TD-2 MICROWAVE RADIO RELAY SYSTEM 1057 



monic generator stages, three doublers and three triplers. Only a few miUi- 

 watts of output power is required where the generator is used for the re- 

 ceiver beating oscillator alone, as in main stations or terminals. Here the 

 final multiplier is operated as a sextupler, thereby permitting the ehmination 

 of the penultimate stage. At an auxiliary repeater, the receiving beating 

 oscillator source is obtained from a 40-megacycle shifter converter, one input 

 of which is from a part of the microwave generator output, and the other 

 is from a crystal controlled 40-megacycle generator. 



F. Transmitter-Receiver Interconnections 



At auxiliary stations the IF output of the receiver is connected by a short 

 coaxial line and 5 db resistance pad directly to the transmitting modulator 

 in the same bay. This resistance pad is used as an impedance matching aid. 



At main repeater stations the IF receiver output and the transmitter input 

 are carried in coaxial lines to IF patching and switching equipment. With 

 30 to 60 feet of coaxial line between the receiver and transmitter, impedance 

 match requirements are more severe than for short coaxial Hne connections. 

 Here, a 6 db resistance pad is connected in the output line of the receiver 

 and a 3 db resistance pad and buffer amplifier are connected in the input 

 line of the transmitter modulator. The buffer amplifier consists of a single 

 stage using a 418A tetrode and its gain may be set manually to provide 

 — 1 dbm to +5 dbm of signal power into the transmitter modulator as 

 required. The bandwidth of the amplifier is approximately 20 megacycles 

 and is sloped in such a manner as to approximately compensate for the small 

 variation of loss over the band in the patching coaxial lines. 



G. IF Switching* 



IF switching circuits are provided at terminals and main repeater points 

 to facilitate maintenance operations as well as to provide flexibiUty for the 

 changing requirements of network distribution. These switching and dis- 

 tributing operations are obtained by the use of unity gain amplifiers which 

 are designated IF switching amplifiers and IF distributing amplifiers. 



An IF switching amplifier functions as a single-pole double-throw switch 

 for connection between intermediate frequency circuits of 75-ohm impedance. 

 It has two input networks, each connected to a grid of a 404A pentode. 

 The plates of the two tubes are connected in parallel to the output. Trans- 

 mission through one or the other of the tubes is prevented by the apphca- 

 tion of a high negative grid bias to that tube. Switching the bias from one 

 tube to the other thus permits the selection of either input signal. In most 



* Prepared by T. R. D. Collins. 



