US1537106A - Means for and metho of equalizing attenuation - Google Patents

Description

yMay 1'2, vv'1925.

' H. A. AFFEL MEANS FOR AND METHOD 0F EQUALIZING ATTENUATION Original Filed June 2, 1921 n TSQNSQ MHQHWWHH..

IMWMH HHEWMHM Patented May 12, 1925.

UNiTED s'rii'rlassfA PATE- 1,537,106 A orinar-1.".

HERMAN A. Armer., or BnooxLYN, NEW Yoan, AssreNon rro AmnnrcAN TELEPHONE AND TELEGRAPH COMPANY, `A Conroe-Arron or NEW Yonx.

l MEANS FOR AND METHOD OF EQUALIZING ATTENUATION.

Application led June 2,' 1921, Serial No. 474,402. Renewed August 6, 1924.

Ta all whom it may concer/n.:

Beit known that I, HrlinnANt A. AFFEL, residing atBrooklyn, in the county of Kings and State of New York, have invented certain Improvements in Means for and Meth? ods of Equalizing Attenuation, of which the following isa specification..

This vinvention relates to the transmission of alternating currents for signalling or other purposes, and more particularly to the equalization ofthe attenuation of the currents transmitted over a circuit at different frequencies.

It is a well known fact that when variable currents such as telephone or telegraphfcur.-

rents are transmitted over a long conductor, distortion' occurs owing to the difference in the attenuation of the .different frequencies involved in the transmission, the higher frequencies being subjected to greater attenuation than the lower frequencies. This is particularly undesirable in the case of telephone transmission, as good quality of speech transmission requires that the wave form of the signal initiated at one end of the line must be maintained at the receiving end, and when the distortion becomes serious, the transmission tends to become unintelligible. In accordance with the present invention (it is propesed to overcome this diliiculty by tras' mitting the telephone or other signalling band in its normal condition over one half of the entire length of a transmission system, and transmitting the band inverted over the other half of the system. In `other words, overv one half of the circuit the voice band is transmitted in such a manner that the -frequency relations of the band are normal, while overl the other half of the circuit the fre uency relations are inverted so thatxthe higher frequencies of the voice band become low frequencies, and the lower fre uencies become high frequencies. The hal 'of the total system over which the voice currentsl are transmitted at their normal frequencies gives the usual rising frequency-attenuation curve; thesecond half of the system has'a similar frequency-attenuation characteristic but the frequency band, being reversed, in effectreverses the attenuation curve itself. For example, if a frequency of 2,000 cycles in the normal portion lof the system translated-to 200 cycles in the inverted portion, the total attenuation suffered by the 2,000

by a 200 cycle component,`which in the inverted` half of the system appears as 2,000

cycles.

In order to invert the band when desired and to restore it to normal for receiving purposes, advantage is taken of the principle of -modulation whereby as a`result of modulating a carrier frequency by a transmission band, two side bands will result on either side of the carrier, each side band having the same 7width as the transmission band, and one' side band having the same frequency relations as the original bands, but the other side band -l l having the frequency relations reversed. If the carrier .be so chosen as to correspond to the upper frequency of the normal voice band, the .lower side band resulting from modulation' will be reversed with respect to the normal voice band, but will occupy the 'same frequency range.

The invention "may now be more fully understood by referring to the following detailed description when read in connection with the' accompanying drawing, Figures 1, 2 and 3 of which represent three schematic embodiments of the invention.

Referring to Figure l, L'1 and L4 designate telephone4 circuits, incoming to stations A and' B, to which voice currents or other signalling currents'may be applied for transmission between stations A and B, said stations being interconnected by line sections L2 .and L3, over which it is desired to equalize the attenuation. In order to equalize the attenuation the circuit is so arranged that in transmitting from station A to station B, the frequency relations of the voice band will be inverted in transmitting over the line secfor transmission from station A over the` line section L2, the line section L1 is asso-l ciated with the line section L2 at thestation A through a circuit arrangement having the general form of a 22 repeater circuit, com prising channels E, and W1, the channei E, being used fortransmission from west to east,

.cycles per second,it

and the .channel W1 from east to west. The channel E3 is provided with amodulating apparatus M3 w ich may be of any well known type, such as for example, a vacuum tube modulator. The modulator is supplied `with is arran ed to select the lower side band re- -Ez and `ficial lines or networks N3 sulting rom modulation. For this purpose,` the band filter is designed to have an upper l cut-olf frequency of 2,000 cycles. It will be understood, of course, that the line sections L1 and L3 will be balanced in the usual manner by means of artificial lines or networks N3 and N3. s

Similarly at station B a 22 circuit having channels1E3 and W3 is provided for interconnecting the line sections L3 and L,3 and inverting the band transmitted fromy east to west. The line sections L3 and L,3 arebaL' anced with respect, to these channels by means of networks N3 and N4 respectively, and the channel W3 is provided with a modulating arrangement M3 and a band filter BF3 similar to the modulating apparatus and band filter in the channel El'at station A.

At an intermediate point C a 22 form of circuit or anization is arranged to interconnect the line sections L3 and L3 for vthe purpose of reinverting the inverted bands transmitted to this pointfrom the terminal stations so that the bands may be transmitted from this point to'the terminal stations in. thenormal frequency relation. The circuit organization 'at station C comprises channels connected as indicated, the artiand N3l being provided to balance the line sections L3 and L3. Modulating apparatus M3 and M3 is included inthejchannels E3 and W3 respectively, this apparatus being similar tothe modulating apparatus already` described. Band filters BF3 and BF3 are also included in the output circuits of the modulators, these band filters being similar to the band filter at station A.

Further detailsfof the apparatus will be acquired from the description4 of the 0peration, which is as follows: Assuming that a band of voice currents is to be transmitted fromthe station A tothe station B, the band of frequencies-willpass from the line section L1 into the channel E1 to modulate the carr1er frequency of 2,000 cycles, which coincides with the upper limit of the voice band. In orderto understand the operation more clearly the processes to which one frequency in the voice lrange is subjected in passing from station A to station B will be consid# lower limit of condition,

ered. A frequency of 200 cycles, 'for example, in passing into.v the modulator M1 modulates the carrier frequency of 2,000 cycles to produce frequencies of 1,800 cycles andV 2,200 cycles. The-u per frequency is eliminated 'by theband lter BF1 and the lower frequency of 1,800 cycles passes to the line section L3 and .over said line section into the channel E3 at station C. It will be observed that during transmission over the line section L2 the frequency relations are inverted and the frequency of 200cycles which'normally lies near the lower side of the voice band is translated to 1,800 cycles, which is correspondingly near the upper limit of the voice band. When the^1,800 cycle frequency passes intothe modulator M3 at station C it modulates the carrier frequency of 2,000 cycles to producefrequencies of 200 cycles, and 3,800 cycles respectively.y The upper of these two frequencies is eliminatedby the band filter BF3 and the 200 cycle frequency,` which it will be noted is nowA restored to normal condition, is transmitted over the line section L3 and passes Jthrough the channel E3 to the line section L3, at station B. It will be readily apparent that the voice 'band was inverted during transmission over the'line section L3 and was reinverted and transmitted over the line section L3 in normal so that on the average all fref quencies were subjected to substantially the same attenuation.

The vtransmission from station B to station A is similar `to that already described. A frequency of 200 cycles incoming from the line section L3 passes through the modulator M3, is translated to a frequency of 1,800 cycles and after transmission over the line section L3 is translated by the modulator M3 tothe normal frequency of 200 cycles, which in turn is transmitted over the line section L3 and through the channel W1 to the line sectin L3.

Figure 4 indicates schematically an arrangement for obtainingthe same result by means of a four-wire. circuit extending between station A and B. 'For' transmission from west4 to east, the line sections L1L and L7 at stations A and B respectively are interf connected by a transmission line com risverting apparatusis provided between each of the other line from west t-o east, and the circuit used 1n transmitting from east to west is also prosections used in transmitting vided with band inverting apparatus at the junction point of each line section.- 'The circuit asthus arranged will result in normal transmission over the line sections -marked Normal and inverted transmission over the line sections marked linverted. If line sections 'L2 and L2 as Well as line sections L5 and L5', are made of onehalf the length of the other lline sections, the other line sections being made of equal length, it will be apparent that the telephone band will be transmitted inverted over onehalf of the distance between A and B and will be transmitted normal during the other half. The same result may, of course, be obtained by making the line sections unequal, but in this case it is desirable that the total lengths of the sections transmitting the band inverted be substantially equal to the total lengths'of the sections transmitting the band in normal condition.

Assumin a band. incoming rom the line L1 is to. be transmitted to station B, the band will be transmitted over the half line section L2 where, by modulating with a carrier frequency of 2,000 cycles, and by suppressing the upper side band, the band will be inverted for transmission over the section L3. The in verted band, by'means of the modulator M1, and band filter BF2, will in tunn be reinverted and transmitted in normal frequency relations over the section L4. It is again inverted by the apparatus M4 and BF, and 'transmitted with the frequencies in inverse relationover the section L5, after which it is restored to normal' by the modulator M5 and the band filter BF5 and transmitted in normal condition to the line L?, The trans- ,inission in the opposite direction is similar, the band being transmitted in normal condition over the line section L5', inverted and transmitted over the line section L5', rein- `vert'ed and restored to normal for transmission over. the line L4', again inverted for v transmission overthe vline section L2', and

finally restoredto normal for transmission over the line section L2.

' A somewhat similar arrangement is illustrated in Fig. 3, this figure diffe-ring from that of Fig. 2, however, in that the carrier frequency, instead of being'supplied locally at each -modulating point, is transmitted along with the telephone band or inverted band, as the casemay be; fqrexa1nple, for transmission fromwest toeast the carrier frequency is supplied at the terminal station A from" a3' source Sland is transmitted with the normal band tothe modulator M2,4wh'ere the telephone band modulates-with the carcrie'r frequency to invert the band in'the samemanner as in the case ofl Fig. 2.? The` modulating apparatus must in this instance be of a type which does not sulppress the carrier, whereas in the case of 1g. 2, the

f telephone frequenciesto west, the carrier will be supplied by the.

source S7 at station B and transmitted with the normal or inverted side band as the case may be, just as described in connection with ,transmission from west toeast.

It will be evident that the method above described involves a form of carrier system. For the sections in which the band is invertalternating current whose frequency coincides with the upper limit of the telephone or signalling band, while in sections in which the band is transmitted normal, the carrier or reference frequency is a zero frequency. In inverting the telephone band, it will be advantageous ordinaml to keep it ed the carrier. or reference frequency is an l vas low in frequency as possi le, thereby causing the inverted band to occupy substantially the same position in the broad frequency range as does the normal band. It will be evident, however, that the inverted cband may be made to occupy any position in the broad frequency range and that in fact both the inverted and non-inverted ordinary carrier rv'nels as it is for channels operated at ordi-v nary signalling frequency. Verylong carrier circuitsmay, however, warrant inverting the band for ualization purposes. A convenient way o inverting the carrier bands obtains in a system employing opposite side bands referred to the carrier .frequency for transmission east and west respectively. For example,l if the common carrier is 10,000 cycles, and one channel operates onthe upper band up to 12,000 cycles, and the oppositely directed channeloperates von the .lower band down to 8,000 cycles, these bands may be readily interchanged at a repeater point 'by being modulated in a common modulator, if desired, with 10,000 cycles.

l It will be understood that in the previous description the various frequencies referred to', and the apparatus described, is for puroses of illustration only, and the invention applicable tofotherfrequenc ranges and withlother forms of apparatus than those referred to in the description and illustrated in the drawing.

It will also be obvious that the general principles herein disclosed may be embodied in many other organizations widely different from those illustrated without departing from the spirit of the invention as defined in the following claims.

What is claimed is:

1. The method of equalizing the attenua manner lduring transmission over the remainder of the system.

2., The method of equalizing the attenuation of a band of frequencies transmitted over a transmission system which consists in transmitting the band in normal frequency-7 relation over a portion of the system, and transmitting the band in an inverted frequencyv relation and in the same frequency range over the remainder of the system.

Y 3. The method of equalizing the attenuation of a band of frequencies transmitted over a transmission system which consists in transmitting the band over a portion of the system in normal condition, modulating the band with a carrier frequency, thereby producing side bands, selecting the lower side band which correspondsto the original band inverted,'fand trasmitting the inverted Aband over another fportion of the system.

4. The method o equaliing the attenuation of a band of frequencies transmitted over a transmission system which consists in transmitting the band over a portion of said system in normal-condition, modulatin the band withl a carrier frequency in the neighobrhood of, the upper limit of the which corresponds to the original band with frequencies inverted and transmitting the inverted band. overc another portion1 of the system. f n f g 5. A system for (the equal attenuation of a-band of transmitted frequencies comprising a system of'conductors over Which the band is transmittedl in normal frequency relation, means for inverting the frequency relation of the band, and applying it to a similar system of conductors so` that it will be transmitted over the second system of conductors in inverted frequency relation.-

6. A system for the equal attenuation 'of a band of transmitted frequencies comprising a system Aof conductors over which the band may be transmitted in normal frequency relation, means for modulating the band in accordance with a carrier frequency,

thereby producing side` bands, means to select the lower side band corresponding to theloriginal band in inverted frequency relation, and to impresssaid inverted band upon a second similar system of conductors, whereby-the band may be transmitted over the second system of conductors in inverted frequency relation.

7. A system for the equal attenuation of a band of transmitted frequencies comprising a system of conductors over which a band of frequencies maybe transmitted in normal frequency relation, means for modulating said band of frequencies with a carricr whose frequency corresponds substantially to the upper limit of the transmitted hand, thereby producing side bands, means for selecting the lower sidle band corresponding to the original band in inverted frequency order and impressing said inverted band upon a second similari s stem of conductors, so that the band may e transmitted. over said second system of conducl tors in inverted frequency relation.

8. The method of compensating for the distortion in Wave shape produced by transmitting a band of signaling frequencies over a transmission system, which consists in transmitting the signaling frequencies in normal frequency relation over a portion of the circuit to produce distortion of one character and transmitting said frequencies in inverted frequency relation and in the same frequency range over the remainder of the system to produce distortion of a complementary character.

9. A system for compensating the distortion resulting from the transmission of a band of signaling frequencies over a transmission system, said system comprising conductors overA which the currents are transmitted in normal frequency relation to produce distortion of one character, and means for inverting the frequency relation of the signaling currents and applying them to a.

similar system of conductors so that distortion of a complementary character with 4l1aei" May, 1921. y

- vHERMAN A.

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