US1624646A - Transmission system - Google Patents

Description

Apr11 12, 1927. W. V. WOLFE TRANSMISSION SYSTEM 1925 2 Sheets-Sheet l Filed July 51,

T /m/eH/o/f.- l/Vd//ace V. WO/f.

April 1 2 ,n 11927.

, D /30 /l/F-e N l W. V. WOLFE TRANSMISSION SYSTEM Filed July 31, 1923 I 2 Sheets-Sheet 2 f/g. 5

/Vf-f /n Ven/0r: y Vl/a//dce M WO/f Patented Apr. 12, 1927'.

WALLACE v. WOLFE, OF CORONA,

PANY, INCORPORATED, 0F

NEW YORK,

NEW YORK, ASSIGNOR `TO WESTERN ELECTRIC COM- -N. Y., A CORPORATION 0F NEW YORK.

TRANSMISSION SYSTEM.

Application led July 31,

This invention relates to a transmission system having electric wave filters such as are employed'in multiplex carrier waveqslgnaling systems.

Typical carrier wave signaling systems are Vdescribed in an article by Messrs. Colpitts 4and Blackwell entitled Carrier current telephony and telegraphy which was published in the Transactions of the American Institute of Electrical Engineers, Volume XL, 1921. In the arrangement illustrated in Figs. 42 and 49 of that article, the several transmitting band filters in a given system have their end sections all connected in series with each other and the common transmission circuit. Likewise, the several receiver band filters have their end sections connected in series with each other and with the common receiving circuit. The common transmitting and common receiving circuits are then conjugately connected to a common transmission line by means of ahybrid coil and balancing net-work. In other carrier wave signaling systems not described in that article, all of the band filters, both transmitting and receiving have their end sections connected in series with each other and with the common transmission line. In still other systems the band filters have their end sections connected in parallel.

1n the carrier Wave signaling systems employing band filters which were first developed, non-magnetic material, such as wood,

was used for the cores of the inductance coils in the filters. In order to obtain the necessary inductance in such coils, they were necessarily large and expensive. In. later systems, both the size and expense were reduced y using magnetic material for the cores of the inductance coils in the filters. In these later systems, however, trouble was experienced due to cross-talk and interference between the several channels An object of the present invention is to improve the operating characteristics of such systems without materially increasing their cost and space requirements.

According to the presentimiention, multi-section filters of the general type described in G. A. Campbell Patent No. 1,227,113, May 22, 1917, are made up with two kinds of inductance coils one having a core of non-magnetic material and the other of magnetic material, Such filters are used in multiplex 1923. Serial No. 654,808.

carrier wave signaling systems and the end sections of the filters which are connected either in series with each other and with l' the common transmission circuit or in parallel with each other with respect to the common transmission circuit comprise inductance coils having cores of non-magnetic material. The remaining inductance coils in each filter have magnetic cores. Such an arrangement substantially prevents cross-talk and interference between the several channels which cross-talk and interference applicant discovered was due to magnetic modulation in the inductance coils of the end sections of 'the filters.

The novel features, which are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof will best be understood by reference tothe following description taken in connection with the accompanying drawings illustrating the invention in which Fig. 1 shows diagrammatically a multiplex carrier wave signaling system, in which the end sections of the filters are connected in series. Figs. 2, 3 and 4 show modified arrangements for connecting the several transmitting and receiving circuits to the common transmission medium or line. Fig. 5 illustrates one Way of connecting the end sections in par- `allel to the common transmission circuit.

Referring now to Fig. l a plurality of two-way carrier wave signaling channels I, II and III are shown connecting signaling stations A, B and C, respectively, to a common transmission line ML The signaling stations'A, B and C may scribers telephone stations or ordinary telephone exchanges. They are connected to the two-Way carrier Wave signaling channels by means of low frequency circuits L, L2 and L3, respectively.

Transmissions in the several .two-way channels I. II. and III are effected by carrier waves of different frequencies. Corresponding elements inv the several channels, however, are much alike, differing only to the extent necessary to accommodate the differ-v ent frequency carrier waves employed. Thereforer'a detailed description only of the elements of channel I will be given.

be ordinary sub- Corresponding elements in the several channels are designated by the saine reference letter, the channel being designated by the numeral following the letter.

The two-way carrier wave channel I has in its transmitting branch an oscillator O1, a modulator M1, and a band lilterMF1. The receiving branch of carrier wave signaling channel I includes a detector band filter DF1, a detector and amplifier DA1 and a voice frequency filter F1. The low frequency circuit L1 is conjugately connected to the transmitting and receiving branches of channel I by means of a hybrid coil H1 and balancing network N1.

Oscillator O1, modulator M1, and detector and amplifier DA1, may'be of any suitable design but are preferably of the vacuum 'tube type. Devices suitable for this purpose are described in the Colpitts and Blackwell article supra. The modulator band filter MF1, and the detector band filter, DF1, comprise series and shunt impedance elements and are preferably of the genera-l type disclosed in the Campbell patent hereinbefore mentioned. These wave filters have precomputed values of inductance and capacity of such values that the structure transmits with practically negligible attenuation sinusoidal currents of all frequencies lying between two selected limiting frei quencies while attenuating and approximately extinguishing currents of neighbor-V lng frequencies lying outside of'said limiting frequencies.

1Wave filter MF1 comprises a plurality of series condenser-s 15 and a plurality of shunt sections such as 8, 22, 23 and 24, each comprising an inductance coil and a condenser. The inductance coils 16 and 17 of shunt sections 8 and 22 have cores of non-magnetic material, such as wood, while the inductance coils 18 and 19 of shunt sectionsv23 and 24 have cores of magnetic material. The shunt section 8 includes a condenser 20, and shunt sections 22 and 23 include condensers 21. The shunt section 24, which is electrically nearest to the transmitting oscillator O1, includes a pair of condensers 25 in a branch which is grounded at its mid-point.

`Wave filter DFI is similar to wave filter MF1, except for the values of the constants of the inductive and capacitive elements, which depend upon the frequency of the `current to be transmitted.

In one system to which the invention has been applied, all of the currents used for transmission at a given station have frequencies lying within one frequency range, while the currents used for reception have frequencies lying in a separate range. Such a system is -known as a grouped frequency carrier wave signaling system.

The end sections 8 to 13 inclusive of the Several transmitting and receiving band filters arc connected in series with each other and a common transmitting circuit 14, which in turn is inductively coupled to a common transmission mediumor line ML.

It is obvious that, since the end sections 8 to 13 inclusive are all connected in series with each other, current ofall the frequencies used for both transmission and reception will be present toa greater or less extent in the inductance coils of these end secions. If the cores of these inductance coils are composed. of magnetic material, intermodulation takes place between the currents of these several frequencies and components of current may be developed which cause interference between the several channels. It has been found that these interfering components are developed primarily in the end sections of the filters and to alesser eX- tent in the adjacent shunt sections. Accordf ing to the present invention, the inductance coils of these end sections have cores of nonmagnetic material and, therefore, the production of such interfering components of current is obviated.

In one of the systems hereinbefore mentioned, to which this invention has been applied, carrier waves having frequencies of 6, 9 and 12 kilocycles are used for transmission in one direction and carrierwaves having frequencies of 15, 18 and 21 kilocycles, in the opposite direction. Currents having a range of frequencies of approximately 2 kilocycles have been found satisfactory for ordinary telephone conversations. In the particular system under discussion the carrier currents and the corresponding lower side band currents of the lower group of frequencies are transmitted in one direction While the carrier currentsand the corresponding upper side band currents of the higher group of frequencies lare transmitted in the opposite direction. Consequently currents havin@ frequencies of 4 to 6, 7 to 9, and 10 to 12 kilocyc'les are transmitted for example from the terminal station of Fig. 1` and currents having frequencies of 15 to 17, 18 to 20, and 21 to23 kilocycles are received thereat. i,

A representative allocation of. these frequencies t0 the several transmitting and rcceiving branches is shown in the following tabulation Range of Filter Carrier Mld-fresque-naaste characters kllocy cles kilcydes kllocyc-les MF1 6 4 to 6 5 MF2 9 7 to 9 8 MF3 12 10 te 12 11 DF1 15 15 t0 17 16 DFz 18 18 to 20 19 DFl 21 21 to 23 22 From a perusal .of the frequencies involved in the tabulation above, 1t will be iso seen how interfering currents can be developed due to intermodulation.

It is a well-establishedfact that coils con` taining cores of magnetic material will so distort a pure sine wave that the output o the coil will have as itscoinponents the odd harmonics of the applied frequency.

This may be stated thus:

(l) A sine 2H ftzA sine 2H ft}- B sine3 2H ft-i-C sine5 2H ft etc.

where f: frequency t=time In carrier wave telephone systems where a number of sine wavecurrents are impressed upon, or passed through the same coll, 1fy

the core of the coil contains magnetic material the output wave will contain frequencies not present in the input Wave and frequencies that in carrier telephone systems will cause cross-talk. v

Let, (1 M sine 2II ft (the carrier frequency) QIN vsine 2H ft (the side band frequency); VIP sine, 2H ft (the voice frequency) ;-and also C-l-VZQ, and M, N and P are constants designating the respective amplitudes of the waves. Then substituting in equation (1) the carrier waves C1, C2 and C3 and the side band frequencies Q1, Q2 and Q3 present in the output of a carrier wave system, we have (2) Cl-I-CQ-l-Cg -i-Ql-l-Qz-i-Qs u 1 z i-Cs )|f1(C13+C23l-C33 Q13+Q23+Q33 )+3k1(C12Q1-i Q C 2 C 2Q2 2 3...)5 ..etc.

When the individual terms in equation (2) are analyzed it will be seen that they contain frequencies that will produce cross-talk. For instance C12Q2 is equivalent to a frequency of twice Gli-Q2 and CICZQ3 is a frequency equivalent to the algebraic sum of C,iC2iQ3.

The fifth power term which has not b'een expanded contains, however, some very interesting terms. The term CIQCJQ3 is a frequency equivalent to twice one carrier :L-

'twice any other carrier i any side band, and

itis this term which has given considerable trouble as it produces right side up cross-v talk:

Most of' the terms in thecube-term resultin non-intelligible cross-talk, sometimes completely inverted speech and at'other times fthe second harmonic of the speech frequencies. F or an example of cross-talk produced by the cube-term, let us assume that the carrier frequencies are 6, 9, 12, 15, 18 and 21 kilocycles as given in the tabulation above. The term C12Q2 will be equivalent to .twice kilocycles i the side band of the 9 kilocycles channel, which, .making the assumption of a 1500 cycle input frequency would 7.5 kilocycles. The sum of these terms would be 19.5 kilocyclesand would produce cross-talk in the 18 kilocycle channel of 1500- cycles. v

In this particular example as the voice frequencyis increased the side band frequency on the l9 kilocycle channel is deadapted to cooperate with the terminal sta' tion of Fig. 1. For each transmitting branch of the station of Fig. 1 there is a cooperatingreceiving branch at the distant station and for each receiving branch of the station of Fig. 1 there is a cooperating transmitting branch at the distant station.

While' only three channels have been shown in Fig. 1, additional channels may be added as indicated by the dotted extension of the common transmitting circuit 14. In similar manner additional channels may be added in the other figures.

In Figs. 2, 3 and 4, the transmitting and receiving filters Yare indicated by blocks but it is to be understood that they are identical with the filters bearing the same reference characters in Fig. 1.

Inythe arrangement of Fig. 2, all of the transmitting band filters are connected together as a group, while the receiving band lilters are connected together to compose a, separate group. The transmitting group is electrically coupled to the transmission line 4ML by means of a shieldedl transformer 30,

while the receiving group is connected to thesame line-by means of the. shielded transformer 31. In this modification, the-transmitting filters as a group are not conductively connected to the receiving filters as a group, but all of the transmitting and receiving filters are nevertheless electrically connected in series.

In the modification of Fig. 3, the trans,-

mitting filters and the 'receiving filters are grouped as in Fig. 2. In this arrangement, however. the separate groups are ,conjugately connected to a transmission line ML by means of a hybrid coil 32 and carrier wave balancing network MN. I

In the modification of Fig. 4, all of the. filters have their end sections'connected in vnetic material.

series with each other but the arrangement is such that the transmitting filters are adjacent to each other and likewise the receiving filters.

In the arrangement of Fig. 5 the several transmitting and receiving band filters are connected in parallel with respect to the common circuit 14, which in turn is connected to the common line ML. In this arrangement the band filters are preferably terminated in a mid-series section, instead of in a mid-shunt section as shown in the other modifications. lThe mid-sries termination is illustrated in Fim 5.

W'hile the detailed description of the invention has been. limited to specific arrangements of the filters, other arrangements will be obvious to those skilled in the art andthe invention is to be limited only by the scope 2. In combination, a transmission line, a source of carrier waves associated therewith, and a Wave filter comprising a plurality of inductance coils one of which is connected to said line, the coil connected t0 said line having a core of non-magnetic material and others of the coils having cores of magnetic material.

3. 'In combination, a transmission line, a source of carrier waves associated therewith, and a Wave filter comprising a pluralityofvshunt inductance elements one of which is connected to said line, the shunt inductance element which is connected to said line consisting of non-magnetic material and others of said shunt inductances elements lconsisting in part at least of magnetic material.

4. In combination, a transmission line, a source of carrier waves, and a wave filter comprising a plurality of inductance coils connected between said line and said source,

a coil near the end of said filter adjacent the transmission line having a core of non-magnetic material and others of the coils having cores of magnetic material.

5. In combination, a transmission line, a source of carrier waves, and a wave filter connected between said line and said source and comprising a plurality of sections each having a shunt inductance element, the shunt inductance element near the end of said filter adjacent the transmission line consistsystem, a transmission medium,

ing of non-magnetic material and others of said shunt inductance elements consisting in part at least of magnetic material.

6. In combination, a circuit over which a plurality of Wave components of different frequencies are transmitted, a second circuit in which it is desired that only certain of said components flow, and a band filter selective of the desired Wave components connecting said circuits and including a plurality of shunt inductance elements, the shunt inductance element nearest said first mentioned circuit consisting of non-magnetic material and others of said shunt inductance elements consisting in part at least of mag'- netic material.

7. In a carrier wave signaling system, a transmission line over which a pluralityvof different frequency groups of carrier waves are transmitted, a circuit traversed by only one of said frequency groups of waves and a band filter connecting said transmission line and said circuit and including a plurality of series elements and shuntinductance coils having precomputed values depending upon the upper limiting frequency and the lower limiting frequency of the group to be transmitted to said circuit, the shunt inductance coil adjacent said transmission line having a core of lnon-magnetic material and others of said coils having cores of magnetic material.

8. In a multiplex carrier Wave signaling a plurality of carrier Wave channels, an electric Wave filter connected in each channel consisting of a plurality of sections, each section havlng a shunt inductance element, means to connect one shunt lnductance element of each filter in series with each o'her and with the common transmission medium, said serially connected shunt inductance elements consisting of non-magnetic material and others of said shunt inductance elements of each filter consisting in part at least of magnetic material.

9. In amultiplex signaling system, a terminal station, a transmission line, a plurality of transmitting branches at said terminal station. a plurality of receiving branches also at said terminal station, a band filter in each of said branches, each of said filters having a plurality of shunt impedance elements, means to connect one shunt impedance element of each of said filters in series with each other and with the transmission line, said serially connected shunt impedance elements consisting of coils having non-magnetic cores, another shunt impedance element of each filter consisting of a coil having a core of magnetic material.

10. In a carrier Wave signaling system, a terminal station, a transmission'line, a transmitting branch and a receiving branch at lil?.

said station, a ilter in each of said branches, l

each of said filters having a plurality of shunt impedance elements,l means to connect one end shunt impedance element of each of'said filters in series with each other, and means to associate the terminal station with the transmission line, said serially connected shunt impedance elements consistingv of inductance coils having cores of 'nonmagnetic materlal and ,others f said shunt A impedance elements of each filter consisting of -coils having cores of magnetic material.

11. In a multiplex signaling system, a. terminal station, a transmission line, a plurality of transmitting branches at said terminal station, a plurality of receiving branches also at said terminal station, a band filter in each of said branches, each of said'ilters having aplurality of shunt impedance elements, means to connect one end shunt impedance element of each of said filters in series with each other and with the transmission line, said serially connected shunt impedance elements consisting of coils having non-magnetic cores, another shunt impedance element of each iilter consisting of a coil having a core of magnetic material.

12. In a multiplex carrier Wave signaling system, a transmission medium, a plurality lof carrier wave channels, an electric wave filter connected in each channel consisting of a plurality of sections, each section having a shunt inductance element, means to' connect the shunt inductance elements of one end section of each filter in such electrical relationship with each other that each is affected by the electrical conditions of the others, said connected shunt inductance elements consisting of Inon-magnetic material and others of said shunt inductance elements of 'each filter consisting in part at least of magnetic material. j

In Witness whereof, I hereunto subscribe my name this 28th day of July,'A. D. 1923.

WALLACE v. WoLFE.

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