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BELL SYSTEM TECHNICAL JOURNAL 



inner streams and currents of 0.5 and 0.8 milliampere, a gain of 40 db at 200 

 Mc due to the double-stream amplification was predicted, with bandwidth 

 to 3 db points of 90 Mc, centered about 200 Mc. A later estimate, in- 

 cluding the effect of the separation of the hollow beams in space, reduced 

 the 40 db figure to 23 db. 



Prediction of the performance of the device as a whole also requires an 

 evaluation of the couphng of the helix sections to the electron stream. The 

 length of the active portions of the helix sections was chosen to give gain of 

 order unity as estimated from single-stream traveling wave amplifier con- 

 siderations for the proposed operating current. 



Fig. 3 — Power output versus power input for double-stream amplifier at 200 Mc with 

 beam potentials of 54 volts and ii volts and 1.1 ma current in each beam. 



3. Experimental Observations 



The two beam potentials and the two beam currents were varied until 

 good operating conditions were reached. In the amplifier tube with helix 

 output, good operation with 29 db gain at 200 Mc was observed at low input 

 signal levels with inner beam potential 54 volts, outer beam potential 2>i 

 volts, and 1.1 milliampere current in each beam. Measurements of output 

 and input signal power are shown in Fig. 3, in which output power is 

 plotted as a function of input power. The gain is seen to be constant at 

 29 db from low levels up to an output power of 0.03 milliwatts, at which 

 point compression sets in. Maximum power output is 0.3 milliwatts. 



