REFLEX OSCILLATORS 



587 



temperature Tq corresponding to zero bombardment power divided by the 

 rate of heat loss at this temperature. This indicates a rather paradoxical 

 result, that the temperature for zero bombardment power should be as high 

 as possible. This arises from the dependence on radiation cooling. We are 

 limited in setting the value of To by the form of the function F^ , which 

 requires that the reduced temperatures T^c and Tsh should be very large 

 compared to 1. Since the true temperatures corresponding to these reduced 

 values must simultaneously be small compared to Tm , it is apparent that 

 we are not completely free to make Tq large, and a compromise must be 

 worked out. 



8800 9000 9200 9400 

 FREQUENCY IN MEGACYCLES PER SECOND 



Fig. 81. — Variation of the frequency of resonance vs gap displacement for the W.E' 

 2K45 resonator. The vertical lines show the required tuning range. 



In determining a practical design for a thermal tuner, the first charac- 

 teristic which must be known is the variation of the resonant frequency of 

 the oscillator cavity as a function of gap displacement. It is apparent that, 

 for the highest speed of tuning, the rate of change of frequency with gap 

 displacement should have the maximum possible value. However, this 

 tuning characteristic is dictated by the performance requirements of the 

 tube as an oscillator and hence is not available as a variable in the design. 

 Fig. 81 shows the variation of frequency with gap displacement for the 

 2K45 resonator. The required range is indicated. 



When the required motion is known a choice may be made of a mechanism 



