US1714697A - Electric-wave transmission system - Google Patents

Description

May 28, 1929. G. H. sTx-:vENsoN :1,714,697

ELECTRIC WAVE TRANSMISSION SYSTEM Filed May 2, 1925 Patented May 28,1929.

GEORGE H. STEVENSON, OF NEW YORK.

vApplication led May 2,

This invention relates to. electric wave transmission systems and more particularly to means for generating and selectively transmitting electric waves.

An object of the invention is to generate electric waves and to selectively transmit the generated waves to a load device.

Another object is to selectively transmit complex waves and to prevent the production of transient surges in the transmission `path.

An additional object is to compensate for reactance in a path traversed by electric waves to render it substantially non-reactive.A

A further object is to neutralize the ,reactancefof a band transmission network by another reactive network to produce a nonreactive network ot' constant impedance for all frequencies both within and without the transmission band. f

An additional objectis to prevent current or voltage surges lof large amplitudewhen an electric current traversing reactive paths is varied. c

A featulc of the invention is a network s included in an interrupter circuit which has a constant non-reactive impedance for all frequencies and a broad band filter transmission characteristic.

-Another feature is an interrupter having' its magnet winding included as an element of a non-reactive network. f A VJfurther feature is a means for coupling space discharge tubes, which means comprises a broad band filter having jparallel paths, one bearing a complementaryrelation to: the other, whereby the two form a' nonreactive, const-ant impedance" path at all frequencieseither within or without the transmission band.

lVhen an electric currentis interrupted or the impedance of the path which it' traverses is subjected to adrupt changes, waves or surges of current or voltage or both, of large am litude may be produced if the path inclu es reactive element-s. A practical illustration of a case where such surges are likely to occur and where they are detrimental is in a circuit for generating yvarying current by means of a circuit interrupter such as has `been employed in telephone systems for generating low lfrequency currents for ringing purposes.

e It is now known that waves of rectangular YORK, N. Y., ASSIGNOR, TO WESTERN ELECTRIC COMPANY, INCORPORATED,

I Technical Journal A CORPORATION OF NEW ELECTRIC-WAVE TRANSMISSION SYSTEM.

1925. serial No. 27,376.

form, such as are produced by interrupting a direct current, contain an infinite series of components with difierent amplitudes. See an article by Ralph V. L. Hart-ley entitled ARelations of carrier and sidebands in radio transmission published in the Bell System for April, 1923, page 90. Then waves of this form are generated in or transmitted over a circuit including reactive paths, the resonance property of the reactive elements causes the components of the wave corresponding to the resonant frequencies to develop currents or voltages of large amplitude which may be termed surges or transients For example the winding of the interrupter magnet in a ringing interrupter system of this kind will ordinarily provide a resonant path, since it has inductance and distributed capacity and hence will cause transient surges of detrimental character, One disadvantage resulting ence of these surges in a telephone line, for example, is that inductive interference between adjacent lines may be produced. Another disadvantage is that the surges may be of a frequency such as to cause undesired operation of Abells or otherkg signals in the system. y

If a filter network of the ordinary kindI be provided to` discriminateb'etween desired and undesired frequencies, the reactances of the filter elements will likewise provide resonant paths for producing other transients in the manner explained above.

In the present invention, a broad band filter network is included in a circuit with a variable impedance device and a source of current, representative of any source of complex waves, and a load circuit., representing any desired form of wave receiving arrangement or device. The filter network, as a whole, comprises two parallel paths or complementary filters so designed that their resultant impedance measured at the input terminals is a constant resistance frequencies. Each filter has a broad band transmission characteristic and the two combined have a similar characteristic.

The two paths of the iilter are rendered complementary by providing series impedances in one corresponding to shunt admittancesin the other, series coils corresponding to shunt condensers, series condens- BY MEsNE ASSIGNMENTS,

from the pres-- at all y components of its impedance should be very large as compared to its reactive component. This requirement is ordinarily met in etlicient signal receiving arrangements.

The invention is illustrated in the drawings wherein:

Fig. 1 represents an interrupter circuit including a filter having a non-reactive impedance;

Fig. 1a represents a modified terminal element for the filter of Fig. 1; and

Fig. 2 represents a wave translating circuit including space discharge tubes coupled by means of a non-reactive band pass filter.

In the several iguies of the drawings like reference characters have been used to indicate like parts.

The circuit shown in Fig. 1 comprises a variable impedance device, namely an interrupter 10, including a magnet 11 having an armature 12 and a Contact 13. The winding ot magnet 11 is included in a circuit with a battery 14 in series withcontact 13 and armature 12. The winding of magnet 11 is shunted by a path including a resistance 15 in series with a capacity 16. The terminals 17 and 18 of the interrupter connect to the input terminals of av band filter 19 including terminal impedance elements 20 and 21 preferably resistances.

The band filter 19 includes parallel transmission paths or component broad band filters 22 and 23. Path 22 has series inductancc elements 24, shunt inductaiice elements 25, series capacity elements 26 and shunt.ca,`

pacity elements 27. Path 23 contains similar elements 24', 25', 26 and 27 The two paths of filter 19 have their output terminals connected to. independent .primary windings of a three-winding transformer 28, the secondary winding of'which is connected to a resistance in path 30 representing any eiicient load circuit or device the impedance of which is chiefly resistance.

The transformer 28 may be omitted and resistance 30 replaced by the elements shown in Fig. 1a which include separate resistances 31 and 32 representing separate load devices or elements arranged to be connected to the respective output terminals of the vpaths 22 and 23. i l

The winding of magnet 11 is energized by means of current from battery 14 whereby its armature is caused to alternately/open and close contact 13. Interrupter 10- and battery 14 represent any desired source of lcomplex waves. The current supplied from source 14 to filter 19 is thus substantially in the form of rectangular waves. It has been explained that when a direct current is interrupted or when Waves of rectangular form are supplied to a path including reac tance elements that surges or transient voltages or currents will ordinarily be produced. In the present invention, however, the path Vincluding the elements 15 and 16 is provided to compensate for the reactance of the winding of magnet 11 to render the wholey path non-reactive. Tn order for the one path to compensate for the other their respective time constants niust be the same and their resistances must be equal. Again, the paths 22 and'23 of filter 19 are designed to be of a complementary nature, so far as the reactance of these paths is concerned, so that the i filter, as a whole,visjsubstantially non-reactive at all frequencies. By virtue of this fact, when waves of rectangular or other complex form or interrupted direct current are supplied to the filter 19, transient surges are prevented from being produced in the input circuit. Moreover, the',J filter functions 'to transmit a desired band of fre-y quencies from the intei'rupter 10 to the loadA and to exclude any undesired frequencies which may be present as components of the rectangular waves produced by the source. 'In addition, the impedance of filter 19 is constant for all frequencies.

The resistances 30, 31and 32 may be replaced by any load circuit or device, such, for example, as a telephone line including telephone ringers and the like.

In order that path 22 of filter 19 may be the proper counterpart of path 23, the series coils 24 in one correspond to shunt condensers 27 in'tlie other and the Series condenseis 26 in one path correspond to bridged or shunt coils 25 in the other path. Y

In the article entitled Theory and design of uniform and composite electric wave filters by Otto J. Zobel, published in The Bell System Technical Journal Vol. II,

January, 1923, page 1, it is shown that, 4to

any non-dissipative reactance network there corresponds an inverse reactance net-.

Work which is so related that the product 'of their impedance is a constant, independent vof frequency. The rules byv which vin'verse networks may be designed are developed under the heading Theorem i2-jon page 360i theabove journal.

It may further be shown Work of filters 19 of Figf 1 and 19 of Fig. 2,

the product of the corresponding imp edances of the component-networks vis a constant and moreover that the result-ant impedance. isv a pure resistance. A

-Let Zrepresentthe'impedance of either `filter or 19 measured at theI input ter- RZ1 RZ2 R+Z1+1ie+z2 R when 'Z,Z2=R2. This expression sets forth the relation which impedances Z, and Z2 must bear to each other in order that the total impedance Z shall be a constant resistance; in other words,in order that the filters 19 or 19', as thecase may be, shall be of non-reactive and constant impedance. If one impedance Zl be given, the impedance Z2 may bedetermined from these relationships as set fort-h by Zobelin the above mentioned article.

f nowin a practical case one branch of the filter 19, such as branch 22, be designed that filter to be a broad band filter of a particular type, then in accordance withy the present invention an inverse network 23 may be designed and this inverse network will be a broad band filter having transmission characteristics similar to the network 22. l

In the present instance filters 19 and 19 comprise each a filter 22 of the constant k type. The distinguishing characteristic of a constant k filter is that the product of its series and shunt impedances is a constant real'quantity dimensionally of the type (resistance) 2. The inverse filter network 23 in each case is also a constant c filter. It is not to be understood, however, that these filters are necessarily of this type for they may be of any general type whether constant A 1 or not, this particular-type of filter having been used as an illustration merely from conlsiderations of convenience.

In order that 'the construction of an inverse filter network may be better understood, a practical case will now be illusstrated. For this purpose, in Fig..2 the various shunt and series elements of the component filters are designated as Zm Z 217 Z12 and Z22, respectively. It is to be noted 22 is terminated in mid-series at 4both ends, whereas flter23 is terminated in mid-shunt at both ends.

Ifit be assumed that the filter 22 is the given impedance Z1, then applying the rules laid ddwn by Zobe the reciprocal network 23 may bev constructed, in whichY series ele-v y ments correspond to 'shuntplements of the filter 22 and vice versa, and series .combinations of elements 1n one correspond to shunt combinations of elements in the other. The

vrelationships which must exist between various impedances are as follows:

I R1R2=Z11Z22-=Z21Z12=-R2 This equation shows that the propagation constants-of the component filters are alike,

since by well-known filter theory Cosh P1=1+}% 2l Cosh P2=1 +lg`12 22 where P1 and P2 are the respective propagation constants of a single complete section of each filter respectively. A

In Fig. 2, a filter 19 in general similar to the filter 19 shown inF ig. 1, is arranged to couple the output circuit of a space discharge repeater 35 to the input circuit of a second space discharge repeater 36. Repeaterl 35 includes aspace discharge tube 37 having a grid cathode and anode. Input terminals 38 and 39 are connected to the grid and cathode respectively and are shunted by a resistance 40 which provides a leak path for currents between thegrid and cathode.

` A battery 41 of suitable electromotive force is provided to supply tube 37. The output circuit of tube 37, which is connected to its anode and cathode, includes 'a source of space current represented by battery 42 connected in series with a choke coil 43.' The output circuit is coupled to the filter 19 bymeans of a condenser` 44. The outputterminals of transformer 28 are connected to the input electrodes of a space dischargev` tube 45 and include in shunt thereto, the

resistance 30. In series in the input circuit of space discharge tube 45 is included a battery 46 for supplying a suitable 4average potential to the control electrode. The output circuit of this tube also includesa space current source 47 in series with choke coil 48 and is connected to output y and shunted by a high impedance repre= sented by resistance 49. Electric waves of any desired form may be supplied-to the input circuit of tube 37 to produce fluctuations of the potential upon` the control electrode thereof and to cause corresponding .fluctuations in the current traversing the space path in the tube. Byproviding batteries 41 and 42 having suitab'le voltages, the fluctuations produced inthe output circuitof tube 37 may be caused'to be of greater am'- plitude than theco'rresponding Waves su plied to its inputJ circuit. Filterr19 serves llO terminals 29 to selectively transmit 'the waves suppliedA which may supply any suitable load circuit,

or device, as already mentioned in connection with Fig. 1. Filter 19 may be designed to passany desired band of frequencies and to exclude frequencies outsidev of the selected band. Moreover, this filter which includes the two paths-22 and 23, similar to corresponding paths of filter 19, is preferably rendered non-reactive by making one path thereof the counterpartof the other. That is, series coils in one correspond to bridged condenser-s in the other, andseries impedances in one correspond to bridged impedances in the other.

An important advantage of the filter 19 as a coupling between the space discharge tubes 37 and 45 is that, being substantially non-reactive, the tendency for the amplifiers to establish parasitic oscillations or singing in the system is greatly reduced. y

It is to beunderstood that the invention herein described .is capable "of gene-ral application and is not to be limited to the claims.

specific embodiments disclosed but only-as indicated by the scope What is claimed is: v Y Y 1. In a wave transmitting system, a wave source, a load circuit, and a filter network connected'between said source and said circuit, said filter network comprising two sep- 1arate filters for transmitting ,waves mdepepdentlybetween said source and said c1rcuit, said separate filters being complemenv tary' asg'regards their reactance'.

2. In a wave transmittingsystem a source `of complex waves, a wave tfilter connected thereto and including .reactive impedance elements, and a load circuit connected to the output terminals of said wave filter, said filter comprising two portions included in separate wave channels, said portions being complementary with respect to their impedances and including resistance elements of the appended whereby the impedance of the system to waves from said source is made a constant resistance at all frequencies.

3. In an nterrupter circuit, a source of waves, including an interrupter, a load circuit., a plurality of filters arranged to transmit in parallel between said source and said load circuit, said filters being complementary, whereby their combined impedance to waves of all frequencies is substantially,

constant and non-reactive.

4. In4 an electric wave vtransmission sy:-

tem, a source of waves, a load device, a resistance connected to said source, and a filter terminated by said resistance, said filter comprising a plurality of component filter networks, each terminated by independent portions of said resistance, said filter as a whole being substantially non-reactive. 5. An electric wave transmission system in accordance with claim 4, characterized in this that said independent portions of said resistance are equal.

6. ln an electric wave transmission system, a. source of waves, a load device, a resistance in two equal parts R, and R2 connected to` said source anda broad band filter ferminated by said resistance, said lfilter comprising two component filter networks terminated respectively in the parts R, and R2 of said resistance, the first component filter having series elements' of impedance Z1l and shunt element-s of impedance Z2, and the `other component filter having series impedance elements Z1, and shunt impedance elements Z22 said lters beingso designed that 7. 'A wave transmission networkscompris- GEORGE H. STEVENSON.

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