US1644395A - Transmission system - Google Patents

Description

Oct. 4, 1927, 1,644,395

B. G. POHLMANN TRANSMISSION SYSTEM Filed May 29. 1926 atente Get. 4, l2?.

BRUNO G. POHLMANN, F SIEMENSSTADT, NEAB BERLIN, GERMANY, ASSIGNOR TO SIEMENS & HALSKE AKTIENGESELLSCHAFT, OF SIEMENSSTADT, NEAR B l It',

GERMANY, A CORPORATIVIION 0F GERMANY.

TRANSMISSION SYSTEM.

Application filed May 29, 1926, Serial No. 112,419, wand, in Germany May 14, 1925.

This invention relates to electrical transmission systems and has for its general ob'- ject to compensate for the distortion produced by a long transmission line.

5 As is well known. the distortion of long telephone lines is eliminated either by using repeaters having amplification characteristics proportioned to compensate for the line distortion o1' by inserting correcting artificial lines having attenuation characteristics complementary to the attenuation of the line in combination with repeaters having substantially flat amplification characteristics. In both cases an overall characteristic which is independent of frequency is desired. Generally the line is divided 'into sections and the distortion in each section is corrected by the corresponding repeater or the equalizer associated therewith. In long.

transmission lines. which necessarily embrace a large number lof repeater sections, the demands made on the precision of correction at each individual repeater point are exceedingly high since any deviations from 25 the attenuation or amplification characteristic required, which `may be produced by slight inaccuracies in the correcting means, likely occur at each repeater in the same frequency regions and consequently are cumulative for the entire transmission system.

A particular obj ect of this invention is to overcome this difficulty. r

Therefore. in accordance` with one feature of the invention the-correcting means of the sections comprising the transmission system are made diiferent, the differences being such that the sections are complementary to each other giving an overall transmission characteristic which is substantially inde- 40 pendent of frequency.

tion in a system comprising a large number of sections, each of a group of sections is corrected to give an approximately constant 4 5 characteristic and there is associated with one section of thev group anadditional cor-- recting means having such a characteristic as to compensate for the combined discrep ancies of the group.

lf the transmission system is ofv such length that it embodies several groups of sections of similar design the yariations from the. desired characteristic in each group may be' cumulative in a similar manner as In a preferred embodiment of the inven-l the variations in the sections of each group so that it is desirable `to provide additional means to. compensate for the total. group inaccuracies within the system in the same manner as the total section inaccuracies are compensated in each group. If the system 1s of such length that itis desirable to regroup the grou s this method may be extended still furt er.

Since, from a design standpoint, itis desirable to keep the correcting means as unitary as possible, an attempt is made to adhere to this principle so far as possible without deviating' from the spirit of the invention. Thus-within a section, group, or system. all sections or groups but one can be similarly constructed, their associated correcting means rbeing so designed that an overall substantially constant characteristic 1s obtained. If correcting repeaters are eni ployed the repeaters can either be particularly designed so that ends upon the frequency in a manner diferent from the standard repeaters, or else a repeater of the standard type having s ecial associated'corr'ecting means can be use The spacing of the special repeater points is preferably so chosen that the net distortion over the portion of the line therebtween is of the v'same order of magnitude as is ordinarily corrected for with a single network.. In this way apractically complete correction is obtained, even with very gre-at lengths of line. without` extraordinary demands be ing made upon the correcting means at the special repeater points.

`A limiting case is the one in which the group lconsists of only two sections in which the errors of'correction are so displaced with respect to each otherthat they practically neutralize one another. A transmission system of a large number of sections is then comprised of mere groups of two sections each so that altogetherit'is only necessary to construct two types of correcting means,

except where with an extraordinarily` large lnumber of groups an elimination of systematic errors of correction is again necessary.

rlhese and other. objects, features and aspects of the invention can be more readily understood by reference to the following detailed descri tion of one particular embodiment of the invention in connection with the ldrawing in which:

the amplification deioo viii

Fig. 1 shows-graphically the attenuation and amplification characteristic of a single line'section and repeater.

Fig. 2 shows graphically the netdistortion in a group of corrected sections and Fig. 3 shows diagrammatically one embodiment of a transmission system according to this invention.

Curve b of Fig. l shows the attenuation characteristic of a single repeater section plotted against frequency, while curve s of the saine figure shows the amplication characteristic of a correcting repeater associated with the same section plotted against frequency. It will ybe noted that the deviationsrof the lamplification curve from the attenuation curve are fairly small giving a characteristic for a single sectionwhich is a proximately lconstant with frequency.l

urve b, of Fig. 2, however, shows the net equivalent curve for six repeater sections,

the inaccuracies in the six sections having added up to give a characteristic which is suiiiciently distprted .to disturb speech transmission.

Fi 3 shows a transmission system compose of six line sections 1, 2, 3, 4, "5 and 6' and associated repeaters, 11, 12, 13, 14,

and 16. Assumingth'atthe attenuation in each section is represented by the' curve b of Fig. 1, it has been found desirable for carrying `out this invention to design thereeaters to have an amplification characteristic s somewhat higher thansA which would beirequired for compensating for the attenuy ationl of a single section. This gives a total attenuation characteristic 'for the six sections as shown-by the curve b,. Associated with'the sixth repeater 16 is a network e vcomposed .of two tuned circuits e, and e2 each designedto be resonant at one of the minima of the curve "6".. to give an overallv .characteristic as shown by the curve b, of

. a secon 2 which is substantially independent of frequenc At the left of Fig. 3 is shown correcting network e associated with the ,preceding, group of 'repeater sections. Obviously instead of using .tuned circuit other types of well known correcting networks may be` employed iii place thereof.

This invention is not limited to the particular embodiment shown'ibut may be variously modified; for example, as described generally above. Similar arrangements may also .be used for correcting for phase distor-` tion or for both phase distortion and attenuation.

lVhat is claimed is: 1. A transmission system comprising a line of a plurality of groups of sections, at-.

tenuation 'correctingmeansassociated with each of a group of sections to give each of said sections similar transmission characteristics approximately independent of frequency and means associated with each group of sections Ito substantially compensate for the net variation Pof the total transmis?v sion characteristic of said group of sectionsl from the desired constant,frequency-transmission characteristic. l 'A 2. A transmission system comprising a multiplicity of tandem sections with amplifying repeaters connectedlbetween successive sections, means as sociatedwith certain repeaters at points along'tlie system for correcting for unequal attenuation of dii'erent frequency components ,transmitted by the system, and means associated with repeaters at points respectively intermediate said eerthe net attenuation of,`said systemincluding the other repeatersA and'their associated'correcting-means, whereby substantially complete correction is` madel at a number of' line a pluralityv'of sections apart, correcting for the net distortion lresulting after the first-mentioned correcting steps.

In'witness whereof, I hereunto subscribe my name this-28th day of April, A. D., 1926 BRUNO .`G.' POHLMANN.

tain repeaters proportioned with respect to 30 l

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