34 BELL SYSTEM TECHNICAL JOURNAL 



tube working as a class A amplifier and the second tube under class B 

 conditions an output of over ten watts has been obtained with a second 

 stage plate efficiency of around seventy per cent and with an over-all 

 voltage gain for the two stages of twenty-four decibels. Using the 

 first tube as a harmonic generator, driven at fifty megacycles, and the 

 second tube as a class B amplifier, over six watts of 150-megacycle 

 power have been obtained with an over-all voltage gain from fifty- 

 megacycle input to 150-megacycle output of about four decibels. 



Conclusions 



It is often little realized how completely our present highly de- 

 veloped technique of making communications measurements depends 

 upon our ability to set up stable and reliable amplifiers at the frequen- 

 cies we wish to use. We are now in a position to set up such amplifiers 

 in the ultra-short-wave range; amplifiers of sufficient gain, stability, 

 and most important, of sufficient power handling capacity to enable 

 us to make many of the measurements we may wish, at low enough im- 

 pedance levels to minimize some of the effects of unavoidable stray in- 

 ductances and capacitances in our circuits and at high enough power 

 levels to make practicable the use of simple and reliable, and almost 

 necessarily rather insensitive measuring apparatus. Furthermore, our 

 experience in this work indicates that it is not necessary to modify 

 drastically our experimental procedures when we move into the ultra- 

 short wave field. Much more care in circuit design is required, but 

 with more attention to details formerly unimportant, much of the 

 background of electrical measuring technique becomes, with the advent 

 of this new tool, available in the ultra-short-wave range. 



