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From: "Niels Rudberg J?rgensen" <niels.rudberg@post.tele.dk>
To: <rsgb_lf_group@blacksheep.org>
Date: Sun, 20 Aug 2006 19:18:15 +0200
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Subject: LF: re: modifying xtals etc.
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Hello LF-group.
About 50 years ago I ground and lapped FT243 crystals for use in lattice filters.
I would not recommend any attempts to try doing similar kinds of things to
modern crystls.
It may, however, be of interest to note, that the marked crystal frequency, e.g.
3.579,545 kHz is the oscillating frequency in a positive reactance oscillator
("parallel-type"). Operating the crystal at its series frequency will give you
a slightly lower frequency.
And if the crystal is being operated in its negative reactance region (beneath
its series resonance frequency, an even lower frequency of oscillation is
possible (down by up to 0.5 percent). A practical negative reactance oscillator
is one employing an inductance in series with the crystal. (Such oscillators 
sometimes are termed "VXOs"). As always, there is a price to pay:  The 
frequency stability is impaired. 
73
Niels / OZ8NJ+