US1593365A - Method and system of high-frequency transmission - Google Patents

Description

July 20 1926.

E. O. SCRIVEN METHOD AND SYSTEM OF HIGH FREQUENCY TRANSMISSION 2 Sheets-Sheet'l Filed Sept. 29 1919 //7 1/6 n/ar. [mm/0 0 Sam en.

E. O. SCRIVEN METHOD AND SYSTEM OF HIGH FREQUENCY TRANSMISSION Filed Sept. 29 1919 2 Sheets-Sheet 2 IHI HIE

/m/e/7/0r: Edward O. Jeni/en @QXT/ A f/fy UITE STAT I:

A'FNT F F E C E EDWARD o. soRIvEn, OF NEW YORK, N. 2., ASSIGNOR 'ro WESTERN ELECTRIC oom- PANY, INCORPORATED, on NEW YORK, N. Y., A CORPORATION OF NEW YORK.

METHOD AND SYSTEE OF HIGH-FREQUENCY TRANSMISSION.

Application filed September 29, 1919. Serial No. 327,039.

This invention relates to methods and systems of. high frequency transmission and more particularly to multiplex carrier wave signaling in which high frequency reinforcing oscillations of the carrier frequency are combined at a receiving station with the received carrier oscillations.

An object of the invention is to make possible two-way transmission with the same .carrier frequency and at the same time to secure an exact correspondence in frequency between the carrier frequency of the oscillations received at each station and the reinforcing oscillations at that station.

A feature of the invention is the derivation of all of the carrier and reinforcing oscillations used in a multiplex system at both terminals of the high frequency line or both radio stations, as the case may be, from control oscillations produced by a single oscillator.

A further feature of the invention is the arrangementwhereby the reinforcing oscillations are applied to the output circuit of a uni-directionally conducting detector or demodulator in order to prevent transmission of these reinforcing oscillations to the high frequency line.

According to the present invention, the different frequency carrier oscillations or carrier waves are produced by first generating oscillations called base frequency or control" oscillations as. for example, 5000 cycles. These base frequency oscillations are then distort-ed to produce harmonic frequency oscillations as, for example. of 10,000, 15.000 and 20.000 cycles, and the harmonic frequency oscillations are then separated so that oscillations of one particular harmonic frequency may serve as one carrier wave and oscillations of other harmonic frequencies as other individual carrier waves. It is desirable to be able to carry ontwo-way communication using waves of the same carrier frequency for transmission in each direction. This may be accomplished by transmitting part of the base frequency oscillations from the station where they are produced to the receiving station with which communication is to be maintained. At the receiving station. the re* ceived base frequency oscillations are distorted iii-the samefmanner as at the transmitting station to produce carrier waves for the return transmission.

According to the method of carrier wave reception termed homodyne, the amplitude of the signal obtained from the received carrier wave when detected or demodulated is intensified by combining the modified or modulated carrier wave oscillations as received with locally generated reinforcing oscillations of the carrier frequency. This method of reception is disclosed and claimed in United States Patent 1.330.471. patented February 10, 1920, to B. \V. Kendall. If these locally generated or reinforcing oscillations differ in frequency from the carrier frequency of the received oscillations, beats of the difference frequency are produced and may be manifested as a sound or noise which interferes with a distinct reception of the signal. An important feature of this invention lies in the use of a portion of the carrier wave oscillations produced at a station to reinforce the modified oscillations of the same carrier frequency received at that station. It will, therefore, be clear that all of the carrier oscillations transmitted in both directions in the various two-way transmissions of a multiplex system as well as the reinforcing 0scillations supplied to the receiving circuits are derived primarily from a single source, the base-frequency oscillator. The power output of the base-frequency oscillator may, 7

however. be "cry small. since amplifiers operating substantially without distortion are available to increase the magnitude of a fluctuating current to any desired degree.

It is frequently highly desirable that no oscillations of the carrier frequency be transmitted through the ether or over the conducting multiplex circuit, as the case may be, except during transmission of signals or control impulses. It is further desirable that during the transmission of sig nals or control energy, the envelope of the modified carrier oscillations, as transmitted, be directly proportional to the signal or control impulses or, in other words, that there be no unmodulated component of the transmitted carrier wave. The first of these objects, namely, the prevention of transmission of carrier frequency oscillations, except during intentional transmission, is accomplished by two different expedients. For the outgoing high frequency channel, a modulator of the general balanced type disclosed in United States Patent 1,343,306, patented June 15, 1920, to J. R. Carson, is used. This modulator is placed between the source of carrier oscillations and the higdh frequency line of transmitting antenna an the high fre uency line except as modified or modulate waves varying substantially in direct proportion to the low frequency waves or impulses impressed on the modulator. For thenincoming channel, a unidirectionally conducting detector or demodulator, referably of the thermionic type, is use and the local source of reinforcing oscillations is connected to its output circuit and is thus prevented by the umdirectionally conducting characteristic of the detector from supplying high frequency oscillations back through it to the high frequency line. It follows, therefore, that waves of carrier frequency are excluded from the high frequency line except during signal or control transmission and that during such transmission, the envelope ampli-' tude of the high frequency carrier wave is directly proportional to the signal or control wave.

This invention is a plicable to telephony, telegraphy or any ot er form of electrical signaling or transmission. Although useful for radio signaling, it is of particular importance in wire line signaling, not only in that it enables a number of telephone or other communications to be carried on simultaneously, but also because this multiplex carrier system may be applied to present day signaling lines, thus increasing the number of messages which they may transmit without interfering with'the ordinary lower frequency signal currents which they at present use.

In the drawing, Fig. 1 illustrates diagrammatically, the circuits and apparatus at one terminal of an ordinary signal line on which the high frequency system of the present invention has been composited, and Fig. 2 illustratesdiagrammatically, the circuits at the opposite terminal of the same composited line but with certain modifications. Referring to Fig. 1, the ordinary signal line to be composited is indicated at 1. A low frequency line 2 of the usual type indicated as a telephone line is connected by two-way repeating apparatus 3 including three-element vacuum tube amplifiers of the thermionic type to incoming channel 4 and outgoing 'channel 5 which are conjugately connected to composited line 1. Both lines 1 and 2 are balanced with respect to their conjugate connections by networks N each of which simulates the characteristic impedance of the line which it serves to balrmits no carrier waves to pass to.

ance for currents of all frequencies transmitted by that line. Since high frequency currents are also to be transmitted over channels 4 and 5, it is necessary to provide means to exclude them from line 2 and its connections which might otherwise dissipate their energy. Such high frequency currents are excluded from the incoming side of the repeater 3 by a low pass filter of the type described in U. S. patent to Campbell, No. 1,227,113 patented May 22, 1917. This particular filter consists of a plurality of similar sections each having series inductance and shunt capacity and its electrical characteristics are such that it transmits currents of the range of essential speech frequencies as, for example, 100 cycles up to 2500 cycles with negligible attenuation. while substantially excluding currents of all frequencies outside this range. High frequency currents in outgoing channel 5 are excluded from the outgoing side of repeater 3 by reason of the well known uni-directionally conductin characteristic of the thermionic ampli or connected therein. The telephone station of line 2 may, therefore, carry on two-way communication over composited line 1 without interference from the high frequency carrier currents.

Turning now to the high frequency circuits, 6 represents a thermionic oscillator which produces oscillations of base or control frequency, for example, 5000 cycles. Oscillator 6 overloads a thermionic re ater '7 connected to it by supplying to t e in- 7 will accordingly be of non-sinusoida wave form and are, therefore, the equivalent of a base frequency current of sinusoidal wave form and a series of currents of frequencies which are multiples of the base frequency, that is, harmonic frequencies. The repeater 7 will hereinafter be termed a harmonic producer. The output circuit of hermonic producer 7 is provided with a plurality of tuned selecting circuits 8, 9, and 10 each comprising a tuned path bridged across the output circuit and a similar] tuned loop inductively related thereto. gelecting circuits 8 select currents of the base frequency and supply them throu h an amplifier and a filter 11 to outgoing c annel 5 and thence to line 1. Filter 11 is of the Campbell type and freely transmits oscillations of the base frequency, while substantially extinguishing currents of frequency appreciably differing therefrom. It therefore assists in preventing the transmission of harmonic frequency currents from the harmonic roducer to channel 5 and it serves to exc ude the harmonic producer circuits.

lid

Selecting circuits 9 select currents of a particular harmonic as, for example, 15,000 cycles and apply them as a carrier wave to circuit 12. In a similar manner, circuit 10 selects current of a different harmonic fre- %1]i1ency and transmits it to circuit 13..

ere may be as many of such selecting circuits each selecting a different carrier wave as is'desired, depending merely upon the number of different frequency carrier waves which are to be used.

A signal line 14 of the usual t pe, illustrated in the drawing as a telep one line has terminal connections similar to those oi line 2 with its repeater 3. However, the circuits 15 and 16 associated with line it are not repeater circuits in the sense that they serve merely to transfer speech currents to and from line 14. The function of circuit 15 is to modulate carrier frequency oscillations in accordance with the currents transmitted from the telephone station of line It and to transmit such modulated carrier freuency oscillations to outgoing channel 5. he function of circuit'16 is to select from incoming channel 4, the particular modulated carrier waves which carry the return communication from the communicating station at the opposite terminal of line 1 and to cause these selected modulated waves to reproduce in line 14, speech current by which they were modulated. Circuit 15 includes a balanced modulator M of the type disclosed in United States Patent No. 1,343,306 and a band filter 18 of the Campbell type, connected in tandem. Speech frequenc currents are applied from line 14 to the ivided input circuit of modulator M and carrier frequency oscillations are applied by circuit 12 to the potentiometer 17 1n the common input path of the modulator. As is well known, a modulator of this type will repeat no carrier current from circuit 12 in its input circuit, except at such times as an electromotive force is .a plied across its divided input circuit w en it will re at the carrier currents in its output circuits with a magnitude directly proportional to the amplitude of the wave applied to the divided' input circuit. The Campbell wave filter 18 transmits currents of a band fre-. quency which ma ran e either up or down or both up and own rom the carrier frequency by the essential speech frequenc range which has been previously state Filter 18 serves to define, as desired, the range of the band transmitted to prevent low frequency currents from being repeated from line 14 throughthe modulator M to channel 5 and to exclude from the out ut circuit of the, modulator, the foreign re quency currents of channel 5 which mi ht otherwise enter into its modulating action and produce cross-talk at some receiving station.

Circuit 16 includes a band filter 19 similar to 18, a balanced detector or demodulator D, a thermionic amplifier and a low pass filter20 similar in electrical characteristic to the low pass filter of repeater 3. Filter 19 selects from incoming channel 4, the modulated oscillations of a particular carrier frequency and applies them across the divided input circuit of balanced detector D. The common path of the output circuit of detector D includes a space current source and achoke coil in series. Shunted around the source and choke coil, is an alternating current path comprising 'a capacity element and a potentiometer. Across the potentiometer, reinforcing oscillations of the carrier trequency are applied by circuit 12, it being understood that the carrier frequncy of the modulated wave received by filter 19 is the same as that of the modulated wave trans mitted out to channel 5 by filter 18. The effect of the reinforcing oscillations is both to supply the unmodulated carrier component necessary for demodulation of the received modulated wave components, and to augment the resulting low frequency signal current which detector D supplies to the amplifier. Filter 20 prevents transmisson of high frequency currents to line 14.

There may, of course,-be any number of lines similar to line 14 and each may be connected to line 1 by circuits similar to those of'line 14: but diderin principally in that they are each desi e to operate with an individual carrier requency wave. It will also be clear that line 1 serves to transmit ordinary speech currents from line 2, base frequency oscillations from the harmonic producer 7 and modulated carrier waves for each of the lines 14.

Referring to Fig. 2, the opposite terminal of composited line 1 is illustrated as connected across a single distributing channel 21 instead of to incoming and out oing channels, such as 4 and 5 of Fig. 1. owever,,eith,er arrangement may be used at both terminals of line 1.

Connected to channel .21 through a filter similar in characteristics to filter 20, is a telephone signaling line 22 adapted to communicate over the line 1 with line 2. The filter selects incoming speech frequency currents from channel 21 and transmits outgoing speech frequency currents to this channel.

A filter 23, similar to filter 11,-selects from channel 21, base frequency oscillations and transmits them to an amplifier 24 b which a harmonic reproducer 25, similar in function and o cration to harmonic producer 7, is overloa ed; The selecting circuits 26 which separate the various harmonic frequency carrier waves are series tuned loop circuits and each corresponds in"- the frequency to which it is tuned to a select in their design necessary for the different carrier frequencies involved. Filter 27 is connected to a balancing network through a balanced transformer or hybrid coil with which are associated an incoming circuit 29 and an outgoing circuit 30. Incoming circuit 29 includes a demodulator D having a constant current choke coil in its output circuit and a filter 31 of characteristics similar to those of elements D and 20 respectively in circuit 16 of Fig. 1. Reinforcing oscillations of carrier frequency are supplied to the demodulator by the proper selecting circuit 26 of the harmonic reproducer 25. It follows that filter 31 transmits to line 28, the re roduced signaling currents of line 14. The outgoing circuit 30 includes filters and a balanced modulator M of the type de scribed in connection with circuit 15 of Fi 1. This modulator receives its carrier oscillations from the selectin circuit 26 which sup lies reinforcing oscillations to the demo ulator or detector D of incoming circuit 29. These carrier oscillations are accordingly modulated in accordance with the speech currents of line 28 and are transmitted to line 1.

It will be noted that all of the carrier and reinforcing oscillations at this terminal of line 1 are derived as harmonics of oscillations of base uency transmitted over line 1 from the use-frequency oscillator and its harmonic producer.

The same principles are applicable to radio signaling and to radio teledvnamic transmission generally in so far as the carrier frequency communications are concerned, and if the base frequenc and carrier frequencies are sufficiently igh to be effectively radiated, transmitting and receiving antennae may be substituted in lieu of the line 1.

The term carrier wave. as used herein, includes, not only high frequency oscillations of varying amplitude such as are commonly used in radio telephony, but also high frequency waves or currents either merely interrupted or changed in frequency to denote signal or control impulses. This term is, however, not to be confused with high frequency or radio frequency, since it is possible where ordinary telephony is not being transmitted, to transmit over a conducting line, a large number of different frequency alternating currents ranging from a few cycles per second up toseveral thousand. each of these different frequency currents serving as an individual carrier.

Although the features of this invention have been described as employed in particular circuits, it is to be understood that the invention is not to be limited thereto, but only by the scope of the appended claims.

\Vhat is claimed is:

1. The method of signalling between separated stations which comprises roducing at all of the stations a wave of t e same frequency and of substantially constant amplitude, deriving at each station from the wave produced thereat a wave for the transmission of signals, producing amplitude variations in the wave so derived to represent the signals to be transmitted, deriving at each fiation from the wave produced thereat a wave of constant amplitude, and combining the last mentioned wave at a station with the signal modified wave of the same frequency incoming from another station to reproduce amplified signals.

2. The method of two-way carrier wave transmission between stations associated with a common carrier transmission circuit which comprises reinforcing the waves received at each station by oscillations of the carrier frequency of said waves and deriving all of said carrier waves and said reinforcing oscillations-from oscillations produced by a single source.

3. A two-way carrier wave transmission system comprisin separated stations, means at all of the stations for producing a wave of the same frequency and of substantially constant amplitude, means at each station for deriving from the wave produced thereat a wave for the transmission of signals, means for producing amplitude variations in the wave so derived to represent the signals to be transmitted, means for deriving at each station from the wave produced thereat a wave of constant amplitude, and means for combining the last mentioned wave at a station with the signal modified wave of the same frequency incoming from another station to reproduce amplified signals.

4. The method of two-way carrier signalling comprising modulating in each of a plurality of stations a carrler wave by signals and suppressing transmission of the unmodulated carrier component. transmitting from and receiving at each station the modulation components of the signal-modulated carrier wave, separating the received wave from the wave being transmitted, detecting the receixed wave by combining it with an unmodulated carrier wave of similar characteristics to the wave used at a distant station for modulation, and deriving at a given station the unmodulnted wave for both the modulating and demodulating processes from the same carrier wave source.

5. The method according to claim 2 which comprises deriving a plurality of different impressing reinforcing oscillations of the carrier frequency of said received oscillations symmetrically upon said output circuit w ereby said reinforcing oscillations are prevented from being transmitted to said in at circuit or from said output circuit.

A multiplex transmission circuit having a plurality of receiving channels each including an as mmetrically conducting demodulator, an means for supplying locally produced reinforcing oscillations to the out-' put circuit of said demodulator, whereby said reinforcing oscillations are prevented from being transmitted to said transmission circuit.

8. A system of two-way carrier transmission comprising a plurality of stations, means at each of said stations for receiving carrier oscillations, means for reinforcing said received oscillations by local oscillations of the carrier frequency, and means for deriving all of said carrier oscillations and said reinforcing oscillations from a single oscillation source. v

9. A system according to claim 8 comprising means for composlting a plurality of two-way carrier transmissions on acommon transmission circuit.

10. In a two-way carrier telephone system a plurality of stations each havin a transmitting and a receiving circuit and a source of oscillations, said sources of oscillations having the same frequency, means in'the transmittin circuit of each station for modulatingoscillations from the source at'said station in accordance with speech, and means in the receiving circuit of each station for combining speech-modulated carrier waves from another station with oscillations from the source at the station at which saidreceiving circuit is located for producing interaction currents of speech frequency.

11. A transmission line, a receiving channel and a transmitting channel each connected thereto, a common source of oscillations of a single frequency for supplying carrier oscillations to said transmitting channel and reinforcing oscillations to said receiving channel, and means for preventing interac tion of either of said channels upon said source or upon each other.

12. A receiving system comprising means for receiving high frequency oscillations, a demodulator consisting of two three-element electric discharge devices having separate input and output circuits and havingtheir input circuits oppositely connected to said means, a transmission circuit, said discharge devices having output circuits oppositely connected to said transmission circuit, and means for impressing high frequency reinforcing oscillations on said output circuits.

13. In a carrier telephone system having stations, sources of carrier oscillations of the same frequency at respective stations, means at each station for modulating oscillations from the respective source by'voice control for transmission, means at each station for combining oscillations from the source at the respective station with the incomin voice modulated signal oscillation from t e other station, and means responsive to the combined oscillations for receivlng the detected voice messa e.

In witness whereo I hereunto subscribe my name this 27th day of September A. D.,

EDWARD O. SCRIVEN.

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