TF.l.F.rilOSE IR.IXS.MISSI(K\' M.IIM l-X.IXCE 27 



Clark.' RrftTiiur in ilii-sf pajH-rs w.is also luaiic In tin- ^latulartl 

 OM-illators UM'<I ii) suppKiiij; llu- inrasuriiin riirn-nts for the suls. 



I- .-1 'I'ransniission .\/c«.v«r/Hi; Set. This is an "car h.ilanci'" 

 jHirtablo set siiitaMi' for loop traDsinissioii li-s(iiin only and (li'si^;iu-(l 

 primarily for ifstiiii; i-tiiiipincnl .iiul ciicnits in the •^in.illiT irntr.il 

 ofTices. 



3 — A Transmission .\ffasiirinii Set. This i> a "nu-irr halanci- ' 

 portable set suit.ibk' for both loop and strainlu.i\va\ I raiisniis^ion 

 testing and designed priniariK' for letting circuils and e(|uipnient 

 in the larger eenirat otViees. 



4 — .-1 'I'ranstnission Maisurinti Scl. This is a "niL-ler balance" set 

 suitable for both loop and straightaway' transmission testing and 

 designed for (H'rmanent installation al the larger toll otfu'es i)rini,iriK 

 for testing toll eireiiits. 



2 — .1 Citin del. This is a "meter balanre" set designed lor miMsiir- 

 ing amplifier gains. 



Certain other testing methods in addition to Noliime cfficiencN' 

 tests are also extensiveh' used in transmission maintenance work 

 and some of the more import. int of these are lirietK' discussed in 

 .Ap|H;iuli.\ .A of this paper. 



Since the routine procedures in testing toll circuits using the above 

 apparatus ditTer considerably from those followed in the local or 

 exchange area plant, the toll and local practices have been considered 

 separately in the following discussions: 



Transmission Tests on Toll Cik( ins 



The importance of having available means for ([uickK checking 

 the transmission efificiency of toll circuits and of economicalK' main- 

 taining the proper standard of transmission is evident when it is 

 considered that in a plant such as that operated by the Bell System 

 there are at the present time more than 20,000 toll circuits in service. 

 The circuits making up this system are of various types and con- 

 struction, depending on the service requirements and length, and 

 also upon certain other factors determined In- engineering and 

 economical design considerations. 



From the standpoint of maintaining transmission etticiency between 



toll offices, the various types of toll circuits can be di\ ided into three 



general classes: one, non-rcpeatered circuits, two, circuits equipped 



' F. H. Best, "Measuring Methods for Maintainini; the Transmission EtTiciency 

 of Telephone Circuits," Journal of the A. I. E. £., February, 1924. .\. B. Clark, 

 "Telephone Transmission over Long Cable Circuits," Journal of the A. I. E. E., 

 January-, 1923. 



