Hi Alan,
Do you mean you can retune the Xtal to one of its component harmonics? Can
one ever make an oscillator that oscillates at a non harmonic component?
                                                John

                -----Original Message-----
                From:   Alan Pearce [mailto:A.B.Pearce@RL.AC.UK]
                Sent:   Thursday, 23 March 2000 8:50
                To:     PICLIST@MITVMA.MIT.EDU
                Subject:        Re: Series R in Xtal line

                >Many thanks for your reply. It makes a little more sense
now, although I
                >still don't understand why the oscillation can resonate at
the XTALs
                >fundamental. Is it because the amplifier has a tuned
maximum frequency
                >dictated by the Xtal?

                The fundamental frequency of the crystal will most likely
have a lower ESR or
                higher parallel resonant impedance than at any of its
harmonics. This will most
                likely be true for a crystal which has been made to work at
a harmonic as well.
                Also the amplifier portion of the oscillator will have
higher gain at the lower
                frequency. The whole combination will try and work at the
easiest point at which
                it will oscillate, which will then tend to be the lowest
frequency because that
                is where the highest gain and best response is. Any attempt
at getting a crystal
                to work at a harmonic (overtone) will involve another tuned
circuit at that
                frequency to make that the preferred operating frequency for
the crystal.