DESIGN FACTORS OF THE 1553 TRIODE 



529 



different in principle, but would be harder to carry out in practice be- 

 cause of the helical geometry. The value can of course in any case be 

 found by measurement of the tuning admittance as a function of fre- 

 quency. From these equations the circuit degradation factor can be calcu- 

 lated, and is shown in Fig. A2-3 as a function of frequency. 



The accuracy of the coaxial line assumptions decreases as the cavity 

 becomes shorter. For 4000 and 6000 megacycles, since the length of the 

 cavity is less than its diameter, it would be more nearly correct to regard 

 it as a radial transmission line loaded by the inductive "nose" in the 



0.9 



15 0.4 



0.3 



0.1 



2000 3000 4000 5000 



FREQUENCY IN MEGACYCLES PER SECOND 



Fig. A2-3.— Capacitance degradation factor, 



C22 + 



center. The admittance of such a cavity can be calculated^^ or measured; 

 but the additional precision hardly warrants the effort in the present case. 

 The capacitance degradation factor at 4000 megacycles is indicated from 

 Fig. A2-3 as .81, or only 0.9 db less than the intrinsic limit of unity if the 

 passive capacitance were entirely negligible compared to the active 0.5 

 ii\ij. This indication is somewhat optimistic, as appears from Fig. A2-2. 

 The coaxial line formulas assume that the capacitance corresponds to a 

 radial electric field between concentric cylinders A and B. This capaci- 

 tance is found to be quite small (.11 ii\ij at 4000 Mc). The actual lines of 



** S. Ramo and J. R. Whinnery, "Fields and Waves in Modern Radio," N. Y., Wiley, 

 1944. 



