1052 



THE BELL SYSTEM TECHNICAL JOURNAL, OCTOBER 1951 



receiving converter, IF preamplifier, delay equalizer, IF main amplifier, 

 transmitting modulator and transmitting amplifier. The lower half of the 

 bay contains four 19-inch wide oscillator and control units. These units, in 

 the case of a main station repeater, are two microwave generators, a receiver 

 control unit and a transmitter control unit. In the case of an auxiliary 

 repeater, one of the microwave generators is replaced by a panel contain- 

 ing a 40-megacycle oscillator and shifter unit. All connections to the 

 units of the bay are made by means of plugs and jacks for easy servicing. 

 A repeater receives a frequency modulated microwave signal at a normal 

 level of about —38 dbm and transmits it at +27 dbm. Upward fades of 

 5 db and downward fades of 25 db are compensated to within about 1 db 

 by automatic volume control action within the repeater. The amplitude 

 characteristic is maintained flat to within 0.2 db over a 20-megacycle band. 



10 5 5 10 



FREQUENCY IN MEGACYCLES FROM MIDBAND 



Fig. 9— Delay distortion & amplitude characteristics. 



The amplitude and delay distortion characteristics of a repeater bay with 

 and without delay equalization are shown in Fig. 9. 



C. Radio Receiver 



A channel separation network, as shown in Fig. 7, is required for each 

 receiving channel. The network separates a particular channel from the 

 six incoming 20-megacycle bandwidth channels for individual amplification 

 and equalization in the repeater. It consists of two hybrid junctions and 

 two band reflection filters which are tuned to the frequency band to be 

 separated. An incoming signal is spHt into two parallel paths in passing 

 through the first hybrid. A reflection filter in each of these paths returns the 

 energy of the channel to be dropped to the first hybrid. By making the elec- 

 trical path lengths from hybrid to filters differ by J wavelength at the fre- 

 quency of the channel to be dropped, the reflected signals are in phase op- 



