TD-2 MICROWAVE RADIO RELAY SYSTEM 



1043 



contemplated that by the end of 1951 there will be over 20,000 broad-band 

 channel miles of radio relay in operation in the Bell System. Of this, about 

 two-thirds will be used for television service and one-third to provide over 

 600,000 circuit miles of telephone circuits. 



II. TD-2 System — General 



A radio relay system designed for long distances involves many problems 

 new to radio but not new to long distance wire circuits. These problems are 

 chiefly those of systems engineering to close transmission tolerances be- 



4200 r— 



Q 



O 4150 



ai 

 <n 



CC 4100 



a 



^ 4050 



>- 

 u 



< 4000 

 O 



UJ 



Z 3950 

 o 



< 3900 



5 3850 



< 



O 



2 3800 



O 



2 



2 3750 



O 



U 



3700 



4170 

 4130 

 4090 

 4050 

 4010 

 3970 



3850 

 3810 

 3770 



STATION A 



STATION B 



3930 <h-(TL^{T}-^ 



389o^-[Xr^[KM 



3730 ►— {r)''''^^^^{r]-< 



W-E 



CHANNEL 6 



E-W 



80 MC 



40 MC 'X^ 



w-E HZKv^^^{KH 



20 MC GUA RD B AND 



CHANNEL 1 

 E-W 



Fig. 2 — TD-2 radio frequency plan. 



cause of the many repeaters in tandem. To insure satisfactory systems opera- 

 tion, the transmission characteristics must remain stable over long periods 

 of time to permit unattended operation. A reliable power plant and an alarm 

 system are essential parts of the radio system. 



A. Description 



The TD-2 Radio System utilizes frequency modulation and provides 

 twelve broad-band channels, six in each direction, spaced 40 megacycles 

 apart in the 3700-4200 megacycle common carrier band. A frequency assign- 

 ment chart is shown in Fig. 2 and a systems block diagram in Fig. 3. Two 

 broad-band channels in opposite directions provide a two-way message 



