Hi all,

I have a colpitts crystal oscillator with a 16.000 MHz parallel
resonance crystal that I'm turning into a FSK modulator with the
addition of a varactor / varicap diode. Two questions:

Originally, I had the varicap diode in parallel with the crystal. This
caused the oscillation to significantly attenuate (10 dB or so) as I
pulled the crystal 1 - 2 kHz. I found a reference design of a Hartley
oscillator that had two varicaps in series with a resonance capacitor,
so I decided to give this a try. This works a lot better, attenuating
my 1Vpp oscillation about 100mVpp. Why does the series configuration
work so much better?

I'm at home where I only have an analog tektronix 2213 60MHz scope (no
spectrum analyzer). How can I measure the frequency deviation / pull of
the crystal with the series configuration? Any ideas?

Cheers,
Chris