[time-nuts] How far can I push a crystal?

[Ed Breya]

Maybe I should clarify what I meant by pushing the crystal frequency. I 
meant only using various topologies and electronic components in the 
associated circuitry, that would detune it from its natural resonance 
far enough to reach the new frequency, and still have it be sort of a 
narrow-bandwidth crystal oscillator - not doing any mechanical changes 
to the crystal element itself.

Since the ceramic resonators seem to work well, and can be pushed (or 
pulled?) fairly far away by proper selection of the associated component 
values, I was wondering how far quartz crystals can reasonably go. I 
encounter this situation often - needing an oddball frequency, but 
preferring to use common or standard parts. The nominal choices in 
ceramic are quite limited, while in crystals, there are many more - but 
few ever seem to land at or near enough to a frequency I need.

The only thing I have thought of so far is to maybe add some series R to 
drop the crystal Q, so broadening the resonance, and just dragging it up 
by extra series C, but at some point there's no point to even having the 
crystal there at all. I'm just trying to figure out what's possible and 
reasonable.

I know that I can get any custom frequency by spending enough money, but 
that takes the challenge and fun out it sometimes.

Ed