BSTJ 50: 2. February 1971: The Picturephone System: Baseband Video Transmission on Loops and Short-Haul Trunks. (Brown, J.M.)

15.6 MB·English

‘The Picturephono’ System:

Baseband Video Transmission on Loops
and Short-Haul Trunks

By J. M. BROWN
(uses sscvadSeptembet 25, 120)

Local Pietarephons® staie teil be provided using presmt tephone
cate Joris, lvoe eile para are soqived fr ack Pieturephone call
fone fr audio and ts Jr vide troneniasion. Underground cables wil be
ed exontly ad arial fociten (oo Ke emt. cable opuior
Sot prowile sia gaint compeneat for ele Des from 5 He to 1 Aa.
Thi aril dvovane the plan for providing Bosch ride trnencion
‘on poive ene faite, the cable equalizer ais fate, the fnportont
rates for engineering the widen trenamission ete, ed Ue mainlovencs
iontur

For Plssurephone earvion, buscar video sgnala are being tvens-
rite on entaresloope and shor-Tul iieroice trunk long zoutes
Snir Uo the onae used or preset elepaone serves. te esonamiealy
Atiraotve to use ordinary pms of wires jn Uh iting exbla for deo
‘ransmibson, One pair i aed foreach dicotion of ¥en trsnanision
in addition (othe psi ued forthe aud signal

‘The base wensent needed to priv villo transmission is « axble
coqalier, whieh provides taped yain la rempensae for exble Toe.
Prosat davigns whieh aze the subiest of tie paper are intended pei
sarily for undergrov! 22,24, and 26-gange paper pulp-insoated
tonduetors, Uaderzrond calle are preferred ines they are eubject
to lese temperatare variation and interference then rial exble,
Toture eymems now bing designed wl have temperature regulation
fad igher trexamision levels, perailing the use of longer wnder-
‘round loops and trunks én the use of sevalfaalitee
890 runs wea sxsrese tmoMIeAL JUUEAL, HEANUARY aL

‘The typionl Insubund video transmission eywram of Fig. 1 shows
‘to Pictaraphonesttion sce intreonseeted by means of Piturephons
Joop and trunk failtios and two video evitching ofices. Te audio
portion of tho Pictrepione wytim is uot shown nor sewed inthis
paper. Fixed sheped gain coble equalizers, desigosted with an "Fin
Tig. 1, are sod inthe outenig divetion of trauamission from evitch-
ing ofiece to equalize for tae carefully controlled offee eabling and
switching loc Adjustable shaped gain cable equalizers, designated
ith on “arrow” in Fig, 1, compensate fos wide range of cable Toren
‘Tho enblo equaliser astocated with the station ect is mounted within
‘he sation et servo nie we discussed im Ref.

‘Tho vilen switching offee traneniesion plan is shown in greater
otal in Fig. 2 "Tha video loop and trunk paire are browghl ino the
tice through the main dietbuting frame (MDI) wo the incoming
tnd oxigoing sable equalizers and thea to the wideband ditsibating
fan (WEDE) which ia uavd for eviteh load balancing popes
While loope ccnnest vo bota the karzontal (I) and vertical (¥) eon
aneacions on the SIDF in ordr ta provide fexblity, trunks conneat 10

ea ced I nie
Tig. 2-Fideo eiching oer aaninn in

only the vartials on the MDP sines trunk rarmangements are not
aormally Tequived. ‘The cable Jmgth from the centzal ofice cable
‘eqalizets (COCH) to the WADY 9 aletznaly tule out 350 ok 80
fret of 24 ngs nhling hy mcane f the Blok Inholod CBO}. ‘The lor
(tansmission path from the WEDE through the shreestogs video
soritehing mets tothe crunk ect i eareullysontoled to 160 se 40
feet Likewice the trunk cabling from the WBDF to the trunk cccit is
nko eareally oontroled to 16U = 10 fest, Consequently, the traee
‘mission lee om th inotring lop eabie equalizers through the central
ofc to tho outgoing loop or trunk cable equalizers ia equivalent to
tho sum of {3801 100} 180 + 380) cx 1020 fst of eabling, ‘This
‘contra ofce transmission Ios is eoraprasstad by the Sued choped gain
butgoing contra ofice eable oqualizer designated with an “>”, The
Video aniehing ffi bi dinese mre detail Ref. 2

‘Other situations, shown in Bip. 3, which requlte the use af cable
squalene include video Uraesisou Uhsough easier ele eoieh=
Ing equipmest, mach ax Wideband Remnte Switshes (WORS) * Key
Telephone Systems (KTS) or Private Branch Rarkanges (PHX)«
For video Ince Irom sero Wo wpprusmlely 400 Jee of Bswaugeeable
htcen the station set wa the KIS, passive elation ach Dil out
rnbworks (BO) ace used insteud of cable oqulizrs in order to build
but chess nes fo & Fred aucune oF buped lee. For the dizction of
transmission from the sialon sat toward dhe RTS, hs loos
ousted by the KTS ci equates on Ue centred ole se of the

sansa HoH MKesERIOS m0

ICTS designated F,. The KTS rae equate on thy ete fie sie
of tho ETS davguatel will wa arom providoe Bue pre-enlenion
foe this bait ont TS line 1s for aabemiasien from the RTS co tae
eution set ag well ap adjneablo equalisation for the preaeding loop
cable tection, For station rnin lnyune Le re of Ui sain
buikiout networks, x suation se: eabeequalicr and an addicena: KTS
cable ustizer ae syquite w sown it Pig.

‘A cuble oquuliscr is required on all video loops and trunks coming
Into a PIX Since PRX enitehing and Learaintion Jos ia aigible,
to euble equaitra are zequin a ontaning ‘oops aid trina

"A.WBRS may alsa be not bereeen the viden switching offer and

Pictrephone tation ee. 4 WHRS is an axteion ofthe video
‘vitehing foe end under fea dest contol but remotely Ioeted om
the oumerert promiges or ia another snitehing fice not eyed
for video enitshing, Thin uel ta roduve video triemieson oct by
concentrating a nursber of Ips into loser mmber of tule con
nected to the eoatcolling vidao switching afte, ‘The video ‘ranemigion
lan far u WHS in essentially the aame as fora PBX.

1 eumomer'seerving ceutal alte [ur lnlepuve gccvicn samy not be
Uv game cf used for evitching hin video salle, nartionlory im the
carly years of Pcturcphone service. ‘These serving cents firs Way

cin intermediate sable ecvatinen (ICTS) or WHMSy which ace
sed for the vilen pott'an of a Piturephowe en, The iniiy whieh
Inlortonnrala ts serving sonra ufo wilh the video eniceing oer
fn engines ta vidro tine andar” ino comer sir to cet
towil for baweband video turks iatereounceting two vicea ewicehing
foe. Suck planning eliowe a wracfal growth eater; carving entra!
lla vido exsigenent my tmogreas from ICH to WRB, aa Wen
ltimately the afice woxy Beebe 4 veo eviteking oes ial

Toop Iranrvineion Tlves ue used we interconnects. PBX or
WRN on & snnamer’s premiece with a video omiehing ole aud re
called wrinks,elUboagt Uy are epineezed? a8 loop. All ether tran
sisson fvelitice not uleudy spoeitcally daursed (se Fig. 8) ure
tegineerd ne leap felties, Derala of tbe engineering ofthe loup nd
trunk ideo transmission system aco diseuszed in Seeon WT

earn nA Me BEN oBFECESE

‘The aahle sualiser wor desirod to eomapenstte prizeatily Jor she
Ja of 2, 2k and Abzange limulaed cable pais, or mixin
there, The muximum esble equaliser gain was limited to 34 AB xt
$000 nie nia suArT THRMNCAR COLA RECARE HL

1M, The esieron which waa ueed to delermine this maximum
‘Wlowuble equalizer xin wer Uoee tae nour-end orostale Joa of the
able should bo greater han cable equilzer gain Ty 14 €B for 298
pemment of the ingtlcocy, Consecnersdy, the equalised exble section
Tength i fimited to approxicnely 8 ilofect (Lit) of 8-gange cable
fand 8 Sit of 22-enuge cube, ‘This Tiron abla auction Tonga ia
geass more eompletely in Section 63,
"The mene” of cable aections thaw my be wuseade? vo form one on
ia, in prutice, Fmitedépfoema one fo fr seston duc to the aes v
‘Shangingeableomertion Jae eased lr casing ambient tersperatares
In ower to detamine idividval ese tection deciga objectives mith
8 tle and rvadom noe porormance? fram the leap objectives i yas
Iman’ thet a mszimun vf ‘our table sections eotapice a Toop.
Powering eapabiltca and maincesuooe Seales ere alo planned on
‘his baa
‘The valixti abjactiva was to compensate for the insertion lost
of able esetion to wc -£0.1 aM fin estetisiy do to 200 XII,
‘with the limita iereoing to 0.9 UR ab 1 Ma, The amplitude re
sponse atthe lowe frquenoy ond ofthe band ia datomined by tho loop
{it objenira* The tit obleetive canols the amount by which a do
ignal may chacge over wivoninlarsal of ttoe when posto through
‘sb ao couplad fealty. This mjuineoens controls the allavod elango i
righ of one Worinontal sean Ting esused by cho Pisturephows
ftanmuzson syctom ite, Fur m lnnp tt ebjective of 1.5 parccat
per 100 ye and Zowesction Tnop with fre cable equaicr, cua exc
‘sqalingr must aulty it ruirament oF 03 pero. We wasn
Unt only ono RO ln frequaney coupling network i dominant. This
tasunpeion equires on RC tie conan oat Tat 38 gor 9 ase
tamales fvquneyseaponae which is 3 dB down au 48 Ha
"The sinsuidal vignarhandling objective fot the oable equalizers
vas ac at nominal O75 V pee over the 1-MFiz tmqueney band
trl n GJ margin againet evenond, The @-dR margin love for
‘yslem oniliguinent and for changing cable insertion loss due to
hanging ambient tamperaciro, The eile oquatizer gain stability ob-
Jeeta for a 40°F to —HO"F tenperatune exvironment was act ab
2202 dll ob 1 KHs ond £03 dB st 1 MH. ‘The eablo equaivor wore
tbo rogired lo withstand Wighenng ranges which ar Exited to A00
Dy ear Mock grolelors
‘The presetoe of ‘knee longitudinal signals on video pris, prin~
‘pally 0-H signals, may ovev'nad the cable equaliser inpub colworc
ever dius worl ly gmarate Bie ale equalize
‘ama rom masssemon am

powering voltage. The eable equaliser was required to tolenie a
TO-maA pea: longihudina vureat and seven a longitudinal impodance
of 100 chs at the input (equivalent to 1-¥ pea et the opal) and
BF ohms ab the aulpat afm lovally powered enble mmnsizr. "The care
responding mximom open creat Jonsitudinal pir volage thet can
be talerno ie npprosinately 2-V pork por ile for 25-gnige exble
and 1-¥ nde por mile Zor 22-pyege exble, Tor the unfergeound
ites that aro eomtomplated for the curly vous of Piturephone
rerviee i¢ is unlke'y Ua longanoal sgl wl exeed thie level,

‘The weighed eam noise objeelive’ is 65 ABV across a 100-
om ferminetion ub the eystem sero Pictaephone trunsasun level
point (0 PILE) Jor w loop. ‘This moive abjewive ineludes cable
equalizer noise end random interfezence from other aysteris eoupled
by means of eable fnstaleparhe. Tae noise object per loop duc
ta ony cable equalizers war ce, at —80 €BY, slowing 15-88 margin
fr noice from ofbe> sores. Assuring feut equalized cable sections
per Toop, Le weighted noise ahective per eabla equalizer bosoms

{36 dBY. Combining te weigated nsce characteristic’ with the cablo
squalirer gein cheretteristc yields © freqieney respante mich 12 2D,
ff gcin which is 3.dB down at 48 Hz and 600 kis. ‘The thooeetical
oie performance of aa ideal noieless cable ecualzer with this indi-
cate weighted ‘roquenry saararcerstc is ~114 €BV. Ilene, the cable
fenua ir soiee guns objeative ia 38 dl.

"The longitucinal baltoee (common made sejestion) of the exble
equa er inpit network! shoud be voinewbat better chan te lone
{aGinal baldnee obiinod irom paired sable Tuilisies 20 thee cable
fueiity portosmenee is hig. A longtadinal stv one
pair in @ ezble may be cmpled Co a Pisturenhone pair ‘rough the
Tongitdinal-tovongitudinel near-etsl orosstale path (wih Tost Zac}
int Then convertad to en unmentad tranreere gna! heomive of the
finite balance of the ina! network. ven iT Ue int aebork bales
‘wire infinite, aa uxanied ‘rane
throug che lon
love Tae) of the eae tel. Corset To input newer bslanee
BAL.) ie given by equalion (1); m 10-dB mungin bes becn i=
ted to dasuxe that cable balance fe eoncroling ast 95 peroent
ofthe ime.

BAL ~ Ley ~ Loe + 104. wo

‘ai per, ASV le define 2 wth tapes fo 1. ro
‘Hoge acme) Traovene Cals) © nated! Cai 48),
402 onus svorear rocmsteaL JOURNAL, MEBROABN Mt

quation (1) wae ured to determine tbe ingut nctwork balance
‘objective froin 90 Kile to 1 BBs wo ix shown aa part of Fig. 4

‘For the Treqieney range from U0 Ha Wo 80 KH, tho single fe-
qucary interferonce (SFI) requirennet! of ~65 TRV et aystem OPTLP
{yas uso Wo delarsine the ioput network balance objective, If the
maximum looeivilial signal (LS) preset at Ube inp of the cable
quali is 10 dBY* and the mavienrm ocble equslizar goin Gis
YO dB for the 600 KH to 30 Ks frequency range, then the input
‘ebwork Uabsnced should bo Of dls ee given by eauaion (2)

BAL, = 18-8 + @

For the low drequeney rane from 80 Hx to 600 Hs, tho input et
‘work balaue ekould be mich thor © 60H longitudinal signal wt
Uy BY, the mexiavint tolersble ‘ongitadinal signal, shoulé result jn
4 tranerere signal 20 grealer han the ~ 8 BV power bum re-
qrament? for a ln falling. Asmming u exblo equalize low fre
(quency gxin of 10a, che inpae network baluuoe at 60 Ho should
fo A aD. The oorwusite halanee abjctire dor the Snpus network i
shown in Hig. 4

“The balance objective for the balanced outpue notmork af the exe
equalizer ie important Wo prevent canpling of &vidco eignal from one
ideo pr co rnether or ta avatar ye of tenamision syotem. Any
“unbalanee of che ouipu network alle transverse signs's to be com
‘verted vo Tongitiaal Wgnala and
the longa
Even {2 Whe out network baleaee were induite, « tranrvorse
fignel ax one prit would eaves a traverse signal on snothar pair
“ie the traneoran-to-traneveee nzer-anderoetale path with Is Lae.
Consequently Cie halener of the oucput nctwork theuld be grester
than Lye — Top ploe a 10-cR rrargn, relting in a 20AB balance
objective forthe output networks for most ofthe foeqneney band of
interet

utp network balance objestives more stringent than the 20-38
balanee eeaaeed above are roquindl for tmovcly powered Sater:
“ecine eable equalizers which re fonting with rapes to earth
‘ound. The feedoac path around a floating eublo equalizer, shown
in Fig. 6, 16 one of two posible fcodbacc paths whien involves the

Tg olin docs fn a ster ote
SLs Hekate aera
swazaaso vinwo saan 02

—

{5 1 Top sown lane biti

blanca of input end wutpet nelwrks ace she Tongitinnl tne
Inupecuace wkieh ie veferenord to earth ground, Aualsa of these 0
feadback paths yeh exntally Uhe ant buliee requirements for
‘he antpxt netwn-e; Tee, only Use siaatien sbowa in Hig. 6 wll
edie Bere

encase of the daike balance of the output network, © transverse
igual al the ouble couelice ouput is converted to a langitodine!
‘pnal ich loew BATg une oovplal to the ioput of the cable
quali Unruuch she iougitudioa)exble impectnoe at che ‘mpc snd
woulous of cho auble equalies, This legitadine! goal ia then con=
verte « Usverse sha by Use cubalenes of the input network
wil an addifnad Tos BAD. ard thea simple by up ta ti a,
dhe snort ene equalieer gin at 13s, Consequenty, BAL we =
BAT should lve sigoiiantly router iw 64 ol at MEE, TF the
Sap network balance i 0c al 1 IH, thea the ouput netrore
belanos should be much gestern 3 — 60 e 4 dB. The output net-
‘work balumuo requirement we checeo 8 AP aver Tip I-Mka band
OF interes priwerily because this arnoont. of alanee je ral
Achievnble, ne indicted in the neat eeoion, oad provides arnle
teemuaion #0 suppress the wrwanted Twat,

ho cable oqualizer consists basically of au iapus networks a static
equalizer, xad ap output network as chown in Fig 6.
404 cous umm eveomag nauansoat 2ommUAL, FIBECAY HL

ne eh send «sings prone he ee th ae

‘The inp: network ie high iin dicential coupler whit
sovvrestn de inonting belwzted vignal wo tbe unbalanced erode fe
fqusssetion, This networc iv eaymeitivaly eouped tu the exblo and
twits a xed conser sapped 100m resistive termination to the
tal Thie {eae teaination wae coe becacss the chemist
impedance of pulp ears paite is apprarimscely 100 clu alnve
Top kite. It is this coupling wetronk which primarily dexrainee (he
ABs SAU) comer feequaucy of the eoble oquainen. A fat gain

i. (be evaes