BSTJ 30: 1. January 1951: The Evolution of Inductive Loading for Bell System Telephone Facilities. (Shaw, Thomas)

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‘The Evoldtion of Inductive Loading for Bell System
Telephone Facilitios

SES sh stro te enters ductive aig ihe aot
‘ithe Bel Telsphone sexier ui eset quent ste. Ta particne
a,c how thea ron utbos ve heen vide, We ate i it the ze
conan vale of gata search, of erent siete nd sgn end
ionomers ninety of recon 1 tear, al the
boon aoe erancring prizeipes tothe design ote ire ph
The sory sac here i lor eniely cancer with series indussace
il bing sine eter =yps of linge Fal vy Hse use i he Be
System, To nake the sory mone complete, hover, be” acuunt i
inclaced of BL Sysiem developments wd spliatoes uf coutinuots lade
Tae min sory tars on alee Ge tara af the cerzary, slowing the
dtvalagment of Ue Hist saedand. losing ue aed wins sper a
vie Pragh ta Fe eu of IMD, Kae beta of tre orbit
tr shee on nnostly netted igetsaee sa the ringe of eephone eas
Ison over open wir ings and exbls, ai in thet of ebraper cae
Tn ta coection snd be aeenbered that a really tact te
150 nay anus gvgrme moaancan ous, aNuAeY 1981

Df tlihons vepeater dd net become ave far gene use wal 1918,
hous 15 yea aftr the fnvetion of oui

he camera tia the wwii wie of rading to extend the
‘arcmin range of sponcrize nes seas reached ia 191 several yoste
efor the yacuuticcube repeater ome real. "Ten, repestes and
Voting had bn la Weed a teammates 10 roner the transcontinental
dliconces, Suber’ nprovecent repeser, aus equpment aad
Cris evetually mde evans a dtinue open ze loding

simultaneously opened 29 impr ew ld for npodancesa hi
Twang the entrance and intermediate eles shat unaveide arcu
fpotetie lies, Wen Lane Aspe of cartier epee herrea able
Ee opel fh, several ne typee of “oyeaner malchirg lain
fice for thee arr satu ere evloped

“Tey lors tn ectend se evcetniesion ra: piste cables
fn compelton wilh pesvmise He, =9 a8 to alin ners lailisy of
sevice «vl lover Saily cute ened» rim dering the peti 1811
Tots inthe ase of compost, sal My ed 13g al, ad of ode
Frye any as loge ag the yen Wn henge, Thip Uead slowed
doa sully fee vaevortohe repeatanebeeass tomers ly wx
‘During the net floes pearson etesive Geve-opmens werk or irre
epeners on eqlsing il sjulatiag aos, sd or higher vel:
Tigher eit Fling rade Seale to ost ISegunge roles aid
Ioacing cos -w hirpt has :Te iil standard cle et for ines
aogig tp to whoo 1500 wes.

Th the exchenge arse eable plant, i esting bas male i ease at a
le ont bnsnent the weeds aepors! hy geographic “elena th a8 et
‘pry Hille onapsitiae by elpprone spears. Large reductions ia the
(ete ofthe aa pact bro nein! Gn the eseaeive etition of 27

tal pee cables. ade se hy lhe ws nespesive lading. "The
ful-lrally conte tsrenielon developments io exchange urs. =r
fees aleo made pec inpurlan. inpooveteats in the intel isi-y of
aration Ey sng Wher rut loading to transit wider speech
Frequency boxes

“The imcorent esting appanacas develspments fn che pad evel
by she roview bee ake Call advantage ofthe development a. fy even
pec ‘reals of & ates af enone Ieee ayes acesaate’s
Time the tisueoiesion sere'ce vere ance ur retuce leading cost
“rnin mb tee feats. Te lang ei onteednaters which
ese irom Ue ge soos ina wale psi by “he standarciat on
Sh vomyrnese! penal pomder core lounges ing the ate 192
‘were eel rst a flening the growth ofthe og tance ad
[BLCTIVE LANG AOR neuHONONE wReTERS 131

retange ero ele po, aed in leg Ut iportant sec improve.

‘As descsbed, step by step, in the preset story, ol Iwlng has Been a
seep important flor in miking pale the psn of satsfoctory
Ista eesie sf regonal se whieh nvr arcrags a conte
‘Eezeasiag tae, Inportant elements fa che plc saiactioy ta shich
‘ling bas wee fusaeual sontibutinns aac: (2) Higa qo tan
missions 2
Tenge scoops of selaively lowe! faiies. Iv the tensive ution af
the longisnce sevice war lepeatesed, hades, voie-frequeacy vl cxble
fucites, loading rast ofcourse shore he eri fe the inproved tans
mission, plant evet-adaction, and spel of service with the telephone
Fepeatets and associated equalising aml regsating etwas, whet ine
valved

AUT the el aang devlopent work fr Bell System needs intating
he aeciedevelpsments dew in the pseu reves hae wn ne
by Sel System perp withoat oul ail. Coil eeding nas independently
invested by De. GA. Campbel of the heedqueriene sta of the Aseria
el) "Teepaoe Company, and Ty Professor MT. Pupic? of Columbia
Teri, a: nery Lie ame timo, i 199 The patent ntrference pro
Cecdinse mace noveneny ry she cmficting ai of he Popa ene Ca
bet agolratns sud is a prkwity anaed to Pepin ding Ace 190%,
tn he ais «ew days cele cige cere. The pomp percha of Papi's
Fights in the invention heirs Ue interes atin Lad gone ae amir
‘he Telephone Company complete from tse thee alin
ia the moss sdvsatagoons ny

‘Pe inproverentsworkal wut and aplied ws Che yes ae principl
the to ron setts and enginects working as teams on varios pases
of the triemision research, development, aud engineering prblersi on
Tw magnetic materials rseuch and devslopme problems on che ap
seueresigh avd reansactoring problemas nd oa the Geld constuction
tnt Sale pens, Neil all aspects of telpone eysterslevelapmaent
fave been inves vo eas few exe

Tr abe ogress, a lage nutes of eviuale hove rae iment
conlebutine ta tae advanverent of ohe lene ar. The welts T's
Tevow igre be segue’ as = spokes jah cn work, Since “Ee 8s
‘men of air aur of psn era ech vidual bo a en
indeed won be exten discal, ei aot atemptel tbe present

high spel serve fitted Ly the urvsion of lta
152 me aon ststi9e emma oman, ARE ISL

PAR I: THE BEGINNINGS OF COTE LOADING

Coronas Taons

or present varmoes, gaoueprsenation 9 the matbematial Lary
oi ding ie caneceseery, A simple eserigLow aul a bef satereat
they is fice,

The priaaty pupor of cx Taadng i to fmprowe che tana af
inulipence ny absent yl ing e ueult atezeator, are by waking
the csv attsrcation approvivalely vif shrougacut a predetermined
frequency bal These traremvvi eral azo ebtaiaé by cvialyin-
‘ring els hing norm fens ase values oyu securing ite
Sal alog the exci, nae sited ra equeney- ban bel the ling
tall sequen. Tri i an ier fonction of the epare ool of the
prods of te oi inluctacs an of te mats expire he alg
Ecctons belnees suave eile, 96 determined by the eal pacing ane
Tintlengthcapactaase of the cen. Aue te loading cut frequen.
there ie suntantal suppetdon of isin

Tor mae tht a docade prior to Cansbell's and Popins 18 ass,
thy thearetialpossbiy improving sanaission over clepkore Few
by anclly inerasing their feevawce had Deeame knows om she
rotheratha’ tude of Vaerhy sad Heaviiee. lo tote hoe been com
erable soesulator ye head Ly others, egading te pact aby
tl aporosimting the whew daa of calf distinc indeence by
inserting lov-reslanee indtarer villi the line, Rules for spacing,
{helaredfalussnces bad not been ork! oul hone, aoe hed tale
ceil ben deve

‘he rel ce-pacing tame oat to be sch thet there are sewers
coils or eave length at the his! feutisty whic stow be fice y
tensed tu bin sister deteigQilty. Here, “several” res
note than tvo, since at the Unmwtial cute frequengy thee 2 ton
foil pe wave length, era of the nominal velocity of prope tion of
the “enreapouding smooth line” Gv hypothetical Ine having the me
total indetence rd conastaice) thee ate cols per wave eth at the
fated frequency; rxpresaal in "ide per second” Ths namin yelacty
iseactly fines the cut feqveney fm eyes per second.

“Thet tenotin:irovement obs nable with lading cozespends come.
shat tothe incase in npedance Ua ress fon the creas in induc

eves nics ns eet hey re tng
apa are me ya
BESISDERes Cee Goes a gle ee
SUP SUMRME hde S autdctes a neg
Iuuerive LOADING Ye MELTS waenLTES ss

ance This can be unveil fous the fat that in the taw-eapedance)
honloaded creviythecesey dann hese whi ate proportional 9
he sane of the lise eugene ste onSiaiy very large rater to te A
tlseinedsigtion Ge sont loses whith are proportion tothe can
tthe tine tenia Won the line mpeanee ie inereased a saitble amoust
by che loading the decree in srs Iss nicl eater han he intense
i shut sees. Ip conimercn|pravtee, ennomic tert generally
own ie oe of high aig impedances waieh woud cel in the sunt
Tees hac 38 greet of anecce La the is lees

Tn svualanm nla vee Sequence actexation poverrent she
rine’ pal etic, the uss teanmaen ns ean usa ye reed to the
da i ae tai to teoureh nf fn ronal wie. he eluction
ae tha this ot low vole fpenres sd ne at Hh Eguchi,
‘sling ina anic rote cosform transmission af the important frequencies
at are rogue fr snugly ae waturaluess. Ta certain situations
Tehich wil be ezcuned Inter ler rai af senuaton, reduction is ac
eps! iv erder to otaia other, mone impurans, Uansmesion advantages

Prosesnase Devazerwescs

‘A fell awwuat uf ti plonerig etarch and development stork woud
Anke och tive space Hf ale Law seview devated pia 7
the evolion of the lag set. The pteseat accout i tetlore ‘ie
tora viet rserptnn of the et ltaing patna appro ess
that slid io the pnceing ke

‘though the sino ef the 189) laboratory Savetgntions, ancl the Ball
System's Hen spesinestal inetalations et ecebangeenbles a on pen
Wire Tins, suily ull up a sbstenia dems oe ling, Uhe ee
Fen‘ ayydisatine bad to be delered pending the development of

SEcifrctony yrs of ang cs) Thea ese flowed a serie of wha
Sool te vier 9 Wal Installasons ot diferent pes of long
telored to Ure apuiic nsede of patina pron Aralaee of the er
Torn humors cf chose festallaions, sopplemen:e by coating

‘xperimentl work in be lraony and by engneesig cate tai, re
sulted i te etasishrient ofa ans of etzndard ssl oun ys or
fener ln fy Dt. The commuetial development of satsactory open
tire lng enrvonter any even more corsphcred problems than
howe inrived ia cable loading, atl in commjance Lie standard leading
le 10Ea nes not vol all 1N5. Tas sara type of loading be

ounces Taio twos

Ihc ari sien ip iseany Reecee
ace i eeesome Sebel Compt ar
154 ioe net ve rRcmICAL JOURNAE, JANUARY ISL

came stance fr 16Enil fine ny 1910, afer @ long pti! of wena
lve weno got beter Freinltion

AGT ths ealy leading deveimcat work was for non-quMded cables
ae fur aospltomed apen-vie Ta.

ang Colts

‘Tre eacliatapocuasion anpeesins reguing eo

eg, rege

Iu vita! nee for blaiing 2 he tio of el vn Ua eu 1
sistares ead by npliention «hrs tn feo esstane to coi inductee,
Aoinat expect thie ore et to be ict desig a me sulscturing
Problem, repel Sih eon “ning with was give dovelopmioct
prorty

iy Api 1H, a wey stlstory cote had bees worked ot or
oper-viteloling hy Me. II, , Werte a avendate of De GA Campbel
Teal torte coe, Reed by minding a Dune of suite i a
sve, tle in mee, an 9 sity ped spool, sever es of wire
Ting sl each eae, The manvfactaring procs of the oateds supplier

= fre. ceeee fF.
i

inde cod deaning to obtain moptily ard wee having nit
ete of thoes 66 "het Borenindiags, each cade to eat
Flea ofthe core wing ce de use of uate, eens wie. Tae
Fine svn nf the magi mater oof he copper conductor Was
fssenil to te satsacony conte of ely comet late,

Those Cale No, 3, was the Lest atacand lading es rena
sane! for about a oc tia redsige bcame neeessiry Wo Fiat
tv esitsive conta exleitatinof lastom working, ecanse of ie
{ery ler ceian objective, I bad t Boa lenge cui Some ois
{lnensona and lets! escorts ave indo in ‘Teble T. Tw sey
Sivas epprosimately 25% larper tha Uh lyst eal stow ir the heade
piece

The cable lading vile Het in the table werrstadized for gener
vor dung 1904, fllowing vseaiona see of other Lypee uf culls heving
Cieret inductances and ia come instance sng. a dillerens care rater
‘These rit were generally sins in ther base dia Tetures othe oper
vite loading ey but for evil reagons wee mace llr sis
‘Novenive uaanise oR RELERROE sce ass

Ao their ratios of eesiance ta industauce were conederahy higher. Ta
Sn these cil ve typed by Col Bin the eadpec.

The tl (Wo. 88 AWG) wi use in ew cable ol cores ad a
rorina nil permeability of 9S, nealy SV, Higher than that of the
‘pensive eng eo corse, ilerenes iy magnetic forme
Gn ehtorterihis, octal permexbil, cre loses, ant certain oer
featuree ssiaequently era, relied sey fom serene in the
sealing rel ring the winesraninn pn

‘dia print lfesencee hebneen Ue cle el aud Uae ap.
wir eit wore (1 tho tee of nomstndt conductors in the wizéinge of
{he cable eal, and (2) the use of lower diclectrcsteengh Salton in
"he ele eis

alae ay | ae rile |g |
RP RE | fa | Ba i |e
a fie | ocd | aa " a | a

nating Ce! Cosee

we nevi lau cis ce fdivdully poten east ion cases
Vine or raeuting ple Rtas. The cil xanal sued (on he
‘te in inva) rabber-nslae lea

"The cle lacing co's were assembled in lai gromps om ern
spindles, and pote in cat ron save allale for instalation im cable
enflee snd an pole fii Uneral eect eax ema (1) by
Inounting adiacent cle xo there wold Ie appetite rime
cuplig between thee (emll) magnetic leskage Pls (2) by sing iron
hieingsensers ein adjacent cy al (8) iy plea the ape
one of wil in lca comarasets cat in the vases. The cae
ferminal Ils femal Togs the eats in wisely Iersoverd sl
‘able

rir to potting, ce ells were toroughly dred out ander vacuum, end
were negated ith nistreprosing compos

aading Systems
‘As pueviaualy cnt the standard practices Sor eae loading eee
etabsed in ésarce of thew fr apenenne lings biel
136 rum ree asian avin, rosmaa, TANCARY 1951

caster cereal hegining. The #finest. cable lading wanda
wane lite, to prvile fr ange of ater redution meron,
Some tn sanding these syserms acs got Table TE. The tansmstion
fate apply to the ealysypesnrale having en average ral rapacitance
ff show O70 a

‘The ticwetical leading ent? Hequsasie were approsimstey 2300,
cee (about 700 lots pet accond). Tis rt landatd was the esl
‘Tentenve serene spec tonemsion tests tn deterse the inimrs
tl frequency Hist would be commercially satifaccory with reset
inteligibiy. A materi Biger est wd Lave increased the Inaling
oss by rpg the aug si ta be roe easly spaced

“The ter ecananl esse lone sed No. SOL col a about Site
spacing, sving sm pase of abot 2100 same an eut-at Frequency
tlie tothe sana aut feqnency for able leading. Under dsr her
sulstion combi (3 megtim mies wr best) the attenuason oss
Sn he 101 mit nd 16a sags were abou: OOS nod AME si
fective. Te cosespending news without Loading were 00 ard O08
bj, repertively. Tae appeosimate Remilespecing ated nih the
pen wire Lanapuition gargersets ne gave w lla aitenuatios
Ie reduction, The rere lems to secure much praterattenuacion
‘luetign nd involved toric spacings, ranging dows to 25 niles, ant
‘tere unaucesfe, At exteed pero of lw line insulation cause Dy we
Cretther thee higherinrate lnading arongemests bad poor tran
‘rosin, snetiaes wor han muradod ines Barve ais, costal
Sd lloras aloe were ualevarab noe
wus oniNe wow tow anexTUs 18

Penwrw or Seassgmexr Devecoris
General Onine

Vor conveniena: in discnson and ease funerary It ha been
fxn deceslet dividle the rrsinng suet males of ts ei fy
coral pars, each covering a parbaular shase of Uke evelurian af the
“lng 2,23 allows

‘Pars TT- Taig at Leng Distance cut

Long for Exchange Are Codie.
TV Calle Loading Col Cases
‘VL fa Tnideatal Cables ix Opot-Wiee Line
YI-Contimioes Leading
YI! Extent of Use ant Eronamie Signe,
VIT—Summary wl Conan
aris Hf, 1, IV, ¥, and VIE are wholly sonsseued with clouding

Ta Paste I, Land V, seve eo lotng rst end loeing appre
developments ate seperately conidere under headings which indiate the
{feveloprentemphasie: In geneva the alsin leelornents areas
inchrancegialeequence sa sto tee srs gether he ftetel el ystems
ent aaasua develypents, Ike eronolgieal procedure also applies ia
Parcs IW and VI The ses which are gon aad he ees eferece for
stint ost, penn Ce ence: tof eee Sxportane developments exo
eet de peter,

‘lil ng tie rie ritclyconceed wil ee evolution of long
snl ilgemiratios to che guowth fe Bll Syste, appeupriaeeforences
‘cafe lauded snguringothgr wintedstvaees tm he telephone art
Stich have infuence the sesign ara performance ofthe long sates

fd apperstus and the extent of se

Leaoking Some

owe rhenges in voiereqneney Taal ysis have en ima
ior the mre of frproving the rine same, freling the ta
ssn of wher irqueaeybands Uy inact dali, The ‘sedi,
‘henge fr teseteced eit eve ested 0 he ann pea prsblene
“kat arie fa consequence of the eet insrewr in revi ens

The landing sper fe eae crus tamil rain beadsatng
Legere anil hoe or sotetroqeaney art acrectraguerey rpc
Teatching i insidemal colon thst near i er ie esa ta their
‘oun indir vequnerente to mee the spite service need.

Loadisg Coit

‘The lading cl development substautaly peal the ating syste
‘evelopment in variety and spe, In mony iotanees, new lading cle
158 num arua svsviae meses, POURNAL, JANUARY 1951

rere developed fo lake advantage of the svaaliity of (aew) superior
Tate, improved eign serviqus, ond fSbrestion waht, for vi
foluetion or vic nyprovemed. Thoth important stances, aew (es
OF lontng cil were nxesagy 7 ptovide for new typos of Tacies; for
nimple, {1} fo permit che cemmertil explitasion of phntor nk
(2) wea networe of coormegunge logetistaee cables, (3) for Talities

Seats 36 RE Here] fos
spent fe ua fio an

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pate ine

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to srenst programs o> nal wedeaetng atone and or neta
Cable in pense curiae

Certain econoie nen hare demi’ the diz we ox the in
vid onlng c= Tote cstedastoy eeton of the review, the general
ee for hang ie ang eo eisnner ow relative to tha f the cit
Fesstance was mrtioned. Ta applying this design wl the pale of
Crabequlirnm™ hs isa & Bee nterion, Ht has weslted iv the de

Tei be wipe fr caus beings wily hee ie fendi