
156 Analog Circuits Cookbook
and note the frequency at which resonance is indicated. Now increase the
capacitance to 33 pF and repeat the procedure. From these results, the
method shown in 'Quantifying internal capacitance', later in this section,
will give a close approximation to the test circuit's true internal capaci-
tance. Knowing this, the various combinations of the 100 pF capacitors
can be used to calibrate the HI and LO scales, making due allowance for
the internal capacitance. The spot test frequencies of 250, 790 kHz, 2.5,
7.9, 25, 79 and 100 MHz should now be set up, by adjusting the cores of
L\
to Zg respectively. For this purpose ...