US1819054A - Carrier signaling system - Google Patents

Description

Aug. 18, 1931. H A, AFFEL 1,819,054

CARRIER SIGNALING SYSTEM Filed May 2 4, 1927 ave Vallone P ae Lais zlvzlradared @maz/fil@ y Sendai/zg of Subset Metwnrk ATTORNEY Patented Aug. 18, 1931 vunirse stares ear-snr ferries f HERMAN A. Arret, or Rinenwoon, new JERSEY, Assienoa To' AMERICAN TELE,-`

PHONE AND TELEGRAPH COMPANY, A OOBPOBATIGN OF NEW YORK CARRIER SIGNALING SYSTEM Application `filed 'May 24,

This invention relates to signal transmission systems, and particularly to a method of operating such systems to minimize the effect of noise upon the signal wave being ,5 transmitted, the said method being characterized by an intentional predistortion of the signal wave, and therestoration to its normal form after its transmission over or through a medium. The inventionkmay be applied to voice frequency transmission systems andto carrieror radio systems.

In the transmission of signals over a signal transmission system, such as carrier or radio system, it is desirable, in order to avoid distortion, that the system shall have'the same over-all equivalent at all frequencies within the range to be transmitted. In the systems heretofore employed, van effort has been made to provide in each part of the sys- 201cm, including'the parts subject to external sources of noise, substantiallyV distortionless transmission of the frequencies in the signalingwave. lt is well known that under normal conditionssome of the frequencies inthe original signal wave contain larger amounts of energy than others, and that the energyfrequency.distribution may be. further dis*- torted duringl the conversion in the transmitter from iair wavesinto electrical waves. In the, ordinary transmission system the nonuniform distribution thus obtained in the transmitteris preserved to a greater or'less extent throughout the system. i

This vinvention resides in a method of operating a. signal transmission system, which consists in predistorting the signa-l wave at the transmitting end-in such a manner as to ensureA a practically/constant amplitude for all frequencies inthe signaling wave and in' 40 restoring' the transmitted wave to its original format the receiving station by a distortion that is the complement of the distortion at the transmitting station.

' ln `a transmission circuit involving a sende ing terminal, a line or transmission circuit, and a receiving terminal, there are often one er more points at which gain is introduced inthe circuit, usually by means of vacuum tube amplifiers, which, of course, have a deli- 5o nite load-carrying capacity.- Also, those cir- 1927. Serial No.`193,902.

cuits areinvariably affected Vby noise from external sources. Such a circuit is usually arra. ed so that the ampliiication introduced in the circuit will maintain the transmission level suiliciently high 'to override such noise. l have found that in such a circuit the energy levels may be better distributed and the eiective carrying capacityr of the amplifier more efficiently employed,fwith less over-all interfere-nce, if there is provided at the sending end of th-e circuit a certain transmission-frequency distortion, and similarlyv at thereeiving` terminal a complementary `frequency distort-ion, both `properly related to the volnine-frequency characteristic of the transmitting source and `the noise-,frequency characteristicof the disturbance. The invention will be clearly understood from the following description when readin connection with the attached drawings, of which Figure l showsjschematically a voicefrequency circuit embodying the invention; .Figs la, 17), lc and 1d are graphs illustrating themethod fin which the `invention is embodied; Fig. 2 represents schematically a radio circuit embodying*- the invention, and Fics. 2a, 2b, 2c and 2d aregraphs illustrating the application ofthe invention in' Fig. 2. .In Fie. 1 atterminal A, the transmitter l together with a substationY set 2, (consisting of the ordinary substation apparatus, repeating coils, etc.) represents a. transmitting source of speech frequency signals. The output of the set 2 after being `transmitted through the subscribers loop is connected with the distortionv network 3 'having the characteristic shown in Fig. 1b, the nature of which will be fully explained hereinafter. rlhe output side of the network is connected with theY amplifier li, which in turn is connected with the line circuit 5, havingtherein a plurality of ampliiiers such as 6 and 7, the purpose of which is to maintainthe level of the trausmi ted signal well above the noise level of the line, thereby rendering the signal free from interference due to the noise. lThe' line circuit 5 is connected at the receiv- .ingterminal B with the amplier `8, kwhich in turn is connected witha `distortion network E), the characteristic ofV which,-as shown in Fig. 1d, is complementary to that of network 3. The output of the network 9 is connected with a substation set 10 for the detection of the signal which is impressed upon the receiver 11. The arrangement, representing a one-way circuit, has beenV used for the purpose of simplifying the description of the invention, but it is, of course, to be understood that two way signaling may be effected by well-known means.

The manner in which the system operates in order to insure the same over-all equivalent at all frequencies is as' follows: As stated hereinbefore, the volume-frequency characteristic of the subset 2 is as shown in Fig. 1a. This characteristic shows that the maximum volume of energy is in the neighborhood of 1,000 cycles. Furthermore, let it be assumed that the noise-producing interference has a substantially uniform distribution of energy with respect to frequency. I have found that by introducing a loss varying with frequency such as lis shown in Fig.

1b, 'the output of the amplifier 4 to the line willbe substantially constant for all frequencies within the desired range, sucli, for example, as that of speech. This loss may be produced by a network 3 having the char-V acteristic shown in Fig. 1b. As the curve shows, the network producesV the maximum 'lossat 1,000 cycles, and for frequencies high- `er or lower than that frequency, the loss will vary with frequency in proportion to the changes in volume', as shown in Fig. 1. relative volume transmitted to the line, as shown in Fig. 10, will be substantially constant, and the line ampliers will be loaded to the maximumr extent at all times. The frequencies remote from the point of maximum subset output will be maintained at a higher level than is practicable if the circuit is operated in the usual manner with the maximum levels limited by the carrying 'capacity of the repeaters for a. relatively narrow frequency range, such as that in the neighborhood of 1,000 cycles. Y At the receiving end of such a circuit, a complementary distortion must be introduced in order to restore the transmitted signal to its original form. This is effected by a network 9 having a Aloss-frequency characteristic, such as is represented by Fig. 1d. An inspection of this figure shows a minimum loss in the neighborhood of 1,000 cycles,

and greater loss for frequencies above and below that frequency. It -will therefore be apparent that the energY impressed by the amplifier S on the network 9 will be transmitted through the latter with the various frequencies having losses represented by the characteristic 1d, so that the resultant wave impressed upon the subset 10 and detected lthereby will Yhave the characteristic shown in Fig. 1a', which is the characteristic of the transmitted signal.

The arrangement shown would also be apessary aparatus for modulation, demodulation, etc.

rIhe arrangement shown in Fig. 2 illustrates the application of the invention to a radio transmission system. In this figure, the transmitter 1 at terminal A forms part Vof a substation set 2, the output of which is connected with a distortion network 3, which in turn is connected with a radio frequency transmitter 12. In this case, the transmitter isassumed to be of the high-quality type, 'producing substantially no distortion in the air waves comprising its input. The output of this transmitter is connected with the antenna 13, which radiates the high frequency signal to a receivingantenna 14 assocated with the terminal B. At this station, the antenna. 14 is connectedwith a radio receiver 15, the output of which is connected with the subset 10, the connection including a distortion network 9. The output of the subset is connected with the receiver 11. In the system illustrated, the relative energy distribution at various frequencies of speech may be as represented in Qa., wherein it will be seen .that the maximum energy is in the lower frequencies. Byv the use of a network 3 having the loss-frequency characteristic shown in Fig. QZ), the relative volume of the transmitter output will besubstantially constant forall the transmittedfrequencies, as shown in Fig. Qc, At the receiving terminal, the received energy is detected and impressed upon the network j9 which has a loss. frequency characteristic as shown in Fig. 2d. As this ligure shows, the greatest loss is throughout the higher frequency range. The result, therefore, is that the energy impressed upon the network will be modified thereby, and the resultant wave impressed by the subset 10 uio rio

of course, that it is capable of embodiment in other and different forms Without departing from the spirit and scope of the appended claims.

What is claimed is:

1. The method of transmission which consists in distorting the signal Wave in order to obtain approximately the same level for 'all frequencies Within said Wave and introducing a compensating distortion at the receiving end.

2. In a transmission system, the combination With a translating device having a definite load limit, of means `for distorting the signal Wave to be impressed upon said device in order to bring the level of each frequency of said Wave up to the maximum level for the apparatus included in the system.

3. In a signal transmission system the combination with a transmittingstation of a receiving station, a medium connecting the said stations, the said transmitting station comprising means to create a signal, and means to distort the said signal to ensure a practically uniform amplitude for all frequencies present in the said signal, and the said receiving station comprising means to introduce a complementary distortion in the received signal impulse to restore. the impulse to the same form possessed by it prior totransmission.

4. In a signal transmission system the combination With a source of energy the volume of which varies with frequency, of a tiansmission medium over which the energy is to be transmitted, an amplifier connected between the said source and the said medium, a distorting network connected between the said source and the said amplifier to introduce a loss in the transmitted energy, which loss varies With frequency dir-ectly with the variations in volume as created by the said source, another distorting network also connected with the said medium to introduce a loss in the energy as received, which loss ,fvaries With frequency inversely with the variations o-f the loss produced by the said first mentioned distorting network, thereby restoring to the said energy the Wave form possessed by it at the saidsou'rce.

5. The method for maintaining the overall transmission equivalent of'a signal circuit substantially the same for all frequencies Within the range transmitted, which consists in distorting the signal prior to transmission so that the volume of energy for each frequency will be the same, transmitting the signal as thus distorted, and distorting at the receiving end of the system by introducing such losses as are necessary to restore the signal energy to the form possessed by it prior to its distortion before transmission.

6. The method for maintaining the overal] transmission equivalent of a signal circuit substantially the same for all frequencies Within the range transmitted, Which consists yquency in 'distorting the? si gnat priorlto .transmission sefthatithe volume v ofV energy for `eachy freivillf ybe the same, V introducing a loss into theY circ-uit atitstra-nsmittiiigeiid, which loss varies withy frequencyL directly With the variati'oiioffthe' voluine of energy :with v.frei quency, amplifying and transmitting tliesig- `n-al thus modified, receiving thesignal and introducing afloss into tliesaid Vcircuit atthe receiving rend, )vliich loss varies yWith frey quency inyerselyivitli' the corresponding loss variations at the transmitting end of the said circuit.

7. The method for maintainingthe over-all transmission equivalent of a signal circuit substantially the saine for all frequencies Within the range transmitted, Which consists in creating a signal comprising a band of frequencies, the volume of energy of which Y restored to the form possessed by it at its creation, and detecting the signal as thus restored. y

8. in an electrical transmission system, the

combination with a translating device liavin@` a fixed load limit, of a source of oscillatons connected with said device, capable of simultaneously producing a plurality of fre-A quencies, and means interposed between said device ann said source to substantially equalize the energy level of all frequencies iinpressed by the source upon said device.

9. In an electrical transmission system, the combination with a transmission circuit for transmitting electrical Waves having therein a translating device through which electrical energy may be passed at a fixed level Without distortion of the electrical Waves, of a source ofoscillations of a plurality of frequencies andmeans connecting said source to the said transmission circuit to substantially equalize the energy level of the oscillations applied by the source to the transmission circuit.

l0. rlfhe method of operating an electrical transmission system having therein a device havin@- a fixed load limit, Which consists in generacing oscillations of a plurality of frequencies, equalizing the energy level of said oscillations and simultaneously impressing upon a transmission circuit the oscillations of all frequencies as thus equalized for transmission thereover.

l1. The method of operating an electrical transmission svstem having therein a translating device having a fixed limit for the ieo transfer of energy Without distortion, which consists in creating a signaling Wave containing a plurality of frequencies, equalizing the energy level of all frequencies of said'wave, and impressing the frequencies as thus equalized upon the translating device for transmission over said system.

In testimony whereof, I have signed my name to this specification this 23rd day of May, 1927.

HERMAN A. AFF EL.

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