Newnes Radio and RF Engineering Pocket Book, 3rd Edition

97

and the mounting arrangements. C

0

, typically 3 –15 pfd, represents

the shunt capacitance of the electrodes in parallel with the can capac-

itance. If the oscillatory current is considered, the resonant frequency

is decided by the values of C

0

in series with C

1

, L

1

and R

1

,and

all crystals basically resonate in a series mode. Figure 7.2 illustrates

the changes in impedance close to resonance. However when a high

impedance, low capacitance, load is connected across the crystal ter-

minals it behaves as a parallel tuned circuit exhibiting a high resistance

at the resonant frequency. A crystal operating in the parallel mode

oscillates at a higher frequency ...