382 BELL SYSTEM TECHNICAL JOURNAL 



afforded by their use greatly outweigh any such troubles. These 

 advantages may be summarized as follows: 



1. Suppress echoes and singing which would otherwise be heard 

 due to adjustments to reduce radio noise, instability and cross-trans- 

 mission paths. 



2. Prevent retransmission of echoes which would cause overloading 

 and two-way broadcasting at the radio transmitters. 



3. Save privacy apparatus. 



4. Permit the telephone listeners to hear louder speech waves. 



5. Afiford independent technical operation of the two ends of the 

 circuit. 



i 



