
127
The capacitance required to tune the coil to 300 kHz, or 0.3 MHz,
is (Sec. 8.7, footnote) C = 25
333//V
2
L = 25 333/(0.3
3
x
1
200) =
235 pF. This, of course, includes the tuning capacitor itself plus the
stray capacitance of the wiring and of the coil. The whole of this is
equivalent to a perfect 235 pF in parallel with a resistance of, shall
we say, 0.75 ΜΩ (Fig. 8.12c). The reactance, X
0
is bound to be
same as X
L
at resonance; but to check it we can work it out from
\/2nfC = 1/(2π x 0.3 χ 0.000235) = 10
6
/(2π χ 0.3 χ 235) =
2260 Ω. Qcis therefore
R
c
/X
c
= 750000/1260 = 332.
If the two components are united as a tuned circuit, the total