1076 THE BELL SYSTEM TECHNICAL JOURNAL, OCTOBER 1951 



D. -24 Volt Supply 



A — 24 volt battery plant utilizing a regulated selenium charging rectifier 

 capable of 6-ampere constant load supplies power for the alarm and order 

 wire circuits. Voltage regulation is obtained by saturable reactors in a 

 magnetic type of regulating circuit. This plant is shown as the extreme left 

 bay in Fig. 23. 



E. Engine Alternator Reserve Plants 



The main route of the TD-2 system normally requires reserve engine al- 

 ternators of 20 or 30 kw capacity. The initial sets used were of the automatic 

 gasoline engine alternator type available in 20 to 60 kw capacity. The 

 engines are fully automatic in operation. They accept the load after a pre- 

 determined period of commercial a-c. service failure and restore the load to 

 the commercial service when it returns to normal. They are capable of long 

 hours of operation under emergency conditions. Numerous alarms are 

 available in the engine plant to indicate its status under all conditions. Re- 

 cent development has made plants available similar to those mentioned 

 above which are powered by automatic diesel engine driven alternators. It is 

 expected that this latter type of engine will be used in the future where 

 capacities of 20 kw or more are required. 



VIII. Conclusion 



The New York-Chicago section of the TD-2 transcontinental radio relay 

 system was opened for service with the transmission of television network 

 programs on September 1, 1950. The system was extended to Omaha on 

 September 30, 1950. Similar systems were put into service during September 

 between New York and Washington and between Los Angeles and San 

 Francisco. 



By the fall of 1951 a transcontinental microwave radio relay system will 

 be in service between New York and San Francisco carrying television 

 programs and hundreds of telephone messages. This system will augment 

 present intercity toll facilities and, in conjunction with coaxial cable, will 

 provide a nationwide network of broad-band channels capable of handling 

 television transmission or large groups of telephone circuits. 



The growth of broad-band channels during the next few years can be 

 handled by the addition of channels to partially loaded TD-2 Systems and 

 by new routes. Further expansion of radio relay systems into higher fre- 

 quencies, 6,000 and 10,000 megacycle bands now set aside by FCC for com- 

 mon carrier use, appear to offer room for further expansion of systems 

 comparable to TD-2. 



