158 BELL SYSTEM TECIISICAL JOURNAL 



Since it did not seem practicable to (le\eiop a carrier frequency 

 transformer suitable for conneclinj; between phases of a high voltage 

 power line it was decided to cou|ile to the power line by means of 

 capacity. Two general tyjies of condensers are possible, first, a con- 

 centrated capacity condenser and second, a distributed capacity 

 condenser. A concentrated caiiacity condenser suitable for direct 

 connection to a high voltage power line was not available, but its 

 development has been successfull>- undertaken by the Ohio Brass ("o. 



^ FI?EOUENCy IN KILOCYCLES 



c ioco)o«o»oMio8090iooiioiui3ai40iaciurro 



Fig. 5— Xoltagc .Viiiplifiiation Characteristic of High Frequency Transformer 



The distrilnited rapacity was obtaiiietl by suspending a wire ixiralle! 

 to the power conductor and employing this wire as one plate of the 

 condenser and the conductor as the other plate. Both of these meth- 

 CKJs of connecting to the power line have been developed and are 

 described later. 



Dksicn ni- Tiiic C'akkikk Moiipmknt 



.■Mtiiough the "carrier suppressed" system has nian\' ad\antages 

 over the "carrier transmitted" system, the dilTftcullN- of securing filters 

 suitable for suppressing the unwanted products of the modulation 

 prevented the use of the carrier suppressed system. 



Several general characteristics of the electrical and mechanical 

 design of this carrier e(|uipmcnt are worthy of note. The \'arious 

 stages of vacuum tubes in both the transmitting and receiving cir- 

 cuits are coupled b\- transformers. These transformers are closed 

 iron core coils using the standard core employed for audio-frequency 

 transformers. Kig. .") shows the characteristic of one of these traiis- 

 formers, and it is e\'ident from this figure that the variation in am- 

 plification from '\i\ K ( " |M I "id K (\ Is only a fraction of a trans- 

 mission unit. 



