[time-nuts] Square to sine wave symmetrical conversion (part 2)

[jerry shirᴀr]

Thanks Tim.  I love reading these papers.  However my copy states "In fact,
were it not for this slight non-linearity, it would be virtually
impossible to build a simple lamp-stabilized RC oscillator with good
envelope stability over a wide frequency range." rather than "In fact, were
it not for [amplifier] nonlinearity, it would be impossible to build a
simple oscillator with good envelope stability."  The meaning changes a
little bit.

Thanks Bob,

Even looking at Tim's article, they are talking about a low degree of
distortion with an RC oscillator.  I am assuming that the Q of the RC would
be quite low with respect to the overtone crystals you speak, and yet the
RC oscillator described here has low distortion from the oscillator stage.

Putting a filter in the feedback path with the high Q crystal seems like
you would be de-Q-ing the crystal and losing the high Q characteristics of
the crystal.  Any changes of filter components over time seems like it
would necessarily add drift to the oscillator.  What do you think?  Of
course I am not saying that you can't put filters in the crystal circuit
but rather that is something I would never recommend doing that in a
precision oscillator design.

I realize what the impedance plot looks like of AT-cut and SC-cut crystals
but my question was specifically about harmonics.  That is the topic of
this thread.  Are you thinking that crystals are rich in harmonics?  I am
not really seeing an idea of where you are saying the harmonic components
come from in these high precision oscillators in the oscillator circuit.

What are the "impedance properties" of the crystal?  Why use a crystal
rather than slapping a cap and a coil in there to get your desired
frequency?

When you "pick off" the collector current, wouldn't that include the
amplified base to emitter junction noise inherent in simple transistor
oscillator circuits?  Would that be the same as the crystal current?

Thanks.

Jerry