BSTJ 10: 4. October 1931: Application of Printing Telegraph to Long-Wave Radio Circuits. (Bailey, Austin; McCann, T.A.)

10 MB·English

Application of Printing Telegraph to Long-Wave
Radio Cizcuits *

By AUSTIN BAILEY and 7. A, McCANE

suet die rumen at cr
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ee

DRINTING telegraph equipment! lecouse of ite speed, accuracy

ane cavenience in earsaiting ineligence, hae bawome rege
vised as very useful methed of teegraphy on wiee circuits. Tr
some ‘important, therefore, to determine something of the pore
uty of present ype of celetypewiters on rad cites,

Te common practice to transmis she signal fer operating tele
typewriter equipment over wire crete km any one of several electrical
Teas. Asinealiertlegraps acti He ign-e freguenty ang
inte a se iepntan. More recently alternating currents of voice:
Irecuancy sel of higher ecuency have been employed.) Ta employ-
ing rai frequencies for operating eletypevriter equipment where the
onerating ienpules are o longer puided by a wire crea, new prob-
eu ad usy coulis asiae, which are venta pe of ea tee
raph transaieson. Tor this eeasna, ies desirable to veview Drie
the conditions under which sadio telegraph spatcam are operated.

Ta manualesonding sural-roneving practice for radio eegraphy i
tas ten coxermary 10 utile, at the receiving end, only 3 marking
tome or round whieh ie received during intervals corvesponding tothe
time that the seing ley i depresed Tn tranemizting signale from
anvare (rants, signal ofa dilleren fequency is eent out ducing
‘he spacing verods fo order to simplify the keying process, but this
spscing signal in not tlie at the rosiving end. For aural secepion
he nevew'y aul slient resirement ie that the marking tone Be
slistnguishable ieough tie oe. Using eae wecriviog it posse br
‘etinguish the signal uncer a wide variation of conditions because of
the alility of the ear to accomadate itself to variations in cgnal level
ann signal co-noise ratio

in J 4
on BELL SUSIRA TROHNICAL JOURVAK.

From the transaissioa etandyein, tape or automatic sending, it
sending for # tape peterated in accordance with a telegraphis ox,
Rineelya matter of increntig sped and acenesty of the characters
fanamitied.” Automatic tape reordiag of radio signal suc ax by
the sypton resoner ne similar device, ranoves the alvantage obeained
ion te tone craccer of she signal #0 eful in ear reemon, and
tubsttusee for ths tonal character te Te acute ability ofthe eye ta
tletinguish between signals and noive on the tape recore* Tm sacriie-
Sag chs ability to receive with gree accuracy’ ta the preseune a emi
Siderabie noise there, however, a gun in the speed ef receiving lin
Signals. The tant sd which iim pecmanent form, makes it pos
be for several operator simaltseousy to transeribe feet, parcs of
the reecvw! message epeeds mel slower then the ¢ransmicting
speed

Tinting telegraphy goer one step further in removing the human
levee com the process nf rersiving and substituting aecbaniem
Ivhich sane: be imple to a delaite act hy ear exrvent element re-
Caved. The printing schaala inevitaby recirds what it receives
Srilhout using any iuigweat factor inthe proce other than tke me:
‘husieal application uf sus fs tera 62 have been pat into ely
(he desigeer, Uislew the wransmitel signal is received with such fn
Tewsity and charar ter aa tobe te contrlling signal at the receiving en
run will usually senlt, These of pristng talegraph equipment
fadio creuitey therefore, makes “he sgesl-tonoise casio neeeeary fr
the receiving of aatistactory coy greater than would be required for
ines aural reception er tape sigaal recording.

Tt ie of enaserabe interest to compare che approximate sinimu
valucsuf sgna-tornoice ratio reine for satisfactory *(eansastion ot
Intelligence by single se band long-wave radi using the customary
Aiulte sideband carer telegraph, This hasbeen done in thetable on
the flowing page

‘When automatic mwas for recording the signals are applied at the
veiving end of a ruli ecle tis desirable that considerable uni
Teveity exe in the mutput level of the receiving equipmerc. Tiki
ven more important when printing ewipment cused. Such a comic

aE ASL Ma Seely pv mega aw nya
Space tical apart ot ting a
upstate eat tna cos Oconee
APPLICATION OF PRIVTING TRLAGEAPH om

TAMLE £

waves] P| jm
wt en 0 uo 2

wring se Sieg ntl aan mecurements = a of sea 230
(BSc Tolwaboat Sab abve tli: whee sec nat fence

ie ig rather to be expoctad iansmch ae ultimately in the syatem
‘here must be a slay mechani operated by the sigsals, Thi relay
rust with a certain degree of accuracy reprosice the length of the
sgpal impulse. isilesirable to have the relay cemtin unbiased overs
considerable ange of variation in signal level. Ila signal impulses
transmitted only for wacking, the spacing signal Incomes an interval
‘tno current and the restoring force on the relay’ must he snp lo
‘ely Dy either electrical or mechanical means, "Then ith igs of
‘the usual roundel weve shepe ifthe relay operating fooce varies while
the sestoring force remains constant, che sgnale wre either “hea” ne

Tight" that is, ie marking intervale ave either lengthened or shar.
feed add ehe sytem eames biged

‘The most obvioun way of avsiing thes diiculis is some arrange
sent in hich the eeotring force on the relay varied dn a master
similar to the operating force resltng fom the received signa One
‘nethoa of accomplishing this veal which has been fun site efi
tive is the two-tone method of teansmission. As fara te sli cer
isconcemal tnesign's consist of 3 ma:king ancl »pacig signal trate
mitted on stghily diferent frequencies. Since these two signals
traverse che same trinemision nedium, they are at least when there
isn selective fang, subjected «sila variation in the envalent
‘of the tranusion puch. Tkeielore, <4 polar eeceving relay
luprated by using ene of these froquescies to produce the operating
fre wd the ether fequeney to produce the restoring farce so bi
fesults. The increase ii magoiude of variations ot he transmission
o

iret which can be ruleratel hy employing this twortave method of
“raven instead af dhe siagle-tone method ith a Axed bins Ie
shown by Fig.

it I |

“yesiren cunsent (ozciee£ naeve neronence)

Fig, ‘lai ban rl oorect an peinter operat mg fr the
“SSD CONT Gh pnd Se elt fe

“Theee curves show the selasion between eperating cue and the
limits of pee anargn within whieh norrect operation i verre for
tbh the wing Interrupted tone metal of signaling and for the two-
furve method. The upper ond lower limize of te printer aarzin are
Some to meet atthe lnwer sels of received exreent lieating that
the pete tals completely at thew levels. As might be expected, in
Crewing the reesived enrrent level afer dy dos wot affece the orienta
"ios range ae eriounly asa oresponding decree. In each condition,
Towewes the mangin lew sflested when sgaaling by che two-tone
tnethod.” Were it nat forthe presnce of soite an the radio frei, it
‘ould be pase toestaiish the normed operating cucrert atx hier
alae, ‘The reewn why chis ie not feasible = that the elrtors in the
Voice frequenry telegeeph resiving equipment are operatel near the
Upper bert nf their characterises. Unter this condition increasing
the gain cannes selativey eral itereaae in current fom the vectier
thats receiving och nese nl sigal inputs while the curent from the
recifer that is receiving noise orly is increased.

‘Ties because of the desirability of eperatiny troup Nigh ncise
levela on foag-nave ralio crit, it a noe advantages to utilize all
of the available protection spsinst signal level changes. Rather, 2
Cleaponiae ia sought which wil afford stiafaciocy protection against
reasonable signi level vacations without making the rociving eas
font unduly vulnersble to noise. This practical operating pone ha
been seleoted at the zero iaicate on this Fiore, The teranee in
reveive erent Tree variations uml obtained isabout + 3d inthe
‘ee of single tone simaling as compared to about Tb fr two-tone
igual, Or the trnnmat artic longevave radio citeaite warations
frester than theer tolerated Sy che two-tone tranemlzses mull!
Seldom cccur with sulfiient rapidity tv excape mana correction,

‘With the two-tone system the emout afte tering the rect
ing mechanism eames in chrough double the feed wid used in the
singe-tone system" and the intelligeace traneitted is complezely
contained in both thernarking and che spacing igual Tein therefore,
logical to expe: hat there wil not be much dierence between the
(Grown and ssgiecone syetems from the asi interfere stand-
point. TP there were no reveive signal the ire through the marking
fd spasiag Ellen pray woul laner nt to rome extent but dur
ing operation either the mark ox space wigal ie always yrewnt. ‘The
noise my effectively annul eter signal by being apprexinacely of
Sal inensity and epporte phase, bu the ace through the othe
Fieri ersved with the Fill Intensity and, therelove, nay opesate the
relay Fabel,

Empleving princing telagraph equipment on radio reuits fs aot
ew." Thare iss, however, been comparatively tele commercial
tse of such systems and chere have nen very fewr quantitative date
published. Suck peectial informatio ad wpacnitative data ag have
been abvained hy the lll System rogavding tie sppicaion uf pring
Aelepeaph to radi eivuies rebate to longeatance overseas point-te
point communication al a hrtaiatiner point to-poine eveiand cr
uit. Hott of thes crculte were operated on long waves (about 50
Wilocycts,

For the past thice years printing ceeyraph has been employed on
the long-wave rac telephone ceeuit ™batween New Vo and Tandon
tw exchange information pertsining to The apecalina of the telephone
service The printer's admirably suital 1 thin Kind of avian vince
the information exchange frequenty consste of foreign ames of
places ard people a. fanilar 1 the watched apecstors. By the
tw of “he printer, these can be spelled out with speed and accuracy
swithnat the necesity of attested ram uation

"The printing telegraph azcangesnen sve at New Vork for use
sof the (lephone crate department on the transatlantic circuits are
slow in Tig. 2. Tae instruments sor ted on te table in the
foregeound, This table ie lated ane behind the switchboard operae
tors Asa large vonjority of che business tramsacied is of a question
and anaes nature, ‘here are speciat arrangements in the printer lo
ee ‘bene SYSTEM TECHNICAL, sowRNAT,
Snvlicate whether the mesage printed original with tke New York or
with the London serator. Messages tranwnilied feoat the local
machine are typed ie while thoge received fron the distant teem
inal are typed fn black, “This was arcompliched by modifying the
techarisrs of the machine: automatically shife a hall read Dall
black yvina «boa

Phe voicefrajmmitytelegcaph terminal equipment? and ity
ciated appurates re swan Tig. $._ The equipment enmpies the
‘oice-frenuency terminal ext fr repeating beteeen the lec ee printer
Joop cirewit andthe ac fine circu. The printer silching ciruis,
testing urangencats, and moriuoring equipment are, for convesienve,
Jrekuded ia the same sexily of apparaton. The installation includes
fll the suipment necesrary fr one channel of Lwo-tone carcertele-
{graph system and suficiene equipmen: for adding nates by povitng
Sulable fers ul a smi sunt of aediiensl apparatus,

The connection of the printers to the telephone vircait t shown
schematically in Tig, 4. ‘The wananiting Ielegraoh circuits are ot

‘cunnected permanently 10 the io chancel. When its desired to co
taliish the relezrapa circuit, the coaneetion ie mace through tne er
Urs curd reat So che tranetlantie ewo-wire telephone eicult a =
‘nan sia Wo chat wed (amet ilephonesabseribers AUG EC
tos bila, SYSTEM TRORNICAL JOURNAL

‘nitoring arramgenmts ave provided for ee telephone aneentor, the
Technical aperster, and che prtee operator, The distant ésming!
Cperator may incrrupe the printer circle with voice if such intervup
fon seer expen: Tn addition tothe yrinuer used by the printer
Phonon, a prlatcr at the techaieal opera's pesiton, not shown in
ig. 4 i oontiaacusly erected to monitor ua the system.

shen he zoted that ia the arirgement shown ia Diy. 4 two
diferent voice frequencies ar uted for ramvission and two others for
reception, thus giving che mln tages ofthe twu-toae method of rans
Inision, The voisefrequency tenes go out wer wie circuits to the
framonitiag aation at Rocky Point where, by means of ue singe side
Tran suppressed carer matin of cadiowranuaasion ™4ehown in Ti
A they sce changed to radio feequeneieol abou 60 kilocyces and an
ified. The cyrivalent radianed power for cach frequency is abit
Sokilowotte. Farsgaals coming frum England noch the sme process
isfollowed at the British end, the sadiared irequenciey however,
Sierent from thoge trensmieeel inthe opposite dirton

"The must serious handkap fx the use of prinsing telegraph on the
long-wave channel ie noise, Daring the winter months tle trouble is
tperientd, but interruptions are frequene and are acsaionally of
ever hnurs' duration durisg the sunme= meaathe. At ce radio re
Ceiving atatons the directive antenna syste used for tlephony ™
realy reduce the nine received

‘Nnother inportant faclor in reducing reseving interference
freauency eelectvity. The sadio recive itself sestrces the receive
Tene sary to that eit for single side band telephony, passing
Tame! about 4000 cycles wide, This s accomplished by the single sie
and earveeresuprlielrecever* shonin Fig. The band cdmittet
Ineach of the tie cisnel detectors beyond ie reeiver is narrowed
Alo toabout 110 cycles By a wee frequency Bler as ieicte in Fig.
{Tels estimated that ifthe printer Were used continual on the
feng-wave trvatlantic channel forthe entie year, the pet cent of cr
‘ore Would exceed 0 percent lea than 12 per ent of the time and 5.0
Der cen ls thaa 2 por ent nf ue tie

Tr order to obcsia more aoswale quansitative information regu
fag the ele of asse on te transnason of telety penritersigals over
lin ceuity a cevies uf tex was eared une daring 1930, Por the
harp of these fete rao ves was established beeween che tn
ivtng station a Roky Point, Ly Lane a temporary recelving sacon
a Rochester N,V, ailitance of 280 i

‘This one-way crit utiliged at New Yee the transaante trans-
suiting felts foe printing tlegrap described above with the ex
=
AppLicavton OF painrine Taneunaes 0

ception that automatic tanemision froma perforated tape for operat=
ing mie celetypenriters was eubeluted for tke manta keyboard
method foe aperating tape printers ordinarily used

“At Rorky Point the power of the radio erausmiter was greatly
eduvel for these tests. The average nawer ranted in che direction of
Fochester was equivalent ¢o 0.7 Blewate radiated feom a nmtives=
tienal antenna. ‘The average deviation om ee valve was less haa 1
Ub. Under these conditions the average Held receive in Rochester was
{225 db wine one microvele per swder. The average cleviation from
this mean value yas ese thax 2 db, A daily bol-honr tess was made
in te aerncan or evening at time wo chosen a5 t0avuid the sunset
perl of disturbed rio ansssssen

‘Ar eachene:, laboratory type eecciving euiment was emplnved
for picking up the radi sgaale and dermslulating chem to vite fe=
quencies, The voice frequency sigmle wee Uren wsed to oprrale
Standard voice Gsueney carrier termaal cquipment at: Rochester.
‘This was modified for two-tone operation in 2 manner sila to chat
shown forthe tnusetlantie receiving, tevrinal ia Ti.

“The tclerypewriter signals were sent out from New York at 60
‘worls per minute from an automatic sae tanamiteer. ‘The eupy re=
‘even ver the eee circu was subsequently compared ith smal
Lseously recorded crny which was not vext over the radio crit
Keyboard errors wsieh occur eceninually in perferaing the tye for
‘zntomasie Lransmiselon appesvnd im both copies. Disergaediag these
rors anil counting al wie Wid aot appear on bot copie, it a
fosdble to cls che percent of errs ame Ly 1adio ronson,
During the hall-our daily test period, sbout 10000 characters were
ents Tels apparent ast ree of errr hc were lee an bout 0.
ppt cenc coud not be ceermined serrate!

‘Before making ts half-hour test each day to determine the pe cent
of erors recived ut Rochester, meszremente were made i the amount
[Cr siznal snd of asic in the otpot ofeach woizefeecueney Mer ‘The
‘Senl-uo-noice raro thes mssurel Was ogsured to Be the val o>
Taarg ever the soneeding half hour of lest. The nacure of these
ineesurements was such thatthe data were sqmewhar scattered. How
Ger, by suitable smonthing procedives che spprownate curve shown
Sn ig. Sw ole

‘At lleulton, Maine, routine radi nee“ cvervations are made four
times each day on ke antenna and Hoarly of the svave-antenna,
Cystenn as nat of the operating prosalire in maintaining tamsalae
Te telephone services" [e epemed detralle to nd cue wherher Tie
data which extend over several years could be util 1 extrapolate