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BELL SYSTEM TECHNICAL JOURNAL 



coil forming the "inductance" of the circuit. Such a resonator behaves 

 just as do other resonant circuits. Power may be derived from it by means 

 of a couphng looj) hnking the magnetic field of the single turn coil. An 

 electron stream of uniform current density leaves the cathode and is shot 

 across the "gajV' between the two grids, traversing the radio-frequency held 

 in this gaj) in a fraction of a cycle. In crossing the gaj) the electron stream 

 is velocity modulated; that is, electrons crossing at different times gain 



ZERO — 

 EQUIPOTENTIAL 

 SURFACE 



OUTPUT LINE 



Fig. 1. — An idealized reflex oscillator with grids, shown in cross-section. 



different amounts of kinetic energy from the radio-frequency voltage across 

 the gap." The velocity modulated electron stream is shot toward a negative 

 repeller electrode which sends it back across the gap. In the "drift space" 

 between the gap and the repeller the electron stream becomes "bunched" 

 and the bunches of electrons passing through the radio frequency lield in 

 the gap on the return transit can give up power to the circuit if they are 

 returned in the proper phase. 



^ The most energy any electron gains is jiV electron volts, where V is the peak radio 

 frequency voltage across the gap and /3 is the "modulation coelTicicnt" or "gap factor", 

 and is always less than unity, /i dci)ends on gap configuration and transit angle across 

 the gap, and is discussed in Appendix II. 



