US1668725A - Telephone transmission - Google Patents

Description

TELEPHONE TRASMISSION Filed Sept. 28. 1921 gy@ S/ k Patented May 8, 1928.

UNITED STATES FREDERICK WHITTLESEY MUKOWN, OF NEW YORK,

, ELECTRIC COMPANY, INCORPORATED,

NEW YORK. i

N. Y., ASSIGNOR T WESTERN' OF NEW YORK, N. Y., A CORPORATION 0I TELEPHONE TRANSMISSION.

application med september as, 1921. serial No. 503,755.

This invention relates to telephone transmission.

Experiments have shown that the voice frequency range can be divided into parts 'l each of which will give a commercial degree of articulation. One object of the invention is to utilize the principle involved in this discovery for satisfactorily repeating voice currents in oppositedirections in a v line without regard to conditionsof impedance unbalance in the line. Another object of the invention is to utilize this principleto enable a plurality of pairsof subscribers to talk over the same pair of lines l5 simultaneously.

'Ihe first of these objects is accomplished by transmitting only a part of the voice frequency range in one direction and transmitting the remainder, or a part of the remainder, in the opposite direction, each of theseV arts being sufficient to represent intelligi le speech. `This method makes it possiblej to employ 'frequency separation of the oppositely directed transmissions at the repeaters, so that the gain of the repeaters is limited not by considerations of line imedance or impedance unbalance, but only y the efficiency of the filtersor other means used to effect the frequency separation, and

furthermore, the necessity for the balancing networks ordinarilye employed in `other sys tems is avoided.

To accomplish the second object' stated above one duplex conversation is limited to an intelligible part only of the voice frequency range, transmission in both directions over a line using this part of the range, and the remainder of the range, or a part of the remainder, is used to transmitscription and the appended claims taken in,

connection with the accompanying drawings wherein Fig. 1 is a diagram of a repeating system employing entirely distinct repeatover the same line a second duplex conversa.-`

ing channels for oppositely directed trans- `missions, `with amplifying elements individual to the two channels; Fig. 2 is a diagram of a modified repeating system using an amplifying element arranged to serve both channels; Fig. 3 is a dia am sim1lar to that of Fig. 2, but with lters connected. inv parallel rather than in series as 1n Fig. 2; and Fig. 4' is a diagram of a multiplex telephone syste In Fig. 1 a line W and a line E are connected by] a repeater station S comprising filters F and FW and amplifiers or repeaters RE and RW. Supposing a voice current containing all of the usual frequencles of the voice range to approach station S from line W, at the station S it enters the output of amplifier RW and the input of filter FE. The energy absorbed in the output of the amplifier RW is of course lost.

Approximately one half of the frequencies are suppressed in filter FE, which may be of any suitable type, but the other half reaches the input of amplifier RE and are amplified thereby. The amplified current goes onto the line E after passing through the impedance looking into the input end of filter FW, which may be of any suitable type and should be designed, as for instance in a way indicated hereinafter, tively low for these frequencies. The filter FW is designed to suppress these frequencies to prevent them from reaching the repeater RW. The current reaching linerE then only contains a part of the frequencies which left line lW, but the received frequencies are sufficient for satisfactory transmission of speech.

The operation of transmitting from line E to line W is of course the same except that-.

to be comparathe transmission is through lter FW and amplifier RW and the filter FW passes only `those frequencies which are not passed by filter FE.

Various distributions of frequency bands may be employed. For instance, the filter FE may be designed to suppress all voice frequencies above 1500 cycles per second, l and the filter FW to suppress all voice freuencies below 1500 cycles or vice versa.

r one of the filters may suppress from 500 to 900 cycles and all voice frequencies above 2000 cycles while the other filter is designed to suppress from 0 to 500 cycles and from 900 to 2000 cycles. Or one of the filters may suppress from 300 toOO cycles, and from 1100 to 1600 cycles an all voice frequencies above 2700 cycles while the other filter suppresses from 0 to 300'cycles, and from 600 to 1100 cycles and from 1600 to 2700 cycles.

Tests indicate that the articulation is materially increased when the more elaborate complementary filters are used instead of merely a high pass filter and a low pass filter. The number of frequency bands to used in each group, or in each channel, is limited at the lower side by the required degree of naturalness and articulation and at the u pper side by the fact that more bands require more complicated filters and cause increased losses, due to the overlapping of the attenuation bands of the filters in one channel with the attenuation bands of the filters in the other channel.

The repeater circuit of this invention requires no impedance balance, and permits of greater transmission gains than .do circuits in which the gain is limited by considerations of impedance unbalance. The system is not aected by any irregularities in line impedance. An important 'field of application of the invention is in its use in a cord circuit v repeater between trunks having irregular im- \pedance characteristics or in an emergency cord .circuit repeater in an exchange for connecting'trunks in which temporary impedv 3: ance irregularities have been introduced accidentally. Another important field of appli cation of the invention is in its use in connecting trunks which are not intended for repeater operation, over which it is at times desirable to give repeater service. Still another importantfield of application of the invention is in its use in repeating 'in long temporal` lines, as for instance` in Army wor The permissible gain in volume of ,transmission obtainable in any case depends y wir the minimum attenuation of the filter or FE for the fr uenciespassed by the filter FE or the filter W, respectively.

If desired the impedances looking into the West ends of the two separate channels at the repeater station S in Fig. 1 can be connected to line W in parallel with each other rather than in series. Similarl the im edances of the two channels, Jlookin into t eir East ends, may be connected in parallel. Further, if desireda art of the lter .in each channel can be placed ateach side of the mpler in that c annel, the filters hav- *ing been shown wholly on the input side of the amplifiers for the reason that there is then lesstendency to overloading ofthe amplifiers.

Fig. 2 shows a circuit arrangement whereby both channels at the re eater station are served by the same amp Filters 1 and 2 are alike, and each may be of any of the types of filters which are intended to be represented by FE in Fig. 1. Filters 3 and 4 -are alike, and each may be of any ofthe types of filters which are intended to ibe re resented by FW in Fig. 19 Theflters 1 anh 2 may transmit any part of the voice frequency ranffe which any of the filters represented by FE in Fig. 1 may transmit, and the filters 3 and 4 may then'.

transmit the remaining part of the voice frequency range.

In the operation of the system of Fig. 2, when 4a voice current containing all of the usual frequencies of the Voice range is bein L transmitted East in line W, this curren asses from line W through the impedance ooking into the output of filter 4, and to the input of filter 1. Filter 1 asses only approximately one-half of these requencies. Filter 4 passes the other half, but the ener of this other half is wasted in the imp ance looking into the output of repeater R and the impedance looking into the input end of filter 2, since the repeater is unilateral current transmitting element and the filter 2 i's designed to suppress this other half of the voice frequencies. The frequencies passed by filter 1 pass on through the impedance looking into the output end of filter 3, to the input of amplifier R, are amplified by the amplifier and are then'passed through the impedance looking into the input end of filter 4, and through filter 2 and the impedance lookingdnto the input end of filter 3, to line E. ilter 3 will not pass these .frequencies. The impedances looking into the output end of filter 4, the output end of lter 3, the input end of filter 4 and the input end of filter 3 should be designed, as for instance in a way indicated hereinafter, to be low for these frequencies. The operation of transmitting from line E to line W is of course the same, except that the transmission is through filters 3 and 4 instead of through filters 1 and 2, and the filters 3 and 4 pass only those frequencies which are not passed by filters 1 and 2.

In Fig. 3 two oppositely for transmitting complementary Vfrequency ranges are both served by the saine amplifier R, as is the case in the system of Fig. 2. Each of the filters F, and F1 of Fig. 3 transmits the same part of the voice frequency ran e that! fi ters 1 and 2 of Fi 2 transmit. transmits the saine part of the voice freach of the filters F2 and z" iio directed channels'l quency range that filters y3 and 4 of Fig. 2

transmit.

In the operation of the system of Fig, 3,

when a voice current containing all of the er, designated R. and the output of filter F, v in parallel.

l t e repeater and passed of these Lacanau y Filter F, asses only aplproxiniately one half proxima-tely one hal equencies. ilter F2 passes the other half, but the energy of this other half is wasted in the output of repeater R and ,the impedance looking into the input end of filter F,, since the repeater is a unilateral current transmitting element and the filter F is designed to suppress this other half of the volce fre uencies. The freuencies passed by filter through filter F,' to line E. The filter F2, like the filter F2', will not pass these frequencies. The impedances looking into the input end of filter F2', the output end of filter F, the outtput end of filter F2 and the input end of lter- F2 should be designed, as for instance in a wayindicated hereinafter, to be high for these frequencies to avoid 4large losses at these fre uencies. The operation of transmitting rom line E to line W is of course the same as that described for transmission East, except that the transmission is through filters F2 and F2 instead of throu h filters F, and F,', and the filters F2 and 2 pass only those frequencies which are not passed by filters F1 and F,'. In Fig. \4 a line L serves for duplex transmission of vo'ice currents between lines L,W and L,E and at the same time for duplex transmission of voice currents between lines LZE and L2W. In order to accomplish this result, filters AF AF,' AF and AF2 are inserted in lines L,W, L,E, ll2E and L2W, respectively, these filters being similar to the correspondingly designated filters F F1', F, and F2', respectively, of Fig. 3, but having their terminal reactance elements at those ends of the filters which are the more remote from line L consisting of a series arm the impedance of which is, as usual, half the impedance of a full series arm.

In the operation of this system, when a voice current containing all of the usual voice frequencies ori inates in line L,W apof these frequencies is suppressed b filter AF,. The other half is transmitte throuvh filter AF line L and filter AF, to line ,E. Filters AF2 and AFa exclude the latter frequencies from lines L2W and L2E respectively. The impedances looking into the output end of filter AF2' should be high forthese frequencies to avoid large losses at these frequencies. The frequencies which filters AF, and AF, are designedto passare of course also excluded from lines L2E and L2W by the filters AFz and AF2', respectively, when' these frequencies are being transmitted from line L,E through filter`AF,, line L and filter AF, to line L,W. i l

When a voice current containing all ofl Vthe usual voice frequencies originates iin line L,W approximately one half of these are amplified by4 FE be made low and the input end of filter AF,`

frequencies is suppressed by filter AF,'. The other half is'transmitt'ed through filter AF2', line L and filter AF2 to line L,E. Filters AF, and AF, exclude the latter fre uencies from line L,W and L,E, respec-V tive y; The impedances looking into the output ends of filters AF1 and AF,' should be high for these frequencies to avoid lar'ge losses at theseV fre uencies. The frequencies which filters F2 and AF2' are designed to pass are ofcourse also excluded from lines L,E and L,W by the filters AF,' and AF, respectively, when these frequencies are being transmitted from line L E through alter AF2, une L and alter AFO in series instead of the impedances looking into their West ends being connected in parallel and the impedances looking into their East ends being connected in parallel as are the corresponding impedances of filters AF, and AF2I in Fig. 3. The'filters AF2 and AF,' in Fig. 4 may have the irnpedances looking into their West ends connected either in series or in parallel, regardless of Whether the filters AF2 and AF,' have the impedances looking into their West ends connected in parallel for in series.

The impedance looking into the input of filter FW of Fig. 1 may be madelow for the frequencies passed by filter FE and the impedance' looking into the input of filter for the frequencies passed by filter FW, by 4properly terminating these filters at their input ends. For instance if FE be a low pass filter suppressing all frequencies above 1500 and FW be a high pass filter suppressing all frequencies below 1500, then assuming each of these filters to be made up of, for instance, a plurality of sections each section of filter FE consisting, say, of a series inductance element and a shunt capacity element after the fashion of the filter of Fig. 7 of U. S. Patent to G. A.

Electrical receiving translating, or repeating circuit, and each section of filter .FV

consisting, say, of a series capacity element and a shunt inductance element after the fashion of the filter of Fig. 6 of the Campbell Apatent mentioned above, then the first section of high pass filter FW may be made 'to begin with a shunt inductance element having` an` impedance which is 10W for the frequencies passed by low pass filter FE, and the first section of low pass filter FE i mentioned above, and filters 3 and '4 to then be high pass filters suchas that of i;

of the Campbell patent, then each en high pass filters 3 and 4 may be terminated in a shunt inductance element of low impedance for the frequencies passed by low pass filters 1 and 2, and each end of low pass filters 1 and 2 maybe terminated in a shunt condenser of low `impedance for the fre quencies passed by high pass filters 3 and 4. Y It will be clear that when one end of a low pass filter is connected in parallel with 4one end of a high pass filter, as for instance in providing a system such' as is shown in Figs. 3 and 4, then the one end of the high pass' filter may be made' to begin with a series condenser having high impedance vfor` the frequencies passed by the low pa`ss filter,

susv

- of the and the one end of the low\pass filter may be made to begin .with a series inductance element having high impedance forl the frequencies passed by the hi h pass filter.

Preferably where it is esired to connect a high ass filter such as is shown in Fig. 6 Campbell atent referred to above in parallel with a ow pass filter such as is shown in Fig. 7 of that patent, for separating currents into two channels, the filters should have4 approximately the same cut-off fre uency and, using the symbols employed in t e patent, Z1, Z2 should be constant with L2 varymg frequency and C: should be equal to L1 2 nated with a series condenser having a value of approximately 1.25 C at the end which is to' be connected in parallel with the second filter and the second filter at the corresponding end should be terminated in a series reactance coil having an inductance of .8 L1. If the ends of the filters are to be connected in series the first filter should end in a shunt element having an inductance of 1.25 L, and the second should end in a shunt element having a capacity of .8 C2. If this is done the impedances of the filters will be such that the combination will have a practically constant impedance at all frequencies except in the immediate vicinity of the cutolf fre uency and neither filter will interfere deleteriously with the operation of the other. The principles and reasons underl in this design of the filters are set forth 1n etail in the United States Patent to Otto J. Zobel,'No. 1,557,230, dated October 13, 1925, entitled Complementary filters, issued on pplication Serial No.377 ,965, filed April Then the first filter shouldbe termi.

' s mesma In a similar waywhen a multi-band filter l lto above the impedance of the series arm multiplied by the im edance of the shunt arm should preferab y be constant at allr frequencies and the filter should preferably be terminatedin a series section having approximately times the impedance of the full series section if it is to be connected in parallel with a complementary filter or in a vshunt section having approxi- 4mately .1.25 times the impedance ofthe full shunt section if it is to be connected Kin series with a complementary filter. A

method ofdesignin a wave filter in which the impedance of t e series armmultiplied by the impedance of the shunt arm is constant with? varying frequency, and `which will transmit over any preassigned number ofl frequency ranges is disclosed in United States Patent to Zobel, No. 1,509,184, dated September 23, 1924, entitled Multiple band wave filter, issued on application Serial No. 377,963, filed April 30, 1920..

AAs noted above, a part of the filter in each channel'in Fig-1 can be placed at each side of the amplifier in .that channel after the general fashion in which the filtering means 1 and 2 inFigs2 is placed partly at-each side of the amplifierl Then the resultant ofthe impedances looking from line W into the two channels, and theresultant of the impedances looking from the lou line E into the two channels may be madel practically constant at all fr uencies except in the immediatevicinity o thacut-o frequencies, in the manner explained above.

What is claimed is:

1. Thev method oftreatin telephonie messages simu taneously impressed upon the line, each as a group of alternating currents in the voice frequency range, .which comprises separating at the receiving end of the line groups of currents each of which groups represents one of said messages, and one of which oups consists of currents of frequencies lying outside the limits of the frequencies of the currents in another of said groups.

2. The method of operating a repeater having oppositely directed unilaterally repeating paths which comprises transmitting in one of said paths voice currents of frequencies limited to part of the voice frequency range, and transmitting in the other of said paths voice currents of frequencies limited to the remainder of the voice frequency range.

' 3. -A system for repeating voice frequency currents, comprising aline and a two-way repeater circuit including transmission aths, selective of voice currents of certain requencies, for frequency separation of opa number of'- pitely directed voice frequency currents transmissions from each other.

4.' In a voice frequency telephone system, the combination with two llne circuits for transmitting voicel currents,I of a two channel connect-ing circuit for transmitt' voice frequencies inF opposite directions, sai two channels havinga common transmitting portion and `being simultaneously in con; dition to transmit between said two lines.

5. In a voice frequency telephone system, the `combination with two line circuits for transmitting voice currents, of a two channel connecting circuit for transmitting voice frequencies in opposite directions, said two channels having a common unilaterally transmitting ortion normally connected for transmission 1n each direction between said line circuits.

6. A line for transmitting a pllurality of voice current waves of substantia y different voice frequencies in each direction, a second similar` line, and two-way repeating means capable of repeating said waves simultaneously without mutual interference between said lines, said means com rising a single am lifyingfpath associate with both of sai lines. i

7. Two lines fortransmitting voice frequency currents in both directions, and an am lifier having an input circuit coupled to bot of said lines, and an output circuit cou- \pled to one of said lines through a path selective of certain voice frequencies and to 35 the other line through aa pathselective of only other voice frequencies.

v8. Two lines for the transmission of voice frequency currents in both directions, a oneway selective path between said lines for transmitting voice frequency currents having certain characteristlcs, another one-way selective path between said lines for transmitting in the opposite direction only voice frequency currents of characteristics different from the first mentioned characteristic and a single amplifier common to both sai paths'. p

9. Two lines for the transmission of voice frequency currents in each direction thereover, the voice currents transmitted through bothof said lines in one direction -having different characteristics from those transmitted through both of said lines in the opposite direction, an amplifier for amplifying all of said currents havingI its input and its output circuits each common to both of said lines, anda yplurality of selective. paths in said output circuit between said amplifier and each of said lines for selectively transmitting said currents.

10. Two lines for the transmission of voice current waves in each direct-ion thereover the voice current waves transmitted over both of said lines in one direction having respectively' different characteristics from those opposite direction, an am lifier for all of said waves, an input circuit and an output circuit each having two branches one for each line, and lilteis in each of said branches.

11. A line, a two-way repeater in said line comprising a circuit for transmission of voice frequency currents in one direction, and another circuit for transmission of currents of other different voicev frequencies in the opposite direction, an amplifier in one of said circuits, another amplifier in said other circuit, and selective means in one of said circuits for selecting the frequencies used in transmitting in one direction, and selective means in the other circuit for selecting the frequencies used in transmitting in the opposite direction.

l2. In a telephone system, transmission line sections, one-wa transmission paths interconnecting said ine sections, and`selective means whereby only a portion of the voice frequencies approaching said paths from one direction over said line sections will pass over one of said paths, and whereby o the voice frequencies approaching said paths from the op osite direction only frequencies different rom those passed by said one path will pass over the other of said paths. v

13. In a telephone system, transmission line sections, one-way. transmission paths interconnecting said line sections,.oneway repeaters in each of said paths and selective means in one of said paths whereby only a portion of the voice frequencies approachmg said paths over said line sections 1n one direction will pass over said one path, and se-V lective means in the other path whereby of the voice frequencies'approaching said aths over said line sections in the opposite direction only fre uencies different from those passed by sai one path will pass over said other path. A

14. A channel comprising a band filter for transmitting voice frequencies lying between certain limits, a second channel comprising a second band filter for sup ressing frequencies between said limits, eac filter being capable of passing voice currents representing intelligible speech, and a line having one end connected to one end of the first mentioned channel and to one end of said second channel, the impedance of said second channel looking from said end of said lineand said end of said first channel being of such value for the frequencies passed by said first chan' nel that the volume loss in transmission due to said 'im edance is small for frequencies transmitte through said line and said first filter. l

15. A common transmission path, a plurality of'channels each adapted to transmit currents of different frequency from those transmitted by the other channels, and s transmitted over bothof said lines in the ico separate .band filter transmitting voice quencies" connectin each channel to vsaid path the terminations of said filters elecjacent said path being connected in parallel.

16. A common transmission path, a plurality of channels each adapted to transmit currents of different frequency from transmitted by the other channels, and a separate band lter capable of' passing voice currents re resent'ing intelligible speech connecting eac channel to said path,.the terminations of said filters electrically adjacent said path being connected in parallel.

17. A circuit a plurality of voice current channels assoclated therewith, means :for

, transferring voice currents of different voice frequencies between said channels and saidv circuit, said means comprising an individual lter connected to each of said channels, the transmission range of each fltervbeing distinct and being such as to permit p e of voice currents representin intelligib e speech, said filters having termmations connected in parallel to said circuit, the termina tion of each filter having a high impedance Vfor currents of the transmission frequency Vrange of any other filter whereby said filters do not short-circuit each other.

30 18. A common transmission path, two

and a second filter capable of 1passinghvoice n e speec concurrents representing mtelligib necting the second of said channels'to said a different .range of' voice path, each of said filters comprising sections aving shuntand series arms, ea'ch filter being terminated in a series arm having approximately .8 times the impedance of a full series arm, 'and the terminations of said filters being connected to said path in parallel. 19. The method of two-way telephone transmission of speech currents over the same line com rising transmitting in one direction over sai line currents in the ordinary/speech fre uency 'range confined to frequencies hig er thanA a given limiting frequency, and transmitting in the opposite direction over said `line currents in the ordinary speech frequency range confined to frequencies lower than said given limiting frcquenc In witness whereof, IA hereunto su scribe my name this 24th day of September A. D.,

FREDERICK WHITI'LESEY McKOWN.

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