US1677966A - Carrier signaling system - Google Patents

Description

E. l. GREEN CARRIER SIGNALING SYSTEM I July 24, 1928.

Filed Deo. 3Q, 1925 A TTORNE Y 1%. SQSM mg Patented `July 24,` 1.928.-

lUNITED STATES PATENT OFFICE.:

'ESTILL I. GREEN, OF EAST ORANGE, NEW JERSEY, ASSIG-'NOR 4'10 AMERICAN TELE- PHONE ANI) TELEGBAPH COMPANY, A CORPORATION OF NEW YORK.

Calmann SIGNALING SYSTEM;

'- Application nica December so, 192s. semi iro.- 78,455.

the lowest frequency channel (which has the least attenuation) below the overload point of the repeaters. This equalization of the yavious channels is ordinarily carried out by means of networks which reduce all channels to the same level at each repeater point. This practice of reducing t-he volumes of all the channels to substantially the saine level, which in practice is the level ofvthe'highest frequency channel, is highly ineiicient because of the waste of energy of the lower frequency channels.

This invention resides in a method and means for equalizing the transmission equivalents of a plurality of channels of different frequencies transmitted over or through `a common transmitting medium, which method consists in inverting the channel fre quencies in alternate repeater'sections.` Such,

. method has distinct advantages over. the

Vfinethod heretofore employed in that the present method equalizes the channels with respect to their frequency of transmission,

which is the real difference between the channels, rather than with respect to attenu@ ation, which is only a characteristic of the frequency. The equalization of the channels with respect to frequency effectively provides equalization with respect to all the factors whichf are a function of frequency.

such as gain, noise, cross-talk, attenuation variations and other similar functions This invention will be clearly understood from the following description when read in connection with the attached drawing of which Fig; 1. shows schematically a form of embodiment of the invention -in which the range of frequencies to be transmitted over the common medium 'is such asto permit the carrying out of the invention bywdividing l' the channels into only two groups; and Fig.

2 shows .schematically an' arrangement `fol' handlinga greater number of groups. 'In

the drawing the line L1, which represents the medium over which a plurality of channels is transmitted, ismade upv of a plurality of sections designated X, Y and Z, -thc ad]acent sections being connected throufh the repeaters, such as Nos. 1 and 2, and tie said,line being terminated at its ends by a ool station, such'as A. While station A is represented as beingr adapted onlyfor the transmission of signals, it is to be understood, of course, that it may be readily adapted both for transmission and-reception in a manner` that is well understood by those familiar with the art. Station A com rises a'pluiality of branch circuits of whic sirare shown in the drawing, but the number may vary depending upon the' number of channels of communication. VEach of the branch circuits comprises a transmitter, a's indicated by 7 to 12, asource of carrier oscillations, asindicated by 13 to 18, a modulating device, as

indicated by 19 to 24, and a filter, such as is indicated by 25 to 30, The transmitters 7 to 12 may be any device by means of which a-modulating current is impressed .upon the input side of the modulators'to modulate the carrier current from the oscillators. Each oscillator is designed` and adjusted to produce a frequency differing from that of the other oscillators. Y

Considering, lfor example, branch circuit N o. 1, if the transmit-ter 7 is designed to impress a frequency range from z ero to 4 kilocycles upon the input side of the modulator 19 and the oscillator is adjusted to produce kilocycles,the output of the modulator (assuming that it were of the` type to suppress the carrier frequency) would comprise two bands, one ranging from 100 to 104 kilo- 'cycles and the lother ranging. from 100 to 96- kilocycles. Assuming single side band transmission, the filter 25 would be 'adjusted to pass only one band, as, for example,that

representing 100 to 104 kilocycles. In like manner, each of the otherv branch circuits would produce a band of oscillations based.

upon its individual carrier frequency. Thus circuit No. 2 would produce the` band 105 to 109-kilocvcles, and the'third'circuit a band 11o to iii kiiocyeis. Circuits 4 tez/6, in-

clusive, would produce three channels'ranging from 116to' 130 kilocycles. f .Y All of these frequencies would be impressed juponY the line L, and transmitted m to the repeater No. 1, which comprisesy the filters 31 and 32, the former passing the frequencies 100 to 114 kilocycles, and the latter the frequencies 116` to 130 kilocycles.

-These filters are connected with the input 36 and 37, respectively. The output circuits aol of the amplifiers are connected with thel section Y of the line which extends to repeater No.J 2. This repeater is preferably similar to repeater No. 1,' and upon the drawing the same parts have at repeater No. 2 been givencthe same numerals primed.

.Repeater No. 2 is connected with section Z of the line, which may extend to another. repeater or to a terminal station having a plurality of branch circuits, such as A, adapted to receive the channels and to demodulate the frequencies and produce the signal freqency upon each channel. n .n

The principle involved in this invention yconsists in splitting up the n channels into groups at each repeater station and modulating each group by a carrierv frequency equal to the sum of the maximum and the mini mum transmitted frequencies. This will be made clear by vconsidering a specific case, such as that involved in the transmission of six channels, representing a frequency range of from'lOO to 130 kilocycles. These frequencies,'which are impressed upon section X of the line, will be attenuated as the result'of such transmission, the higher frequencies, of course, suffering greater attenuation than the lower frequencies. It will there ore be apparent that if at the repeater station No. 1 these frequencies lare inverted before transmission over sectionl Y of thel line,'the frequencies having greatest attenuation in section X will have least attenua'' tion in's'ection Y, and vice versa.. This desirable result is effected in the following manner:

4 The frequencies which are present in the channels ofl transmission are ,divided at repeater No. 1 into two groups by means of the filters 31 and 32. Thus filter 31 transmits'through it the frequencies of 100 to 114:

kilocycles, representing channels 1 to 3, and

filter 32 transmitsv frequencies. 116 to 130 kilocycles, representing channels @to 6, If the intermodulation between frequencies of a group is .not'.serious,' it will always be possible to effect the inversion of .the frequencies by employing only two groups at each repeater. In case the intermodulation cannot `be neglected, the groups must be so 'chosenthat 4the intermodulation frequencies of any group `fall outside thatl group and lowest frequency and f2 4the. highest frequency present in the line L1, inversion of the frequencies may be effected without interinodulation if 2f1 is equal to or greater than f2. Vhere this condition does not hold, it might be necessary to first divide the channels into ,two groups and subsequently divide these groups into smaller groups until such into two groups, 4as shown in the drawing.`

If these -groups be'beaten with the same carrier frequency which is equal `to the sum v of the lowest frequency in any group and the highestfrequency in any group, and the difference frequency is selected from each beating operation, it will be found that the frequencies of the channel have been inverted. Thus when .the group representing 100 to 111,4 kilocycles, which may be termed the low frequency group in the line sect-ion X, is beaten with 230 kilocycles, the difference frequencies, namely the group represented by 116 to 130 kilocycles, are the same as the higher frequencies transmitted over the section X,'and. in like manner, when the group represented by 11G to 130 kilocycles is beaten with 230 kilocycles andthe differ-- ence frequencies are selected, the resultant frequencies, namely, 110 to 114 kilocycles, are the same as the frequencies of the lowest channels `transmitted over section X. In

other words, the repeater has inverted the frequenciesof the channels. These frequencies are given the required amount of am plification by 38 and 39 and transmitted over section Y to repeater No. 2. At the'latter low frequencies in section X, become high v frequencies in section NY, and in like man` ner channels 4 to 6, which are of relatively high frequencies in "section X, become low frequencies in section Y.l By means of this frequency translat-ionl or inversion in a plurality of sections of the line, the equivalents of the various channels may be made sub- .lis

stantially the same.' With the frequency asl l sumed'in the foregoing instance no interference-will be produced bythe intermodulation of the frequencies`, `so that the inver-- sion'may be cared for by a single division of the channels into two groups. If, however, y the frequencies-of the channels ranged, for

example, from 60 to 130kiloeyeles, it wouldV the inverted group. j, represents. the be necessary to-employ a greater number of 130` dividing processes to prevent intermodulation, such as is shown schematically in Fig. 2. In such system' the line L, would be connected at repeater`1 with two branches lhaving filters 41 and 42 capable of dividing the entire range of frequencies .into two groups,one extending from 60 to 94 kilocycles, and the other from 96 to 130 kilo-l cycles. Since in the first group the frequency is more than half of 94, the inversion of this group may be effected by dividing the group into two sub-groups, by means of the filters 43 and44 the former of which passes the frequencies between 60 and 7 tkilocycles andthe latter the frequencies between 78 and 94 kiloc'ycles. Since the lowest frequency of all the channels being transmitted over the system is l6() kilocyclesfandl the highest is 130 kilocycles the beating 'frequency', employed is the sum of those fre-- quencies. namely, 190l kilocycles. This is 'provided by an -oscillator 47 which is connected with `the several branchcircuitsthrough filters or circuits tuned to the beating frequency which permit-s the` passage of the beating vfrequency to the branch circuits butv prevents interaction between thosev circuits. The channels between 60 and 76 kilocycles pass through the modulator 49 together with the beating frequency of 190 kilocycles, and the difference frequencies resulting from modulation, which range from 130 tol14 kilocycles, are passed by the filter `51, amplified by the amplifier 53, and are passed to the line section Y. In like manner, the. group of frequencies extending from 78 to 94 kilocycles will T be beaten with 190 kilocycles in the modulator 50, and the difference frequencies, namely, those extending' from 112 to kilocycles, will be passed bythe filter amplified by the amplifier 54. vand passed to fthe line. It will be seen that the group of frequencies that was lowest in the frequency scale of all, the frequencies transmitted over vthe line section X now occupies the highest position in the frequency scale. Similarly thegroup ranging from 7 8 to 94 kilocycles, which wasnext to the lowest. in transmission over section X, nowv voccupies the positionnext t'o the highest in the frequency scale in transmission over secy tion Y. In like manner the group of frequencies ranging from 96 to 130kilocyc1es, which is passed by the filter 42,1is subdivided into two groups bythe filters 45 and46-and the frequencies present in eachgroup are beaten with 190 kilocycles supplied by the oscillator 47. The difference frequenciesI resulting from modulation are passed by the filters 57 and 58 and amplified by-amplifiers 59 and 60, respectively. vItwill be seen that the group ranging fromv 114 to 130 kilocycles, passed by the filter 46, has, by the process of modulation and selection, become the vlowest in the frequency scale of all the groups transmitted overy section Y, occupying the Irange from 76 to 60 kilocycle-s. In like manner the group ranging from 9.6 to 112 kilocycles in transmission over section X, ranges from 94 to 78 kilocycles in transmission over section Y.. The selected frequencies will be brought together againv and transmitted over section Y to repeater No. 2 lwherein a similar process would restore the channels to 'the frequencies possessed by them in section X. While'the frequencies assumed for thepurpcse of describing this invention may seem to range fairly high,

such frequencies are not incapable of employment in telephone systems land may be readily employed in carrier communicationv over power circuits. It is, of course, obvious that any frequencies may be employed without exceeding'the scope of the invention.

While this invention has been disclosed as embodied in particularforms, it is ca` quency and -the f equencies in each group,`

and impressing u on the same transmitting medium the resulting frequencies as selected. 2. The method of equalizing transmission of a plurality of carrier channels trans'- .mitted over or throughthe same medium,

which consists in separating by filtering the said channels to form two groups, one consisting of the higher frequencies and the other the lower frequencies, separately beating each group of 'frequencies by the same beating frequency which equals the 4sum of. the lowest frequency and the f highest frequency present in the channels, selecting-the dlference frequencies resulting from reach beating operation, amplifying the selected,A

frequencies in each group, the degree ofamplification of the higher frequencies being greater than thelower frequencies, and re-A combining the frequencies for transmission over`the said medium.

The method of equalizing of a plurality of carrier channels -transmitted over or through the same medium',

transmission p which consists in dividing the channels into two groups, changing the frequencies of the first group into those of the second group, and

vvice versa, by beating separately the fre` quencies in the two groups by afrequency equal to the sum of the lowest and highest frequencies in both groups, amplifying the frequencieslresulting from the beating aopi frequencies of both. groups as thus trans-y lated, and impressing the amplified frequenc1es upon a common transmitting medium.

4. The method .of equalizing transmission separating the said channels into two groups,

by filtering, separately beating the groups of channels by a frequency which equals the' sum of the lowest and the highest frequencies in both groups, selecting the difference erations, separately amplifying to vdifferent degrees each'grou .of selected frequencies, and recombining t e groups as-thus amplified.

5. -The method of equalizing transmission of a plurality of carrier channels trans- 'mitted over or through the same medium,

-which consists in dividing the channels into such a number of groups that the highest4 frequency in any group shall be at least twice as large as the lowest frequency in the said group,'beating the frequencies in two adjacent groups by the sum of the highest and lowest frequencies present inv both groups, selecting the differencel frequencies of the said'beating operation, Iand amplify-V ing the selected frequencies in each group, the degree of amplification being in accordance with the relative position of the said frequencies in the frequency spectrum, and combining the frequencies as-thus amplified.

6. Ina carrier signaling system, the combination with a terminal circuit comprising a plurality of branches, each having a source of carrier current, the frequency of which differs from that-of thel others, a source of.

signaling current to modulate the said carrier, al transmission circuit connected with the vsaidvtermvinal. circuit and common to all of said branches,` and.V a repeater lcomprising two branches each having a filter, a modulatorand an amplifier, and a source of/beating oscillations, the frequency beingl the same for both branches and equal tothe sumar. the lowest frequency and the highest'` frequency present in all channels.

7.T,he,method of equalizing the'transmission' equivalents of a plurality of carrier channels which consists in transmitting a.

plurality of channels of different frequencies, separating the said channels into a plurality of groups, the number of which'will be such that the lowest frequency in any group shall be equal to or greater than half of the highest frequency in that group, separating the channels `in each groupv into two sub-groups and separately beating the channels in eachsub-group with a beating frequency equal to the sum of the lowest and t-he'highest frequency in each vpair of sub-A groups, selecting the difference frequencies resulting from'each beating operation, ameplifying and transmitting the selected fre-4 quencies.

8.l In a carrier signaling-system, the combination with a transmission line of a repeater inserted between sections thereof, a f

source of a plurality of channels connected ywith the said line, said repeater comprising a plurality of branch circuits connected with the said line having mutually exclusive filters, one adapted to pass the lower range of frequencies and the other the higher range,

each branch having a modulator and a filter lconnected with the output thereof,` and a source of beat-ing oscillations connected with the input sides 'of bothl modulators, thefrequency of the'said beating oscillations being equal to the sum of the lowest and the highest frequencies in all channels.

9. In a carrier signaling system, the combination with atransmission line of a repeater inserted between sections thereof, a source of a pluralityof channels connectedl Dwith the said line, saidl repeater comprising a plurality of branch circuits connected with the said line having mutually exclusive filters, one adapted to pass the lower range of frequencies and the other the higher range, each branch having l'a modulator and a filter connected with the output thereof, a source of beating oscillations connected with the input sides of both modulators, the frequency of the said beating oscillations being equal to the sum of the lowest and the highest frequencies in all channels, and means connected with eachlbra'nch circuit to amplify the frequencies transmitted by the respective'flters. l

Iny testimony whereof, I have signed my name to `this specification 'this 29th day of December, 1925.

EsTILL IQ GREEN.

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