US1413357A - Electrical transmission system - Google Patents

Description

P. A. RAIBOURN.

ELECTRICAL Tnmsxusslow SYSTEM.

APPLICATIO'L :zLED {KC 29,1921

1,41 8,357. ente Apr. 18, 1922.

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UNITED STATES PATENT OFFICE.

PAUL A. RAIIBOURN, OF NEW YORK, N. Y., ASSIGNOR TO ELECTRIC COM- PANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

ELECTRICAL TRANSMISSION SYSTEM.

Specification of Letters Patent. Patented Apr. 18, 1922.

Application filed December 29, 1920. Serial No. 433,764.

To aZZwhom it may concern. 4

Be it known that I, PAUL A. RAIBOURN, a citizen of the United States, residing at New York, in the county of New York, State of New York, have invented certain new and useful Improvements in Electrical Transmission Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to electrical transmission system and more particularly to amplifying repeating devices for signaling.

In signaling and other electrical transmission systems, it is, often necessary to associate magnetic devices with the transmission lin at points widely separated or. where the amplitudes of the current on the line are widely different. The losses which a magnetic device in a line or transmission circult causes are dependent among other things, upon the amplitude of the current or energy load traversing the line at that point. Particula'rly is this true at signal repeater stations where the outgoing current may be many times that of the incoming current. It follows that the losses in a magnetic device in the incoming circuit of a repeater and those in a similar magnetic device in the outgoing circuit of the same repeater are of a different magnitude. Since certain other factors involved in these losses and,

particularly, magnetic hysteresis of the core,

increase rapidly with increasing load, it is possible by varying the characteristics of the magnetic device in the output circuit to counteract the tendency which the hysteresis loss has to greatly increase the total loss. The present invention relates particularly to arrangements of this character.

In carrier current signaling systems, as is well known, the transmitted energy is in the form of periodic waves or oscillations modified or modulated in accordance with the signals to be transmitted. For multiplex operation, a plurality of such waves each of a distlnctive frequency and representing an individual message may be transmitted simultaneously over the same line. When, due to the inherent attenuation of the line and its associated apparatus, it becomes necessary to amplify these oscillations, it is possible to select each set of oscillations representing an individual message and amplify each set separately but in the case of a large number of simultaneous systems this results in complicated and expensive arrangements.

If the various transmissions are simultaneously emplified in a single amplifier, there is a tendency for inte-rmodulation to occur, especially where, as in the case of the ordinary three element th'ermionic device, the amplifying power for one set of oscillation may be changed by simultaneously impressing thereon other oscillations. Even where a single set of oscillations is employed, the amplifier may distort these oscillations to give harmonics thereof thus injuring the quality of the received signal and tending to cause interference with other currents of approximately theseharmonic frequencies.

In general, in a multiplex carrier signaling system, and particularly in the case where high frequency carrier transmissions are composited on an ordinary telephone line itis found advisable to separate the ordinary speech currents and the carrier currents before amplification so as to amplify the carrier currents by one two-way repeater and the ordinary telephone currents by another. For this purpose, the well known band filter disclosed in the patent to Campbell No. 1,227,113, March 22, 1917, or an arrangement of the same general character may be used.

Filters of this type consist in general of a plurality of recurring sections having series and shunt reactances designed, according to well known laws, for the range of frequencies of the currents which the filters are to transmit.

According to the present invention, the amplifier may be interposed. between two portions of a filter so that part of the filter sections are connected to the input circuit of the amplifier and the remainder of the sections are connected to its output circuit. All the sections cooperate to selectively transmit currents of a desired range of frequencies to the exclusion of currents of other frequencies. The sections associated with the output circuit perform the additional function of eliminating currents outside the transmission frequency band which originate in the repeater or amplifier itself inconsequence of distortion of waves transmitted thereby or of inte-rmodulation of simultaneously applied waves. Since the output sections transmit amplified energy their load is much greater than that of the input sections and the magnetic cores of the type most economical for the input section inductances are not economical for the out-put section inductances. An important feature of this invention consists in the use of cores of different types for the input and output section inductances, as for example, so called soft cores for the input section inductances and hard cores for the output section inductance thus providing an arrangement of hi h transmission efficiency.

he drawing illustrates diagrammatically, a two way amplifying repeater arrangement connecting two line sections of a transmission line. The circuit arrangement illustrated is particularly adapted for multiplex carrier wave transmission in which a plurality of modified different frequency carrier waves each representing an individual message may be simultaneously transmitted. Each line section is provided with a balancing network N Y which simulates the characteristic impedance of its associated section for currents of each of the frequencies transmitted thereover. Each line section is connected to the two one-way channels 8 and 4 of the repeater by a balanced hybrid coil 1 of the usual type. The direction of transmission over the channels is indicated by arrows.

The arrangement of the balancing network with the balanced hybrid coil as is well known serves to very largely suppress any tendency of the repeater to sing by reason of currents traversing one channel being supplied to the other channel and from it back to the first. WVhere such exact balance is difficult to secure, a less exact balance may be successfully used if the transmissions in the two directions are obtained by currents of different frequency ranges. For example, line section may supply only currents of frequencies higher than 7000 cycles to section E, and section E in turn may transmit only currents of frequencies lower than 7000 cycles to section lV. In such an arrangement the two chaimels of the repeater may each be equipped with a filter to suppress currents of the frequencies transmitted by the other channel. thus effectively preventing singing. The two channels are therefore alike except for the filtering arrangements.

Each channel includes an amplifier, preferably of the highly evacuated three element electron discharge type, for amplifying the currents supplied to that channel. In order to secure faithful repetition, these amplifiers and their circuits are so designed as to produce as little intermodulation or other distortion of the different frequency currents as possible. A certain amount of intermodulation is inevitable particularly where large gains are desired and where the repeater is subject to large variations of supplied electromotive force. If, for example, currents of 3500 and 4500 cycles frequency, respectively, are being simultaneously transmitted from section E to section WV, any intermodulation resulting from the action of the amplifier will produce a sum frequency component current of 8000 cycles. balancing of the hybrid coil 1 would permit this current to be fed back over the other channel 3 to the section E to cause serious interference or cross talk in the 8000 cycle receiving channel connected at the remote end of section E. In a similar manner the repeater of the other channel might produce troublesome difference frequency components. To eliminate such harmonics and intermodulation currents, the filter for each channel is separated into two units, an input unit F and an output unit F and the amplifier is inserted between these units. Both units F and F of one channel serve to prevent transmission of currents of the frequencies assigned to the other channel which are impressed upon unit F A because of the unbalancing of the conjugate connections or of other characteristics of the line. Unit F serves in addition to suppress harmonics and intermodulation currents produced by the repeater which are of frequency outside the normal range of its channel.

The filter units of channel 3 which repeats current of frequencies above 7000 cycles from section V to section E are of the high pass type and each consists of similar sections having series capacity and shunt inductance. These units serve to transmit currents of frequencies higher than 7000 cycles with substantially negligible attenuation and to suppress currents of frequencies below the cut-off frequency of 7000 cycles. The units of channel 4 are of the low pass type and consist of recurring sections having series inductance and shunt capacity. These low pass filters transmit currents below' the cut-off frequency of 7000 cycles and suppress those of higher frequency. The invention is not limited to the particular type of filter disclosed.

Each filter F is required to transmit currents of greater amplitude than those traversing the corresponding unit F because of the amplifying action of the repeatertubes. The inductances of unit F are therefore subjected to much larger currents and there is a consequent tendency for greater core losses. In particular there is a tendency for much larger hysteresis loss. It is 'possible to decrease the permeability of the cores and thus to counteract to some extent the tendency of increase of the hysteresis loss. This may increase certain of the other core losses, but the net result will be a smaller total core loss than would be had for the same value of current with cores of the character used in unit F This may be Any unaccomplished in various ways. One expedient which has proven successful consists in providing the inductance coils of unit F with cores of the soft core type disclosed in Patent #1,286,965, issued December 10, 1918 to G. W. Elmen and the coils of units F with cores of the hard core type disclosed in Patent #1,297,126 issued March 11, 1919, to the same patentee. The cores of the F inductance coils are preferably composed of annealed finely divided electromagnetic iron with insulating material, for example, a coat of red iron oxide separating the particles, the whole being compressed into a self-sustaining solid of specific gravity, approximately 7 The cores of the F inductance coils are similarly constructed with the exception that with the annealed iron particles are mixed unannealed iron particles thus decreasing the magnetic retentivity and the hysteresis loss. The two units accordingly operate with comparable efiiciencies-at very different loads, since the F unit coil is of considerably higher efliciency at the large currents which it must handle than the F unit.

It is also possible to use so called core coils for the unit F An equalizer indicated at 5 and consisting of a resistance shunted by a capacity and inductance in series, serves to so terminate the F A unit as to equalize the difi'erences of line attenuations at the different carrier frequencies used, thus giving outputs from the repeater of substantially equal value for the several frequency channels.

The broad principle ,of the invention is not limited to carrier operation but is applicable wherever the volumes of transmission through similar magnetic elements of a transmission line are widely different. It is therefore to be understood that the S00 e of the invention is to be limited only by t e appended claims.

What is claimed is:

1. In combination, an electricaltransmission system, two magnetic devices associated therewith, the volumes of transmission at the portions of said system associated with said devices being widely different, said magnetic devices havingdifierent magnetic loss characteristics whereby said devices operate at comparable efficiencies under their respective normal loads.

2. In combination, an amplifier having an incoming circuit and an outgoing circuit, a coil associated with said incoming circuit and a similar coil associated with said outgoing circuit, said coils having cores of different magnetic characteristics whereby the air transmission efiiciencies of the two coils at their respective normal loads are comparable.

3. In combination, a wave filter having a plurality of recurring sections and an amplifier dividing said sections into two groups, the sections of one group having higher transmission efiiciency than those of the other for the same load.

4. In combination, an electric wave filter comprising two groups of recurring sections, an amplifying device having an input circuit connected to the first of said groups and an output circuit connected to the second group, the second group having higher transmission efficiency for amplified currents than the first group.

5. A repeating device having an input circuit and an output circuit, a line connected to said input circuit for simultaneously applying thereto a plurality of different frequency currents each of which represents an individual message, filtering means connected to the input circuit of said repeating device for excluding therefrom currents outside a desired frequency range and a second filtering means connected to the output circuit of said repeating device for suppressing 112111101110 or combination frequency currents produced by said device and of frequency outside said desired range, said two filtering means having the same order of transmission loss at their respective loads.

6. A carrier telegraph repeater comprising a channel for repeating in one direction currents of one range of frequencies and a channel for repeating in the other direction a band of currents outside of said range of frequencies, each channel comprising a band filter consisting of two groups of recurring sections and an amplifier electrically interposed between said groups. the output group of said channel having a higher transmission efliciency for large currents than said input group.

7. In combination, a band filter having a plurality of recurring sections each including an inductance having a magnetic core, an amplifier dividing said sect-ions into two groups, the inductance cores of one group consisting of finely divided annealed magnetic particles and the cores of the other grou consisting of a mixture of finely divide annealed and unannealed magnetic particles.

In witness whereof, I hereunto subscribe my name this 28th day of December A. D., 1920.

PAUL A. RAIBOURN.

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