TD-2 MICROWAVE RADIO RELAY SYSTEM 1049 



practical triode amplifier for microwave application^ • ^ was instrumental in 

 determining a pattern for redesign, for it suggested the possibility of greatly 

 simplifying the repeater while at the same time providing wider transmission 

 bandwidths at greatly improved efficiency. By replacing the high voltage 

 klystron (velocity variation type) amplifiers of the early repeaters with the 

 new low voltage triodes, it became practical to design the system for battery 

 operation — an important step toward increasing the system's reliability 

 as it removed regulated rectifier tubes from the vulnerable portion of the 

 system and eliminated the problem of hits during switchover from com- 

 merical to standby primary power. In the TD-2 System, vacuum tube heaters 

 are generally operated from a 12-volt battery through dropping resistors, 



Fig. 7 — Channel separation network. 



thereby approximating constant heater power operation to increase tube 

 life and rehability. 



B. Repeater Description 



A block diagram of a TD-2 repeater is shown in Fig. 3. An incoming micro- 

 wave signal from a receiving antenna is selected by a channel separation 

 network shown in Fig. 7. The signal is then combined in the receiver con- 

 verter with energy from a beating oscillator source to provide an intermediate 

 frequency signal band centered at 70 megacycles. Amplification, delay equal- 

 ization and automatic gain control take place at the intermediate frequency 

 of the radio receiver. In the transmitter this signal is combined in the trans- 

 mitter modulator with a microwave source to provide a band offset 40 

 megacycles from the received frequency band. This signal is ampUfied and 

 combined through transmitter channel separation networks with signals 



