[Milsurplus] Crystal History Book and tips on etching

[Dennis Monticelli]

The book I have is "Crystal Clear" by Thompson, IEEE Press 2007.  It goes
into a lot of detail describing the transition from a cottage industry to
the most extensive in the world during WW2.

As for the technique of stabilizing FT-243s, it is attributed to
Bliley, although I wouldn't doubt that others discovered it as well because
it was essentially discovered by accident.  Bliley used HF etching for the
final small move to the design frequency.  That etch accomplished something
else that was very beneficial.  It got rid of the loosely attached bits of
silicon oxide that were mechanically trapped in the surface.  As the
crystals were used in the field the vibration dislodged that material,
which reduced the mass and caused the frequency to rise out of spec.
Bliley was forced by the govt to surrender their Intellectual Property to
other makers.

I have done a lot of surplus crystal etching using a buffered HF solution
(don't use straight HF for God's sake).  If folks are interested I could
write down my learnings.  I will share now that a quick dip in the solution
will "clean" a blank far better than alcohol can because the aforementioned
silicon oxide fragments clinging to the surface are easily removed by the
etch while the well ordered crystal structure is resistant to the etch and
doesn't reduce during the dip.  The freq typically goes up 100Hz as the
mass is removed.  Q improves as well.

Dennis AE6C
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