1360 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1954 

 2.0 



2.5 



Fig. 13 — In a double-stream amplifier, gain is obtained when the phase con- 

 stants of the slow wave of the faster stream and the fast wave of the slower stream 

 are nearly equal. 



large the maximum is. For an ordinary two-potential electron gun, ^max 

 is very large compared ^\dth ?'min . 



NOISE DEAMPLIFICATION 



Early traveling-wave tubes made use of a two-potential electron gun 

 spaced a critical distance from the circuit, as shown in Fig. 14. More 

 recently it has been found possible to reduce the noise figure considerably 

 by the use of space-charge-wave amplification, as discussed in the sec- 

 tion on "The Space-Charge-Wave Amplifier." The structure used is 

 indicated in Fig. 15. The gun has a low-potential anode followed by a 



kGUNj-L^ir. 



Fig. 14 — When a simple, two-potential electron gun is used, the noise figure 

 of a traveling-wave tube can be optimized by adjusting the drift-space between 

 the gun anode and the helix. 



