

3. In duplexradiotelephony, the combination of a transmitting elevated element, a ltKllO transmitter connected thereto, means tor-setting the-frequency of outgoing oscillations 7 independently of 1 the radiating circmt. characteristics, a loop-receiving circuit,

a shield including an open circuitedconductive member associated with said loop, a

power supply, and a telephone transmitter and receiver.

In duplex radiotelephony. the comhinatfon ot a radiating!-element,:aradiotransmitter circuit connected thereto, said'transmitten circuit including -a:masteroscillator, an amplifier and iarmodulatorameans:tor iinductively coupling the transmitter to said element.;a:rad-io receiving circuit having a loop antenna, an open circuited conductive shielding member enclosing said loop ani the @001) illlBlGOfvGIltklOSGCli by; pluralityuof preventing l local paralysis. of, the receiving independent conductive shielding members and the remainder of said circuit enclosed in asi-ngle conductive shielding; member? for circuit by the transmitter, a source 01 power,

and a telephone transmitter and receiver.

"6. In duplex radiotelephony, the combinationof a ra'diating element,: a radio 1 trainsni'itter connected: thereto, a; loosely. coupled output 1 transformer iliaving adjustable; secondary an d high impedance: primarywhen the secondary circuit is detuned, saidtransanit-tercomp risingan cscillatonyan amplifier -a'nt l zv n iodulator tube, a grid: leak regrriating resistance -u nit,-.a loop receiving circuit having 'mcans incl udingza grounded, open-.cin cuited, conductive shieldv for: PIQVGlltIllglO- 'cal paralysis of the. receiving circuitahy the transmitter, a-source otpower, and a telephone transmrittena-nd receiver.

' 7. 111 duplex radiotelephony, the combination of a: radiating elementzloosely coupled to a transmitter, said transmitter including a master oscillator a consolidated power 'unit' tor thesystem, a receiving unitiliavi'ng a loop antenna. shielding means tor prevent in; electrostatic coupling lJGtWGGIhSZl-ldrtiflltenna and adjacent metallic objects, means for loosely coupling the antenna; tozthe re- 'ceiving circuit. from .the outside of said shielding means," the conductors passing between tliepower and receiving 'unitsubeinzg shielded,and-a telephone transmitter and receiver.

*8. In duplex: ra'diotelephony, the combiiua :tion of a radio. transn'iitter .andaa radiating element, double oppositely wound. receivlng loop havinga receiving set coupled thereto, aconsolidatedipomver unit contain ing dynamotor and -:storage batteries for energizing both the receiver and transmitter,

-'sheathed conductors passing between .the transmitting, power and receiving un-1ts,- the conductor-sin the power unit which :go to the I T0081 ving :unitbeing twisted in a manner to namotor no ses. in the receiving prevent d set, and iii telephone transmitter .and receiver.

- 9. \In duplex radiotelephony, the combination of a transmitterwand a radiating. eletenua. a source of power opcratively connectment, a shielded loop positioned so as to prevent local paralysis of the receiving set connected thereto, a consolidated power unit CO'l'l'lPllSlIlg storage batteries and a dynan'iotorfthe dynai'notor armaturebeing skew slotted, condensers shunted across both the input and output side of'the dynamotor, the high voltage circuit containing a low frequency choke coil. and a telephone trans mitter and receiver.

10. A duplex radio telephone station comprising separate transmitting and receiving elements. means tor preventing local paralysisof the receiving set by the transmitter,

the receiving set consisting of a double, op-

loosely coupled thereto through an output transformer, a separate receiving set co1nprising a local oscillator, a receiving loop shielded from the transmitter oscillations, amplifying and telepl'ione detec ing means, a telephone transmitter controlling the outgoing oscillations through a power modulator, a power unit supplying the transmit-- ting and receiving circuits, and means for preventing the transmitting power from a ffecting the detection of the received signal oscillations.

13. In duplex radio telephony, the combination of a 'adio transmitter unit having a radiz iting antenna, a radio rcceiring unithaving a. loop antenna, a conmion piivver supply for both said units, switch means for controlling the supply of power to each unit, rely means including a switch hook for remotely controlling the switch means, a telephone transmitter and receiver opcratively connected "to the transmitting and receiving circuits, said receiver enacting with said switch hook in such manner as to cause said relay means to open or close said switch means.

1.4:. The combination With a relatively powerful source of oscillations and a radiating element therefor for transmitting, of a loop receiving element adjacent said element and \vithin the field thereof positioned relatively to said element as to receive a minimum of local transmitter energy, amplifying and detecting means connected to said loop, and means for-shielding the receiving "system from local transmitter high frequency oscillations from said radiating element including an open circuited wire cage surrounding said loop receiving element.

l5. In radio telephony, the combination of it separately excited power amplifying circuit delivering continuous carrier wave scillations to a radiating element through an output power transformer, a loop receiving element positioned to pick up a mini mum of local trai'ismitter energy and tuned to receive a different incoming frequency, a power supply, and grounded, open circuited shielding means for preventing local paralysis of said element.

16. A duplex radio telephone station consisting of tral'ismitting, power and receiving units, the transmitting unit having means for generating outgoing modulated oscillations controlled by a telephone transmitter and. an oscillator for setting the frequency independently of antenna circuit character istics, the receiving unit consistii'ig of a Sllleltltll loop, detector and amplifier and telephone receiver, the units being co.u ncctcd by power supply and control wires and means for preventing high frequei'icy oscillations from passing through said wires, :1 switch hook for said receiver, and switching means operated by said hook for energizing or decnergizing the traiisniitting and receiving eircui s simultaneously when the receiver is removed from or replaced on said hook.

1T. lira duplex radiotelephone system including a. transmitting set, loop receiving and a cmnmon source of power suppli for both said sets, the l'llGlillOClOf operating said system Without paralyzing the receiving by local "transmitted energy which consists in balancing out said traiismittei'l energy in the power supply circuit and in the loop circuit, shielding the receiving circuit in a closed circuited metallic conductor and shielding the loop circuit in an open circuited metallic conductor.

Signed. at New York in the county ol New York andstate of New York this 26th day of August A. D. 1921 PAUL XVARE.

Ill)

CERTIFIGATE Gi CGRRECTIQN.

Patent No. 1,627,718. Granted May 10, 1927, to

PAUL WARE.

It is hereby certified that error apgiears in the printed specification of the above numbered patent requiring correction as follows: ?age 3, line 17, before the words "The positive" insert the Words "27 are radio frequency ehoke coiis"; page 4, line 88, strike out the article "the second occurrence; page 6, line 15, claim 12, for the word "amplified" reaii "amplifier"; and that the said Letters Patent should be read with these eorreetieie therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 31st day of May, A. D. 1927.

M. J. Moore, Seal. Acting Gommiseioner of Patents.

I GERTIFIGATE 8F GURREGTION.

Patent No. 1,627,718. Granted May 10, 1927, to

PAUL WARE.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: iage 3, line 17, before the words "The positive" insert the words "27 are radio frequency choke coils"; page 4, line 88, strike out the article "the" second occurrence; page 6, line 1b, claim 12, for the word "ampiified reed "ampiiiier"; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 31st day of May, A. D. 1927.

v M. J. Moore, Seal. Acting Commissioner of Patents.

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