US1581576A - Carrier-wave signaling system - Google Patents

Description

A ril 20, 1926.

J w. HoR'roN CARRIER WAVE SIGNALING SYQTEM 2 Sheets-Sheet 1 Filed March 18, 1922 coo mw a 7l//7/0/ Joseph WHO/400 April 20, 1926.

J-. w. HORTON CARRIER WAVE smumme 's'YsTEM Filed March 18, 1922 Patented Apr. 20, 1926.

. UNIT-ED. STATES PATENT. o

FF'ICEF.

.rosnrn wurron'roiv, or EAST ORANGE, NEW JERSEY, .ASSIGNOR TO wnsrnnn ELEC- TRIO COMPANY, YORK.

mconronunn, or unwvonx, n. Y., A conrom'rron 'or new shaman-wave sronamne srs rnm. I I 3 Application flledltarch 1a, 1922. Ser1a1.No."5 44,709.-

To all whom it may-concern:

Be it known that I, JOSEPH W.'HORTON, a

' citizen of the United States, residing at East Orange,-- in the county of Essex,- St-ate of New Jersey, have invented certain new and useful Improvements in a Carrier-Wave Signaling System of which the following is a full. clear, concise, and exact description.

The present invention relates to high fre quency or carrier wave signaling in which carrier waves of a plurality of frequencies are employed.

The invention is particularly applicable to systems in which carrier waves of differ ent frequencies'are used for transmission in opposite directions.

A feature ofthe invention is the arrangement by which a single translating-circuit is made to oscillate at two distinct carrier wave frequencies both of which are em. ployed for signaling.

' More specifically the translatingcircuitof the invention comprises a vacuum discharge tube modulator-demodulator arranged to oscillate' at' two distinct carrier frequencies,

the carrier wave of one frequency be ng, used to transmit signals, and the wave of the" other, generated frequency being combined with received carrier waves to enable reception of the signals The 3 generated wave used in signal reception is preferably of the same frequency as the carrier wave, the modulations of which represent thesignals to be received.

The oscillator-modulator-demodulator of the invention is preferably gt-a, balanced-cir- I cuit type arranged to, suppress transmission of each carrier wave.but to produce" and transmit the side-band components I resulting from the impression of signaling voltage variations thereon. These signaling waves or variations comprise both the received side-band components from a distant'sta tion,-which combine with the generated wave of the roper frequency in accordance with the we l-known hoxfnodyne action to enable reception of the signals, and low-fre .uency signal waves such for example as speec cur rent waves which modulate the carrier wave of the transmitting frequency to produce side bands for transmission to the distant station. Suitable filters are connected between the translating circuit and the high frequency terminal to prevent return of the outgoing sideband components to the receiving side of the translating circuit.

The invention is applicable particularly to a carrier currentsystem havmg 'a' singleor a plurality of two-waychanne1s eacnemploying different transmitting and receiving friequencies, and the invention will be described below as embodied. in a'te'rminal circuit for such a system, as [a monitoring circuit for a mid-line repeater station in such a systen1, and-as'a portable set for use in such a system. The various features and ob ects of the invention. will be clear from carrier line, Fig. 1 showing theapplio'ation toa terminal circuit; Fig} 2 to a monitoring circuit for a mid-line repeater to a portable signaling circuit.

The line ML is'a multiplex carrier transmission line having the channel apparatus arranged so that the channels used. for transmission 1n one directlon employ frequencies.

grouped in one frequency range, while the channels used for transmission in the op,

posite direction have their frequencies and Fig. 3

grouped in a different range. It will be assumed that the. channels transmitting over the line ML. tothe right in Figs. .1 and 2 wards, while the channels transmitting to the .left employ frequencies from 20,000 cycle-s downward. q

Referring now to Fig. 1 terminal circuits for two carrierchannels C and C cooperating with two low frequency lines LL and LL respectively are indicated. Other, channels may be added to the line ML in a similar manner as may be desired. It is assumed in the present instance that the carrier waves for the. entire system are employ frequencies from 23,333 cycles up-,

multiples of 3,333 cycles although any other" suitable frequency scheme may be used and if desired the frequency spacin between carriers may be non-uniform. T e channel C is indicated as employing a carrier frequency of the third multiple o1"'1 0,000 cycles for receiving from the line ML, while channel C employs the fourth multiple or har- Each of these channels uses the lower side band for reception. For transmission these monic, a frequency of 13,333 for receiving.v

channels use respectively 23,333 or the seventh harmonic and 26,666 or the eighth harmonic and. are arranged to transmit the' upper side bands. Receiving band filters BF and BF arranged to pass the respec-* tive receiving frequencies and transmittingfilters BF and BF designed to pass the corresponding transmittin frequencies serve to connect the respective c annels C and C with the main line. These and the other filters indicated throughout the system may 'be designed in accordance with the principles disclosed in the patent to G. A. Campbell, No. 1,227,113, granted May 22, 1917.

Except for the .frequencies which they employ, channels '0} and C may be duplicates of each other, and it will 'sufiice to describe the circuit of channel C The filter and the line balancing network N BF leads to a common input circuit 10 of the translating circuit OMD while the output side of this translating. circuit is connected to a common outgoing circuit 11 leading to the transmitting filter'BF. The circuits 10 and 11 are connected through low pass filters LP and LP with the line-LL,

through the msual duplex connectioncom-.

prising the three-winding repeating coilTll-ll e filters LP. and LP are'designed to pass freely currents of the frequencies employed by the line LL such as speech frequencies but to oppose transmission ot the carrier current.

The translating circuit proper included between the ,common incoming and out oin circuits 10 and 11 consists of a comb oscillator-modulator-demodulator circuit ar-' ranged to oscillate simultaneously at frequencies of 10,000 cycles and 23,333, these being the frequencies of the carrier waves used by the channel C The common translating circuit is shown as comprising a balanced vacuum tube circuit including the tuned feed back circuit 18 and regulating esistance 19 to the same point of the out at primary winding. The. anodes of the erminalsof the primary windingof the output coupling 17 through the large con densers 20 21, the space current being supplied to anodes from the source indicated, through the respective chokes 22 and 23. The common portion of the grid .feed back circuits. the oscillations follow is as a (we stated we wo tubes are connected to the respective circuits included between the cathodes and the input coil contains a secondary win ing 24 coupled to the feed back circuit 1 a secondary winding 25 coupled to the feed back circuit 18, and if deslred may contain a grid resistance 26 and a grid battery as indicated.

It is a characteristic of a balanced circuit of the type indicated that the outgoing coil 17 and also the input coil 14 are balanced as to voltages applied to the common portion 24, 25,26 of the grid circuit, provided of course, that the tubes and the rest of the circuit are properly balanced. Similarly the connections between the common cathode connection and the mid-point of the primary winding of coil- 17 including in one case the tuned circuit 15 and in the other case the tuned circuit 18 are neutral with respect to' the circuits 10- and 11. However, voltage variations impressed on the common portion 24, 25, 26 of the grid circuit are re- 'peated in amplifiedform into the two anode branches 15, 16 and 18, 19. By tuning the circuit 15'to one frequency, say 10,000 cycles and the circuit 18 to a different frequency, for example, 23,333, the translating circuit may be made to oscillate independently at both of these frequencies, since output energy in the tuned circuits is returned,

in part to the input branch which is so related to the restof thecircuit as to exercise control over the anode-current supplying the Since the 'ath which neutral with respect to the circuits'lO and 11, the waves locally generated are confined to the translating circuit and are prevented 1' from passing into either circuit 10 or 11.

In addition to serving as a generator of oscillations, the common translating circuit OMD also serves to modulate the transmitted carrier wave and to detect or demodulate the received ,carrier wave employed by the channel C The operation of the circuit in these two manners will be clear from following the path taken by currents in the course of transmission and reception, the operation of the translating circuit as an oscillator having already been described.

Signaling currents such as speech. cur-.

rents received from the telephone line LL pass through the filter LP to the circuit 10,

ut are prevented from reaching the line ML on account of the filter BF which has a transmission range abovethat of the filter LP; Speech currents are impressed on the in ut coil 14, causing the potentialsof the grids of the tubes 12 and'13 to vary-in an opposite manner to each other and fproducing complemental impedance variations in the tubes -12 and 13, In this manner the translating circuit is unbalanced to an extent depending on the amplitude of the impressed potential and each of the waves generated by the circuit is transmitted to the outgoing circuit-11 to an extent substantially proportional to the impressed voltage variation. As long as speech currents are impressed pn thefcoil 14, two modulated high frequency waves are thus produced in the outgoing circuit 11.} The modulated wave produced by the combination of the voice waves with the generated wave of 10,000 cycles is dissipated in the circuit 11 and does not find its way to either the lines LL or ML on account of the filters LP and BF Assuming that the principal component frequencies of speech do not exceed an upper limit of about 2200 cycles, the

' modulated wave components due to the modulations of the generated wave of frequency 23,333 by the impressed voice com: prise an upper side band and a lower side band made up principally of frequencies comprising respectively a range from near the carrier frequency to a frequency about 2200 cycles lower than the carrier frequency and a range from near the carrier frequency to a frequency about 2200 cycles higher than the carrier-frequency. The band filter BF is arranged to pass only the upper of these two side bands and the upper side band 'of the outgoing carrier frequency is in this manner impressed 0n the line ML.

It is assumed that the distant station is a duplicate of the station shown in. Fig. 1 except that the channel C at that station is arranged to receive and to transmit currents of the same frequencies that are respectively transmitted and received by the channel C of the station under consideration. Under these conditions the distant station will transmit to the line ML a voicemodulated wave frequency of 10,000cycles in a manner entirely similar to that described in connection with the channel C of Fig. 1 for transmitting the upper side band of the car rier 23,333. The wave so impressed on the line ML at the distant station and received at the terminal shown in Fig. 1 is selectively transmitted by thejfrlter BF into the circuit 10 but is prevented from bein transmitted by any of the other filters. he received side band is prevented by the filter LP from reaching the line LL but is impressed on the input 'coil 14. These im-- pressed waves interact with the waves generated in the common translating circuit OMD and in accordance witlrthe wellknown homodyne action, if the generated produce currents within the range of either the voice filter LP or band filter- BF, and

such currents are dissipated in the'local circuit 11. The voice currents resulting from the detecting o'r demodulating of the com-v mon translating circuit as described, pass through the filter LPand are impressed on Y the'telephone line LL f Therepeating coil'H thebalancing net- I work'N the low pass filters LP and the commontranslating circuit OMD, of the channel C correspond to similarly designated elements of the channel C and operate in an entirely similar 'manner except that the waves generated in the circuit OMD 26,666 respectively. v

In Fig. 2'the line ML, which may bethe same line as that indicated in Fig. 1, is shown' divided into two sections between which are inserted two one-way repeaters ER and WR for amplifying the waves trans- The common translating circuit OMD inserted between the incoming and outgoing circuits 30 and 31' respectively may be entirely similar to the circuit OMD which would in practice. have a fixed frequency setting, whereas the circuit OMD is intendedto have the frequencies ofthe waves which, are generated readily adjustable, as by means of the condensers 32 and 33. The operators set, ccmprising a transmittter T, receiver R and a propriate connections therefor, is connecte t9 the balanced three-windin repeats ing coil H to the other side of w ich' the balancing network N is-provided. The coil H? is connected through voice filters LP and LP to the circuits 30 and 31 in the same way that the line LL of Fig. lis' connected to thecircuits 10 and 11,. The circuit 30 terminates in the plug 35 of the twin plug P? and also in plug 36 of the twin plug P The incoming circuit 31 is similarly connected to thefplugs 38 and 39. Channel taps termimating in jacks J are rovided for some orall of the channelsatt e repeater station, these jacks being connected to the line ML through channel filters'yBF BF etc. I

The operation of the circuit of Fig. '2 is as follows. If it is assumed that the attendant at the repeater station desires to communicateover channel C for example,-he will insert the plug P so that plug 38 connects with the associated jack leading to the filter BF and the plug 35 connects to the filter BF, and he inserts plug P so that plug 36 makes connection with the associated filter ,have in this case frequencies of 13,333 and 5. the-{portable set is to be used channel taps mon translating circuit OMD where it interacts with the locally generated wave of the carrier frequency to produce speech currents in the outgoing circuit 30. These speech currents pass through the filter L1 to the receiverflR 'of the attendants telein the circuit OMD phone. A transmission originating in channel C to the right of Fig. 2 passes selectively into the band filter BF shown to the right of the repeater, terminals of plug 39, incoming circuit 31 and common translating device OMD where the receiving currents interactwith the locally generated wave of the carrier frequency and produce speech currents in the circuit These are received as before on the attendants set.

'If'the attendant desires to talk in either direction over the line ML through thecham nel C having first adjustedthe condensers 32'and 33' as required by this channel, he speaks into the transmitter T of his set, the speech currents pass through the coil H and the filter LP to the common input circuit 31 and modulate both of the generated waves The lower side band produced by "modulation of the wave of 10,000 cycles passes from circuit 30 selectively through the band filter BF and is impressed upon the west linesection ML. The modulated wave produced by modulation of the wave of 23,333 passes selectively through the filter BF and is impressed on the east section of the line ML. It is seen,

therefore, that the attendant may both listen and talk over both sections of the main line ML through the channel C and it is obvious that by plugging into the filters of another channel such as the filters BF- and BF of the channel C and by properly adjusting the condensers 32 and 33 to cause the generation of carrier waves of the frequencies employed on this channel, the attendant can communicate in a similar manner over another channel.

Fig. 3 illustrates. a portable signaling set of convenient form to which the invention readily lends itself. As in the case of the other figures, the circuit of this figure is intended for use in connection With a carrier system employing different frequencies for opposite directions of transmission, the arrangement commonly met with in the socalled grouped frequency systems. It is assumed that at points on a system where Transmission originating in including filters and jacks, such as the jacks J shown on Fig. 2, will-be provided and the plug P is designed for insertion into a pair of jacks serving as taps for the two'sides of a two-way channel. F or communicating over channels employing different frequencies the translating circuit of F ig. 3 is arranged, as in the case of the other figures.

to oscillate at two'distinct frequencies, and

-48 and has keys, as shown, for selectively throwing these condensers into the circuit so that the translating device oscillates under control of this feed-back circuit also at any of the channel frequenciesof the system.

In the circuit of Fig. 3 no low frequency telephone balance is provided as in the other.

figures but a relay 49., controlled from key K on the hand microphone set comprising receiver R and transmitter T controls, by its armature, the connection of the second-. ary winding ofeither feed-back coil 41 or 45 so that the translating circuit oscillates at one frequency when the relay is'deenergized and at another frequency when the relay 49 is energized provided the ca acity included in circuit due'to the connection of the condensers 42, 43 and 44 difiers from that provided by the connection of the condensers 46, 47 and 48. The filters LP, LP- transmit speech frequencies but prevent the transmission of any of the carrier frequenc1es.

In operation thev twin plug P is inserted into apair of jacks of the two one-way channels with which communication is desired and certain of the condensers 42, 43 and 44 are connected in circuit to cause the translating-circuit to oscillate at the carrier frequency of the channel over which it is desired to receive. Similarly, certain of the condensers 46, 47 and 48 are connected in.

circuit to cause the translating device to escillate at the carrier frequency of the transmittin channel. The operator, in listening, 9.1 ows the ke K to remain open and the armature of tie relay 49 is, therefore, against its back contact, making the feedback coil 41 operative to cause the circuit to oscillate at the receivin carrier -fre quency. Current received from the"l ine passes through the channel tap including The feed-back coupling 45 has as-' the channel filter and jack to which the plug 51 is connected and to the input coil 52, the

' lowermost filter LP blocking the transmission of this current through its circuit. From the coupling 52 the received side band is impressed upon the translating circuit and due to the interaction between the received side band and the generated wave, voice frequency currents are produced in the output coil 58. These pass through the uppermost of the filters LP to the receiver R \Vhcn the operator desires to talk he presses the key K, causing energization of relay 49 which shifts its armature so' as to connect the secondary winding of feed-backcoil 45 into the grid circuit, causing the translating device to oscillate at the transmitting carrier frequency. Voice currents produced in-the circuit of the microphone T pass throu h the filter LP to the input circuit 52 an modulate the locally produced carrier wave. The resulting side band is transmitted to the coupling 53 and the plug 55 to the jack of the outgoing channel tap.

In the foregoing description of the operation of the portable translating device shown in Fig. 3, it was assumed that the high fresuency line was provided with channel taps including channel filters such as are shown in Fig. 2. These filters act in the manner described in connection with other figures to direct the carrier and speech frequencies along their proper paths. associated with the translating circuit. In case the line is not provided with channel filters it is still possible to use the translating device of Fig. 3 by inserting the plug P into a jack connected directly across the line and Without the interposition of any channel filters, although it may be advantageous to have a high pass filter inserted between the jack and the line in the case where the high frequency line serves to transmit an ordinary loW frequency telephone conversation in addition to the various carrier transmissions. With the plug P disconnected from the system and the plug P connected as described, the relay 56 being deenergized, currentsof the frequencies of all of the channels enter the circuit of the translating device through the terminals of the plug P, the right-hand contacts of relay 56, the incoming connection of the translating circuit to the coil 52, and are impressed on the circuit of the translating device. By the well-known homodyne action the received carrier wave having the same-frequency and phase as the locally generated wave, will yield its modulation components, that is,

resulting components will have frequencies of the order of the frequency difference between adjacent channels or still higher, and will, therefore, be prevented from passing into the receiving circuit by the associated filter LP. The speech that is received is, therefore, that represented by the modulating of the particular wave of the frequency at which the translating device oscillates when receiving and the speech of this particular channel is selectively received. By tuning the feed-back circuit of the translating device to other carrier frequencies the speech of any other of the channels may similarly be received. The higher frequency components produced in the translating circuit by the interaction of the different channel frequencies are prevented from passing again to the line, since the relay 56is deenergized and the outgoing circuit from the coil 53 is broken atthe lefthand contacts of this relay.

As stated above, the operator presses the key K during the transmitting interval. In case the plug P is being used, it is neces- 'sary also to close the contact 57 in the cirswitch the connection of the plug P from the receiving side to the transmitting side of the translating circuit. For convenience in the arrangement of the drawing, the contact 57 is shown apart from the key K, but

in practice the two springs of contact' '57 would be arranged behind the button of. the 1 key K, but suitably insulated therefrom, in "such a manner that when the key is de' pressed the contact 57 is closed, such double contact key arrangements being common and well-known in the art. Having depressed key K and closed contact 57 causing energization of relays 49 and 56, the operator proceeds to talk against the transmitter T \Vith the relay 49 energized the feed-back coil 45 bccomes effective to cause the translating device to oscillate at the transmitting frequencyand speech currents from the circuit of the transmitter '1 pass through the coil 52 and modulate the wave of the trans- -mitting frequency. The resulting modulated carrier wave is' 'transmitted through the coil 53, the left-hand contacts of relay 56 now closed, the terminal of plug P l and of the jack with which it is assumedztb be connected, and to the main line. The frighthand contacts of the relay 56, beingnow open, the outgoing current, is prevented from passing again into the input circuit of the translating device.

It will be obvious that the variable condensers in the circuit OMB, for exam le, may be replaced if desired by keys and'zI ifferent fixed or variable capacities arranged as in the circuit of Fig. 3, or vice versa.

3 Further, it isto be understood that the circuits shown and described are merely illustrative of the preferred forms of practising the invention, butthat neither the prising a self-oscillating vacuum tube modulator comprising a pair of space dischar e paths connected in balanced 1813121011 wit I respect to the incoming and outgoing circuits a'rrangedto oscillate at two di connected in cuits having a: pair of feed-back c ir'cuitsdifferentl tuned to enable it to oscillate at two di erent carrier wave frequencies.

.2. A combined oscillator-modulator comprising a self-oscillating vacuum tubemodulator comprising a pair of space discharge.

paths connected in balanced relation with respect to the incoming and outgoing cirerent carrier wave frequencies in combination with means for impre'ssing thereon signaling waves to combine with both carrier waves.

3. A combined oscillator-modulator comrising a self-oscillatin ator arranged to oscil ate at two different carrier wave frequencies and having means for impressing signaling voltage variations thereon to produce side band frequency components of both of said waves, said osc illator-modulator having a balanced circuit arrangement to suppress transmission of the 'unmodulated carrier components of both waves, but to transmit the side band components. p

4. A combined oscillator-modulator comprising a pair of cathode-grid-anode tubes and a plurality of selective feed-backcircuits for impressingldifierent frequencies on the grids to cause is e tubes to oscillate at a plurality of carrier wave frequencies and means to impresssi al voltage variations on the grids to mo ulate the said carrier waves. I

5. A translating circuit comprising a. vacuum discharge tube modulator comprising a pbair of space discharge paths connected in alanced relation with respect to the incoming and outgoing circuits arranged to oscillate simultaneously at a plurality of wave frequencies and means for impressing .signal voltage variations on said modulator *gto produce combination frequencies with ieach of the generatedwaves.

6. In a signalling system a combined os- 'cillator-modulator comprising a self-oscillat in modulator arranged to oscillate at a pluraity of different wave frequencies, means to im ress signal volta e variations on said modu ator to produce side band "components with each of the generated waves, and an outgoing circuit, said oscillator-modulator comprising a pair of space discharge paths vacuum tube modu balanced or ush-pull relation meii connected in balanced relation :with respect to the incoming and outgoing circuits arranged to suppress the transmission of the unmodulated component of each ofsaid generated waves to said outgoing circuit but to transmit theside band com onents thereto. 7. A two-way trans ating circuit for a two-way channel employing different carrier frequencies for transmitting and receiving, comprising a self-oscillating moduwlator having input and output circuit branches connected to the respective sides of saidchannel, said modulator having. a pair of feed-back circuits differently tuned to enable it to oscillate at two difl'erent frequencies corresponding respectively to the receiving and transmitting channel frequenc1es.-. i

8. A combined oscillator-demodulator comprising a self-oscillating vacuum tube demodulator comprising a pair of discharge paths'connected in balanced relation with 'way translating circuit comprising a sclfr oscillatin vacuum tube modulator-demodulator having an input and an output circuit, a signaling-frequency and a carrier-freuency incoming circuit each connected to t e input circuit, a signaling-frequency and a carrier-frequency outgoing circuit each connected to the output circuit, the outgoing carrier frequency being different from the incoming carrier frequency, said vacuum tube circuit being arranged to oscillate at both of said carrier frequencies.

10.A two-way translating circuit as claimed in claim 9, a signaling-frequency filter being included in each of said incoming and outgoing signaling-frequency circuits and a carrier-frequency filter being included in-ea'ch of said incoming and outgoing carrier-frequency circuits, each of said latter two filtersbemg arranged to pass freely the carrier frequency of the'circuit in which it is connected, but to block transmlssion of current of the signaling frequency of the other' carrier frequency 11. In combination a. self-oscillating vacuum tube modulator-demodulator circuit having an input and an output circuit, a signaling frequency circuit connected to both said input and said output circuits, the connection to each of said two last-mentioned circuits containing a signaling-frequency filter, a carrier line connected to both said input and said output circuits, the connections'to said last-mentioned circuits including each a filter of a different carrier frequency, said tube circuit being arranged to oscillate at both of said-carrier frequencies.

12. An arrangement as claimed in claim 11, said modulator-demodulator circuit having a balanced circuit arrangement to suppress the unmodulated carrier component of each of said carrier waves, but to permit transmission of side band frequency components.

13. The combination with a mid-line repeater for a multiplex carrier line employing carrier waves of different frequencies for oppositely directed transmissions, of a monitoring circuit comprising a two-way selfoscillating translating device having an input and an output circuit, channel taps at said repeater, switching means for connecting said input circuit to each of two oppositely directed channels, means to adjust said translating device to oscillate at the frequencies of both of said channels, a telephone set connected to said output circuit and a voice filter included in the connection to said set.

14. The combination with a mid-line repeater for a multiplex carrier line employing carrier waves of different frequencies for oppositely directed transmissions, of a monitoring circuit comprisin a two-Way self-oscillating translating device having an input and an output circuit, channel taps at said repeater switch, means for connecting said output circuit to each of two opposltely directed channels, means to ad ust' said translating device to oscillate at the fre uen-- cics of both of said channels, a telep one set connected to said input circuit and a voice filter included in the connection to said set."

15. A combined oscillating and modulating circuit comprising a self-oscillating vacuum tube circuit having means for generating a carrierwave for transmission and a wave of a different carrier frequency for receiving and having means for impressing signaling voltage variations thereon for modulating the first mentioned carrier wave for transmission and for impressing received Wave modulations thereon for interacting with the second mentioned carrier for controlling said oscillations and modulated waves to be demodulated.

' 17. A translating system common to an input and an output circuit, said'translating system comprising a combined oscillatormodulator-demodulator comprising a pair of space discharge paths connected in balanced relation with respect to said input and output circuit, arranged to oscillate simultaneously at two different carrier frequencies and means for impressing voltage variations on said discharge paths to produce combination frequencies with each of said carrier frequencies.

In witness whereof, I hereunto'subscribe my name this 15th day of March A. D.,

J OSEPH W. HORTON.

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