US1941116A - Communication system - Google Patents

Description

Dec. 26, 1933. v M. E. STRIEBY COMMUNICATION SYSTEM Filed May 21, 1931 2 Sheets-Sheet l nix 4) I. let 1i 0/ A ,h m Q Q w 1 r V Q m C oi. h T T 3 i hwrwhlii 4 2 ow Q 3 Q on O\\\ INVEN TOP By M E 5 TIP/EB) A T TORNEY Dec. 26, 1933. M. E. STRIEBY COMMUNICATION SYSTEM '2 Sheets-Sheet 2 Filed May 21, 1951 mm Wm M ew u 7 X M w INVEN TOR ME ST/P/EBY By 7 WWW/1 A r TORNE) Patented Dec. 26, 1933 PAT EN T Fri CE? COMMUNICATION SYSTEM Maurice E. Strieby,'Maplewood, N. J., assignor to Bell Telephone Laboratories, Incorporated," New York, N. Y., a corporation of New York Application May 21,1931. Serial No. 538,919 lfi-Claims. (Cl. 178--44) The present invention relates to an electrical system for the transmission of intelligence and more particularly to a system employing carrier waves. l T

It is an object of this invention to increase the flexibility and efliciencyof a carrier wave transmission system, to extend the signaling frequency range, and to reduce the" amount and cost of apparatus required. V h

Asystem in accordance with applicants invention is adapted to the transmission of signaling waves extending over a much wider range of frequencies than it has heretofore been the prac; tice to employ. It is especially adapted to utilize to the fullest extent the characteristics of a transmission line in which one. conductor, essentially.

, over other transmission lines may similarly be,

. is less than a given standard, increased where it pairs.

in the form of a hollow cylinden-serves as. the

return pathfor an inner conductor concentric therewith and separated therefrom by. a suit able dielectric. Patent No. 1,781,124 issued to H. R. Nein on November 11, 1930 discloses a suitable type of line. Such a transmission line is capable of carrying with moderate attenuation waves having frequencies of the cycles per second. V

Applicants system preferably makes use of carrier waves on which signals are impressed by successive processes of modulation. A plurality of signals are first impressed on a corresponding 1 number of carrier waves and applied to a transmission line in a manner well known in the art. At a succeeding point in the systemthese'modulated waves are applied. as a group to'a second carrier wave of higher frequency. Other groups of modulated waves arriving at the same point order of mega applied to the same or to individual carrier waves. The resulting wide band of; carrier wave signals applied to a second transmission line, preferably one of the coaxial conductor type. Two-way transmission may be obtained} as heretofore, either by'using diiierent frequency ranges for the two directions or by using separate conductor The attenuation per unit length of a coaxial conductor transmission line varies approximately as the square root of the frequency and inversely as the inner diameter of the outer conductor.

These factors, together With'the distance between the repeaters, which are inserted atintervals in the transmission line, and the permissible attenuation between repeaters, are closely 'yet flexibly related to each other. Taking advantage of this flexibility, the size of the conductorsmay V be reduced where the distance between repeaters is greater. and varied accordiiigto the maximum frequency to be transmitted.

In a country-wide network embodying applihaps in a lead sheath to form 'a flexible cable such as shown in an application of H. W. Dudley bearing Serial No. 487,153, filed October 8, 1930..

Asnoted above, the small conductors will trans-. mit the entire frequency spectrum used with the large conductor, although much larger attenuation will be encountered and closer spacing of repeaters will be required. Under some conditions it may be best to use. several small coaxial conductor circuits in a cable each of which transmits only apart of the frequency spectrum.

This would require that the frequency range be broken upby suitable apparatus at the terminal of the large conductor, so that the transmission over the small conductors becomes essentially a carrier-on-cable system.

As a concrete illustration, suppose it were desired to bring into an urban district such as New York a thousand-channel system- A coaxial pair,

with a 3 Ai-inch pipe as the outer conductor would serve in'the rural districts to transmit the four and a half million cycle band of frequencies that this might require. In the metropolitan area, however, considerable difficulty would be metin attempting to run a large, inflexible'conductor through the underground network of lines, pipes and other construction to be found beneath many city streets. A flexible coaxial pair of one-half inch diameter within a lead sheath would be much more practicable. This would transmit the en-' tire frequency band, attenuating the highest frequency approximately six decibels permile. Such a conductor could be .used to reach the first repeater station out'L-of New York, which could be at a distance of-about eight miles, far enough that-the expenseof installing alarge pipe line under the Hudson River and under the densely "populated districts could beavoided. If it appeared more economicalithe B A-inch pipe line. could be terminated at some suburban point, ap- ,paratus provided to reduce the four and a half million cycle band to'thirty-three separate bands each with a maximum frequency of about 140 kilocycles, and a cable containing thirty-three coaxial pairs of quarter-inch diameter run from there to New York. Amulti-conductor cable of suitable type is disclosed in the Dudley application, supra.

In many cases, as where a city off the route of the large conductor transmission line is to be connected into the system, the number of channels required for the branch line would not be sufficient to warrant the installation of a large conductor and its attendant modulating and demodulating equipment. Such a situation might be met by using a multi-conductor cable as just described. Again, it might be preferable to enclose one or more coaxial pairs in a cable containing also a number of voice frequency pairs.

A common situation for which a coaxial conductor transmission system is especially adapted arises from the fact that existing repeater stations are not equally spaced. With systems used heretofore this condition resulted in the attenuation between repeaters being less than or greater than the standard value found to be most satisfactory for the system. The coaxial conductor line, however, can be proportioned so that the desired attenuation will obtain in every repeater section.

Another characteristic of the coaxial conductor transmission line particularly adapts it to use in applicants system. As disclosed in U. S. Patent No. 1,841,473 which issued to E. I. Green on January 19, 1932, the characteristic impedance of extended sections of a coaxial conductor line is determined by the ratio of the diameters of the two conductors. Hence, two lines of different diameters may be joined together directly without occasioning a serious impedance irregularity, (which would result in undesirable reflection phenomena), provided the same ratio of diameters is maintained.

Itis an object of this invention to adapt the conductors of a coaxial conductor transmission line to the irregular spacing of the repeaters therein.

A further and more particular object of the invention is tov obtain an optimum proportioning of the conductors comprising a repeater section in which certain lengths of said conductors are of predetermined diameter.

The inherent immunity of a coaxial conductor circuit from external interference is another consideration that enters into the design of applicants preferred embodiment of his invention. The level of signals transmitted over such a conductor may be permitted to fall to an unusually low value, so low in fact that the molecular disturbances arising in the vacuum tubes and other repeater elements and thermal agitation in the conductor, become the limiting factors in many cases. Because of the concentric disposition of the conductors with respect to each other, the electrostatic and magnetic fields created by signals on the line are closely confined to the annular space between the conductors, and more especially so at the higher frequencies. Both of the foregoing characteristics tend to make crosstalk between adjacent coaxial pairs small.

Other objects and features of applicants invention will appear from a consideration of the following description of a specific embodiment of the invention. In the drawings:

Fig. 1 shows in schematic form the terminal apparatus and circuits employed in an embodiment of applicants invention;

Fig. 2 shows diagrammatically a telephone transmission system embodying applicants invention;

Fig. 3 shows the relative susceptibility of several types of transmission lines to cross-talk; and

Fig. 4 shows in detail an element of the systems of Figs. 1 and 2.

Referring now to Fig. 1, there is shown schematically the general layout of a terminal station. This figure shows the manner in which successive modulation and demodulation are made use of for the purpose of efiecting two-way translation of signals between a common c0- axial conductor line 20 and a multiplicity of ordinary telephone lines 1. The group of apparatus designated 40 includes a plurality of channel modulators 4 for transferring the telephone signals from lines 1 to positions in the intermediate frequency band of modulated waves applied to conductors 42. It also includes a plurality of channel demodulators 5 for reducing the intermediate frequency bands of modulated waves incoming over conductors 43 to their original low frequencies for application to the telephone lines 1. At 50 is shown a group of apparatus for transferring the plurality of bands of singly modulated waves supplied by the several groups 40 to their respective positions in a still higher and broader band of waves applied to line 20. A modulator 44 is therein provided for each of the groups 40. Likewise a plurality of group demodulators 45 are included, each of which effects the preliminary stage of demodulation of a portion of the band of waves arriving over line 20. The output of each of these demodulators is applied to its associated apparatus 40 for further demodulation and eventual application to telephone lines 1.

. The channel modulating and demodulating circuits 40 may be of the types used in ordinary carrier wave transmission practice. For purposes of illustration, three telephone frequency channels are shown in each group; a great many more would be employed in actual practice. Each of the telephone lines 1 is provided with a hybrid coil 2 which separates the outgoing and incoming telephone signal waves; the networks 3 balance the lines. Signals entering the hybrid coil 2 from the subscribers telephone circuit pass through the output windings 38 of the hybrid coil to a modulator 4. The latter is preferably of the type in which the carrier wave is suppressed, as in that described in U. S. Patent 1,343,306, issued June 15, 1920, to J. R. Carson. one side band is suppressed by the respective suoceeding band pass filters 8, 18, 28. The signal bands issuing from these several filters are applied to the collecting bus 38, pass through amplifier 46 and conductors 42 to the second stage or. group modulator in apparatus 50. The frequency of the carrier Waves which are produced by the several high frequency generators 6, 16, 26 and applied to modulators 4, may differ from each other by a little more than the width of the signal band to be transmitted. The separation necessary will depend on the type of filter used. G. A. Campbell Patent 1,227,113, May 22, 191'? discloses a suitable type. The frequency of the In each channel I uppermost band produced by the modulators 4 may be of the order of five hundred thousand cycles per second, that of the lowest fifty thousand. These figures are purely arbitrary, however, and may be varied in accordance with the number of channels to be provided, the number and characteristics of the lines available, and other factors.

The receiving apparatus of each group 40 includes a plurality of band pass filters 9, 19, 29

connected to the distributing bus 39 for separating 1 the carrier wave channels comprising the band of signals applied to thebus from amplifier 47' and conductors43; Following'each of these band pass filters in circuit is a demodulator 5, to which is connected theindividual .high frequency'generators 7, 17, 27. Thedemodulators' and the highfrequency generators may be of the type disclosed in the Carson patent, supra, or of any other suitable types. The frequency of the carrier'wave supplied to each demodulator by its associated high frequency generator is such that final demodulation of theapplied waves is obtained. The resulting audio frequency signals pass to the input windings of hybrid coils 2 and of carrier wave channels are transferred by a sec- 0nd modulation processto positionsin a still wider band of modulated waves and, conversely, a wide band of received modulated waves is separated into a multiplicity of groups each of which is then reduced by-demodulation to'the frequency range of the single modulation carrier system.

As shown in Fig. l, two-way transmission over a single pair of conductors 20 may be used. Differsand to five thousand kilocycles per second and the receiving band pass filter 25 a band of from five hundred to twenty-five hundred kilocycles persecond. Where two or more transmission lines are available between points it is preferred to use separate. lines for each direction of transmission. 1 I

Signalsfrom the channel apparatus-in each group 40 are applied to respective modulators'44. From high frequency "generators 11', 21. 31,} etc.,

carrier waves are supplied, the frequencies of which lie in the range of from three thousand to five thousand kilocy'cles perfsecond and differ from each other by the order of" the group band width. The doubly modulated waves then pass through band filters 13, 23, 33, etc.,.respectivelm,

to collecting bus 10. They are then passed as a band through a common amplifier 48 of suitable design and-the transmitting band pass filter' l5 to transmission line 20. i Y

Signals arriving over the'transmissionlline 20 ,are separated from these outgoing waves by a receiving band passfilter 25. They are then passed throughlamplifier 49 and applie'dto the distributing bus 30. Filters 14,524, 34, etc., di-*' vide'the received band of signals into a number (iii 'willtherefore lie between five, hundred and twenty-five hundred kilocycles per second of groups" of channels. -Eachgroupof waves is then applied to anfindividual demodulator 45, connected to respective sources of carrier waves 12, 22, 32, etc. The frequency of the carrier waves generated are adjusted toreduce the several groups of channels actedon to the range for which the channel circuits 40 are adapted. They specific embodiment described. 1

designed in-accordancewith the principlesun derlying the design of the terminal station illusf trated and described herein. Although chann el" equipment. 40 and group equipment '50 maybe 5 in the system.

numerical in the in close proximity, as at a tenm'nal station, it is' within" the scope or applicants invention to place themiat widely separated points, a carrier wave transmission line of suitable design being used .to connect them. Furthermore, apparatus similar to that of the terminal stations may be connected to the conductor 20 at intermediate points for connection with other points 7 The transmission line 20shown in Fig. 1 comprises an outer cylindrical shell 35, preferably of copper, and an inner one 36', also preferably of .coppenmaihtained in concentric relation therewith by means of insulating spacers 37. The latter are of some'suitable dielectric material of smallloss angle andlow dielectric constant, so that minimum leakage j between the conductors will be. introduced. In some situations, as forexample, .where :it is desiredto connect a-number of groups of first stage modulators to distant second stagemodulators, it may be found advantageousto utilize a multi-conductor cable such as; shown at. 79, in Fig. 4. This cable comprises anumber of coaxial conductors arranged. in a group within a lead sheath 78. "The individual coaxial conductors are designed on the same basis as conductor 20 of Fig. l. The central conductor of each pair may be either tubulanor solid Insulating spacers 77 of porcelain, hard rubber, glass or other suitable material are pro- 'vided at intervals along the central conductor. A

multi-conductor cableof this typeis described in greater detail in the patent application of H; W.1Dudley, supra. Q l l The coaxial conductor type of ylinejas mentioned ,hereinbefore, has certain characteristics which may be taken advantage of in accordance withapplicants invention. The relation between attenuation and frequency of a coaxial conducthe following equation:

tor 'line at high frequencies is given roughly by 115.

where R, G, (land L are the resistance, shunt 120 I conductance, capacity and inductance, respeczerot v y 125,

1 up 11 R sh-( 2) .L=k -logs% V "130 c=-3? 1 where b is the outer diameter of the inner an 135 ductor, c is'the' inner diameter of the outer conduetor, f is the frequency, assumed for purposes of calculation to be the highest frequency of the band to be transmitted, and kn, hi and kz are" constants. The attenuation may therefore be expressed in terms of diameterand frequency as follows: V q

, C v i Dix o to b is preferably maintainedconstant, 1 Y

.two directions, as shown in Fig. 1.

Both L and 0, Equations (3) and (4) respectively indicate, are functions only of the ratio of the diameters of inner and outer conductors. The expression for the characteristic impedance may be reduced to a function only of diameter ratio. A more detailed and precise analysis is contained in U. S. Patent No. 1,841,473, which was granted to E. I. Green on January 19, 1932. As disclosed therein this characteristic enables changes to be made in the diameter of a coaxial line without occasioning reflection phenomena provided the same ratio of inner diameter to outer diameter is maintained.

In Fig. 2 is shown schematically the layout of an extended system suitable for interconnecting distant centers of population and intermediate distribution points. Coaxial conductor pairs of different respective diameters are shown connected in tandem so as to produce an attenuation of the required amount between repeaters and at the same time to accommodate'the physical structure of the conductor to the various kinds of terrain that may be encountered.

At 51 is indicated an urban district at one terminal of the system. The telephone subscribers set 1 is representative of the thousands that may be associated with the telephone central offices of the district. A suburban area is indicated at 52; here a number of ordinary carrier channels from the urban district and a representative one from the surrounding district are shown connected to a second stage modulator for application to a single coaxial conductor line. A tributary line enters at the distant point 54 to join areas 53 and 55 to the system. The first of these areas 53, it may be assumed, does not require a sufficient number of channels to warrant the installation of group modulating equipment; it is therefore connected to the more populous area 55 where the necessary modulating facilities are already available. At a subsequent point on the line a number of high frequency channels are diverted over conductor 93 for transmission to other cities. In the terminal area 56 is located a first stage demodulating apparatus 58. Several channels are subsequently fully demodulated at this point. Other channels may be transmitted as a carrier system to be finally demodulated at 5'7 and eventually connected into an ordinary telephone exchange system 100.

For the sake of simplicity a unidirectional system has been illustrated. It will be obvious, however, that a parallel return system may be provided or that if desired the frequency. range may be divided in order to permit transmission in the In the latter case two-way repeaters, well known in the art, may be used.

Referring now to the details of Fig. 2, there is shown in the urban district 51 a number of first stage modulators 61, preferably of the type shown in Fig. 1, arranged for connection with the telephone system of that district. After signals are here impressed on carrier waves they pass through respective output amplifiers 62 to transmission lines 63 which conduct them to the input amplifiers 64 in the suburban district 52. Sepa-, rate cables may be used for lines 63 or a multiconductor cable such as shown in Fig. 4 may be employed. The telephone exchanges of the area 52 are connected to the first stage modulator 66. The modulated carrier waves from the latter, together with those arriving over lines 63, are ap plied to the second stage modulator 65, which is preferably of the type shown in Fig. 1. The resulting wide band of signal waves is then passed through amplifier; '70 and applied to a pair of coaxial conductors 81.

Between amplifier 70 and the first amplifier or repeater '71 there is indicated a change in the diameter of'the conductors. The first section, 81, is of small diameter. It may be comprised of a small flexible lead covered pair of conductors adapted for installation in the conduits of the local telephone system. At the outskirts of the area, where little difiiculty would be encountered in laying a rigid conductor of large diameter, the section 81 is connected to another pair of coaxial conductors such, for example, as shown at 20 in Fig. 1. While the diameters of the outer conductors may change from a fraction of an inch in section 81 to several inches in section 82, the same ratio of inner diameter of outer conductor to outer diameter of central conductor is preferably maintained. With a given diameter of outer conductor a minimum of attenuation may be obtained when this ratio is approximately 3.6. The optimum figure varies, however, with the maximum frequency transmitted and with the absolute diameters of the conductors, as shown in an application of J. M. West bearing Serial No. 538,647, filed May 20, 1931. Similarly, when approaching repeaters '71 it may be found desirable to use a section 83 of reduced diameter.

The immunity of coaxial conductors from variations in atmospheric conditions and from interference from stray electrical fields may be used to good advantage in accordance with applicants invention. The shunt conductance of open wire lines varies between wide limits as atmospheric conditions change the effectiveness of the insulation between conductors. As a result the apparatus associated with the repeaters-for limiting the input signal level and for controlling the gain of the repeater must be operative over a correspondingly wide range and the full effectiveness of the repeater can be realized only under, optimum conditions. The noise level in an open wire line due to atmospheric disturbances is also considerable, and, more important from the standpoint of operating efiiciency, an otherwise unnecessarily high ratio of signal level to noise level must be maintained. Fig. 3, comparing the cross-talk in open wire circuits, ordinary cable circuits, and coaxial conductor circuits, shows how effectively the coaxial conductor circuit is shielded from interference. Crosstalk in the case of the first two increases steadily with rise of frequency; in the coaxial conductor it decreases and even at fifteen thousand cycles per second is too small to require consideration.

it is of less importance than the noise inherent in the amplifying elements of the repeaters and the resistance noise in "the conductors.

With the lower level to'which signals may be attenuated thus determinedby a relatively fixed noise level instead of by the widely variable one met in open wire sy'stema'it is possible to utilize nearly the full gain of the repeaters' at all times. The conductors themselves can be so proportioned that signals are attenuated between re-" peaters to this limit, the necessity for attenuating pads being in many cases eliminated'andthe requirements of the gain controlling apparatus greatly reduced. I As stated hereinbefore repeaters may be in, stalled in a coaxial conductor line at intervals 7 It wouldbe desirablefor' the sake of uniformity,'and therefore economy,

that each repeater section be identical with every other one in length, diameter, attenuation, etc.,

the apparatus in each being operated at its greatest capacity. Another consideration enters, however, viz., that it is more desirable that the repeaters be located at existing telephone re.

peater oflices within cities and towns, where ex-,

pert attention is available and where the repeater may be associated or combined with local modulators and demodulators and similar apparatus. Between certain points, as '72 andz'l3 of Fig. 2 standard repeater spacing, of perhaps .fifty 1 miles, may be obtained. At another point there may be no telephone repeater station at the fifty mile point and it maybe necessary .that the re.-

peater 72, for example, be only thirty'miles from a the preceding one 71. Again it may be necessary to transmit eighty miles between repeater points, as in section 88 between repeater 74 and repeater 75. This unequal spacing of repeater accordance with the usual practice by inserting attenuating pads, as'at a point justpreceding :the'repeater 72 at the terminal. of the short re peater section ,84, to reduce to', astandard input level the. signals applied to the amplifier. In,

the long repeater section 88 a standard repeater of greater power may be used at '74. In both cases an automatic gaincontrol may be usedin.

conjunction with eachrepeater, with Orwithout the attenuator pad mentioned, to maintain the input to each repeater ata suitable level. The use of attenuating pads, whichihasbeen the practice in the case of open wire lines, is from one view-point a waste of energy, from another it means that the transmission efiiciency of the line is greater than necessary, that a greater line attenuation could be tolerated.

In accordance with applicants preferred ein bodiment of his invention the proportions of concentric conductors are variedto compensate for the dissimilarities in repeater. sections- Equationifi), shows that for a given ratio between theinner diameter of the outer conductor and the outerddiameter of the central conductor the attenuation of a coaxial line, variesfinvers'ely as the size ofthe outer conductor. Given any two points between whichta predetermined attenuation ispermitted, a coaxial conductor of such connect.

Fifty-five decibelswas found to approximate the optimum in one instance. Elimination of attenuating pads is not the only advantage result ing from aproportioning of the conductors to the permissible attenuation between the points they much more significance. This will be appreciated when it is realizedthat the conductor accounts for approximately three-quarters of, the cost of the system,

The economy of conducting material veifectedby reducing the diameters where a higher rate of attenuation can be tolerated'is of It has been seen that the diameter of the conduetors may be changed at will provided'the same diameter ratio is maintained. One section 86 of the conductor between repeater points '73 and 74 for example, may be of limiteddiameter, the following eection87 of large diameter. Even in this circumstance the diameter of conductor. 87 may be so selected that the total allowable "attenuation'between repeaters 73 and '74; is just obtained. Similarly, the conductor 82 need be no larger than is required to make the total attenuation in sections 81, 82 and 83, justequal to the allowable amount. For the thirty mile repeater section 84' mentioned above, the diameter of the; outer conductor might be reduced from perhaps three inches, the sizeused in the standard fifty mile section 85', to three-fifths of this value or approximately two inches. The central'conductor, is reduced'inproportion. Similarly, in the eighty mile section an outer conductor of about five inches diameter instead of the "standard three inch might be used.

While the length of the repeater section is an important factor in determining the diameter of the conductors, the frequency range transmitted is noless so. Attenuation, Equation (6) shows varies approximately with the square root of the 5' frequency; for this reason it isfthe attenuation of the'highest frequency transmitted that is con trolling. Where the uppermost frequency bands are removed from the maimchannel, as by the branch line 93, the following section 88 maybe; designed "with respect to the new uppermost frequency. The relation between the several factors involved as determined fora particular system is shown in tabular form belowl In the first 001-" umn is, represented the inner "diameter of the outer conductor ininches; inthe second, the number of miles between repeaters; inthe third, the maximum frequency to lrpe transmitted, in kilocycles per second; and in'the fourth, the number of one-way channelsprovided.

Diameter of r N umber Repeater Maximum qgfiggi spacing frequency 25 3 3 3 in. 100 mi. 1100 kc/s 250, 3in. 50mi. :4500kc/s 900 2 in. v 100 mi. 450 kc/s 2 in. 50 mi. 1700 kc/s 340- 2 in. 25 mi. 7300 kc/S 1450 l in. 50 mi. 500 kc/s i :1 in. 25 mi. 2000kc/s A in. i 25 mi. -.500 kc/s 120 4in. 25 mi. 140 kc/s so Immediately following repeater" 73in circuit there is shown a tributary transmission line 108. The latter "introduces signalsfrom the second stage modulator 105, which in turn is fed by a local first stage modulator 103 and a similar 'modnals transmitted by amplifier 73 or a band which has been, left vacant for them, or which has previously been diverted. Band pass filter 106 is designed to pass only these channels. From the main line there branches off, just before the next repeater station 74 is reached, a line 93. The band pass filter 91 prevents all except the selected channels from entering this branch. At 94 in the branch line is represented a short section of small diameter such as might beused at a river crossing or under the streets of a town in the path of the transmission line.

Returning now to the main line, there is shown at the terminal of thelong section 88 an amplifier '75 and a first stage demodulator 58. Several groups of channels may immediately thereafter be fully demodulated in apparatus 59 and the resulting telephone frequency channels connected into the local exchange system. Another group may be transmitted at carrier frequencies over line 60 to the distantly located demodulator 57, for eventual connection with the telephone exchange 100.

The particular values of dimensions and frequencies set forth herein are only for the purposes of illustration. The principles underlying the proportioning of the conductors may be applied to coaxial conductor systems generally with little restriction as to the diameters, frequency, repeater spacing and the particular type of line used, whether it be a single coaxial pair, a multiconductor cable or equivalents thereof, within the scope of the appended claims.

What is claimed is:

1. In a signaling system, a transmission line comprising a central conducting path and an outer cylindrical return conducting path. coaxial therewith and insulated therefrom, amplifiers at irregular intervals in said line, the attenuation between successive amplifiers being the same and comprised substantially only of the attenuation of said transmission line.

2. Ina communication system, a transmission line divided into a plurality of sections having different rates of attenuation, eachof said sections, comprising a central conducting path and a cylindrical return conducting path coaxial therewith, and amplifiers at a plurality of points in said line, thelength of said sections and the rates of attenuation therein being such that the line attenuation between successive amplifier points at the maximum frequency to be transmitted therebetween is the same throughout said line. i

3. In a communication system adapted to trans- "mit a wide band of frequencies, a line comprised of a central conductor and an outer cylindrical conductor coaxial therewith and insulated therefrom, and a plurality of repeaters in 'said line, said line being divided into a plurality of sections having different diameters of conductors, the diameters of said conductors in said sections being such that for the maximum signaling frequency the total attenuation between each of said repeaters is the same and comprised substantially only of the attenuation of said line.

4. In a system for the, communication of intelligence, a transmission line, a plurality of repeaters at unequal intervals therein, said line comprising an inner conductor and an outer cylindrical return conductor coaxial therewith and insulated therefrom, the rate of attenuation of the signals of highest frequency transmitted between said repeaters varying inversely with the distance between said repeaters.

"5. A system in accordance with claim 4 in which the diameters of said conductors between said repeaters are directly proportional to the distances between said repeaters and the square root of the maximum frequency to be transmitted.

6. In a system adapted to transmit signaling waves of a wide. range of frequencies extending to at least one hundred thousand cycles per second, a transmission line comprising a pair 0f conductors spaced in coaxial relation to each other and separated by an insulating dielectric, and a plurality of repeaters at irregular intervals in said line, the diameters of conductors between successive repeaters being so proportioned with respect to the maximum frequency to be transmitted and to the distance between said repeaters that said signaling waves are reduced to a level determined chiefly by the noise level in said system.

7, A combination as defined in claim 6 in which said reduction of signal level is caused substantially by the attenuation of said conductors alone.

8. In a communication system, a transmission line comprising a central conducting path and an outer tubular return conducting path concentric therewith and separated therefrom by a dielectric which is chiefly gaseous, a plurality of amplifiers at predetermined irregular intervals in said line, said outer path having between said successive ones of said amplifiers sections of unequal diameters, the diameters and lengths of said sections being so mutually proportioned that signals are reduced between successive amplifiers by the attenuation of said conductors alone to a level determined chiefly by the level of molecular noise.

9. In a communication system, a transmission line comprising a central conducting path and an outer tubular return conducting path concentric therewith and separated therefrom by a dielectric which is chiefly gaseous, a plurality of amplifiers at intervals therein, the diameter of said outer path varying in sections between certain of said amplifiers; the lengths and diameters of said sections being so related to each other that signals are attenuated in the same degree between successive ones of said amplifiers substantially by the attenuation of said transmission line alone. 7

10. In a communication system, a transmission line, a plurality of amplifiers at irregular intervals therein, said amplifiers being operative over a restricted range of input signal amplitudes, the attenuation constant of said line being different in different sections between said amplifiers and so proportioned to the lengths of said sections and the output levels of said amplifiers that between said amplifiers, signals are reduced substantially by the attenuation of said line alone to a level within said operative range of said amplifiers. V

11. A communication system having therein a transmission line comprising a plurality of sections of concentric conductor cable adapted to transmit with small attenuation frequencies of at least one hundred thousand cycles per second, a plurality of repeaters at intervals in said line, the attenuation constants of said sections being unequal and so proportioned with respcct to each other and the lengths of said sections between successive repeaters thatsubstantially the total signal attenuation between said repeaters occurs in said line and is the same throughout said system.

12. A carrier wave transmission system 'comprising in combination at a terminal thereof, a

plurality of telephone exchanges, a central station, means at each of said exchanges for translating speech frequency signals to and from respective positions in a band of carrier frequencies, means comprising transmission lines individual to said exchanges for conducting signals in said carrier'frequencyband between said respective exchanges and said central station, means at said central station for translating said carrier frequency bands to and from respective positions in a wider band of carrier frequencies, and a transmission line for conducting said wider band of carrier frequencies between said central station and remote terminals.

13. A carrier wave transmission system comprising in combination at a terminal thereof, a

plurality of telephone exchanges, a-central station, a coaxial conductor transmission line connecting each of said exchanges with said central station, 'means at each of said exchanges for translating signals ina multiplicity of speech frequency channels to respective positions in a wide band of carrier frequencies, means to apply said signals to said respective transmission lines, means at said central station for translating said bands of carrier frequency signals to respective positions in a band of frequencies of the order of megacycles in width, a coaxial conductor transmission line for conveying said last mentioned band of signals to remote distributing points, and means at said terminal of said system for correspondingly, inversely operating on signals received over said last mentioned transmission line. i

14. In a carrier wave transmission system, a

plurality, of groups of signal wave channels, a

7 transmission line associated with each of said groups, means to impress the signal waves of each of said'groups on carrier waves of different frequencies for transmission over said lines, an-

other transmission line, means in each of said.

first mentioned lines to impress the waves therein on a carrier wave of higher frequency for transmission over said last mentioned line, demodulating means to receive the doubly modulated signal waves from said last mentioned line, means at an intermediate point of said second mentioned transmission line to divert a band of waves transmitted thereover, and demodulatingmeans to restore the signal waves impressed on said band of diverted waves to their original frequencies.

'15. In a carrier wave transmission system, a plurality of groups of signal wave channels, a. transmission line associated with each of said groups, means to impress the signal waves of each of said groups oncarrier waves of different frequencies for transmission over said lines, another transmission line, means in each of said first mentioned lines to impress the waves therein on a carrier wave of higher frequency for transmission over said last mentioned line, demodulating means to receive the doubly modulated sig-' nal waves from said last mentioned line, means at an intermediate point on said second mentioned transmission line to select a band of waves transmitted thereover, a second transmission line, means to partially demodulate said band of waves and to apply them to said second line, and means to demodulate finally the waves transmitted by said second line.

MAURICE E. STRIEBYL

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