244 



BELL SYSTEM TECHNICAL JOURNAL 



The second set of curves, shown in Fig. 12, were taken with an 

 "L" tube (101-D) but with two input frequencies oi Q = 5,000 and 

 P = 13,000 cycles appHed simultaneously. The measurements in 



z.o 



o 



% 1.& 



o 



2 



\.2 



1.0 



2 4 C S 



MILL I AM PERES INPUT OF P AND Q 



10 I? 



INTO tOO*^ 



14 15 



Fig. 12 



this case were made on the modulation product consisting of the differ- 

 ence frequency (-P — <2) = 8,000 cycles and of the second harmonic of 

 Q, IQ = 10,000 cycles. Such curves furnish a quick and accurate 

 means of studying the performance of the vacuum tube and also afford 

 a convenient check on mathematical computations which, in this 

 particular case, with a two frequency input, have indicated that the 

 difference frequency amplitude should be twice that of the second 

 harmonic. 



