618 



BELL SYSTEM TECHNICAL JOURNAL 



first even though either or both of the radio equipments be entirely 

 outside of the manual control of the speakers and be many miles 

 away. The problems involved have given rise to the development 

 of many pieces of apparatus which are seldom used in the broadcasting 

 field. It is the intention, therefore, in this paper to review some of 

 these devices and tell briefly why they are used and what they do. 



To begin with, attention is called to three diagrams in Fig. 5. These 

 three diagrams indicate three of the many ways in which a transmitter 



W 



VOGAD COMF'ANC;Or< TRANS. 



V 



CALLING 



1PAND0R CODAN RECEIVER 



V 



TRANS. 



"- -KJa 



RELAY 



V 



REC. 





^fi_ 



CALLING 



VOGAD 



TELEPHONE 



LINE 



DIRECTIVE 

 iJJl'' ANTENNA 



A WIRE 



TERMINATING 



CIRCUIT 



-<xxx> 



CALLING CCWPANDOR CODAN RECEIVER MUSA 



Fig. 5 — Three arrangements of radio terminal apparatus are shown herein. 



and a receiver might be connected with'associated apparatus for one 

 end of a radio link. Two of the diagrams indicate connection to a 

 telephone line which may extend more than 3,000 miles to a sub- 

 scriber. The third circuit indicates an arrangement which is custom- 

 ary on small boats, sometimes in aircraft, and other places where a 

 partially trained operator is available and is the one using the device. 

 It is to be observed first of all that in two of these diagrams the input 

 to the transmitter and the output of the receiver are connected to 

 the same telephone line. This necessary connection leads to dififi- 

 culties. Signals from a subscriber on the telephone line operate the 



