632 



BELL SYSTEM TECHNICAL JOURNAL 



Signals come in on input circuit A to modulator lA which modulates 

 125 kc from which crystal filter A selects the upper sideband. This 

 upper sideband then goes into modulator 2 where it modulates 2500 kc. 

 The sideband in this case will be located more than 125 kc away from 

 the carrier and can be selected by a relatively inexpensive filter which 

 now delivers the single sideband in position 2625.1 to 2631 kc to 

 modulator 3. In modulator 3 this sideband modulates a suitable 



EXTENSION TO TWIN CHANNELS 



ASSIGNED 

 FREO, F 



VOICE 



CHANNELS 



r-: H 6.0 KC. 

 ■r: I a 



4 0,1 KC. 



125 KC- 



g 



MOD. 

 lA 



CRYSTAL 

 FILTER A 

 125,1-01 KC 



131.0 KC, 



125.1 KC. 

 124.9 KC. 

 119.0 KC. 



fd 2631.0 KC 



Ji 2625.1 KC 



2625 KC. ,^ 25249 ^f- 



'-12619,0 KC 



INPUT.B 4 MOD M^ CRYSTAL 



'B ; ;il9-l24,9KCi 



>■ 



I 



I 



CARRIER 

 RE-SUPPLY 

 AMP 125KC 



MOD 

 2 



125 KC. 

 MULTI- 

 VIBRATOR 



625 KC. 



CRYSTAL 



OSC. 



2500 KC, 

 HARM. 

 GEN, 



2625 KC. 



MON. SUPPLY 



MOD. 



I 



2619-2631 KC 

 B P FILTER 



CASE n 

 F> 1 0,000 KC 



jF+6.0 KC 

 ' F + 0,1 KC 

 ^ F- 0,1 KC 

 ' F-6.0KC. 



CASE I 

 F<10,000 KC 



MOD 

 3 



AMP. 



HARMONIC 

 CEN. 



CASE I,f-F+2625KC. 

 'cASEn,f-F-2625KC. 



CRYSTAL 

 OSC 



CRYSTAL 



FREQUENCY 



AMP. 



HARM 

 GEN. 



TO ANTENNA 



-OR ADDITIONAL 



AMPLIFIERS 



1ST. 

 DET 



2ND 

 DET 



^MONITOR 



"output 



2625 KC. 

 AMP. 



Fig. 13 — Single sideband transmitter circuit. 



frequency which may be anywhere from 6 MC to 20 MC which is 

 secured from a suitable source such as the harmonic output of a 

 crystal oscillator. The output of this third modulation places the 

 single sideband in a desired position in the ether whereupon it passes 

 through an amplifier to an antenna and is radiated. This desired 

 position in the ether may be either above or below the final carrier 

 frequency as may be found desirable, depending upon the frequency 

 range in which operation is to occur at that particular hour. 



