DESIGN FACTORS OF THE 1553 TRIODE 



525 



Al-3, it will normally be constant for low power levels (for which the 

 device is essentially linear) and equal to the low level power gain | F |'^ . 

 However, at some higher power level non-linearities appear in some or all 

 of the various short-circuit admittances, usually causing the power gain 

 to decrease below the small-signal value by an amount called the com- 

 pression, C. If Po/Pi be power gain for any power output and | F |- 



10 12 14 16 



POWER OUTPUT IN DBM 



Fig. Al-3. — Typical gain variation with power output. 



DC OUTPUT CURRENT 



Fig. Al-4. — Compression vs. 



Alternating current in output 



Direct current in output 



the small-signal power gain, the compression C is defined in decibels as 

 follows: 



C = 10 logio 

 = 10 logio 



10 logio Po/Pi 



(Al-18) 



Pi 



Naturally, the compression depends upon how hard the tube is driven. 

 It is therefore a function of the amount of drive, which may be con- 

 veniently expressed in terms of the ratio of the alternating output cur- 

 rent to the operating direct current, as in Fig. Al-4. 



