Text 93, 28 rader
Skriven 2004-11-02 23:41:04 av MIKE ROSS (1:167/133.0)
     Kommentar till en text av Greg Mayman
Ärende: STILL AROUND
====================
"Greg Mayman" bravely wrote to "Roy J. Tellason" (02 Nov 04  12:28:00)
 --- on the heady topic of "STILL AROUND"

 GM> The fact that the frequency is specified to six decimal places
 GM> makes me think that they may have some electronic temperature
 GM> compensation built in.

 GM> Many years ago I read about an oscillator circuit using an
 GM> NTC mounted close to the crystal to monitor the temperature, with
 GM> feedback to a varactor diode to compensate for the crystal's
 GM> natural thermal-versus-frequency variation.

 GM> That Saronix oscillator is marked NTC070C which could indicate a
 GM> negative temp coefficient of 70 ppm per degree C... or maybe
 GM> something quite different <G>

Crystals have various plane geometries along which they are cleaved or
cut. Since some planes have an NTC and some PTC, what a maker will often
do is to cut across these so that the resulting crystal is nearly NP0.
Also some cuts are parallel resonnance and others series resonnance but
one will see them used in TTL clocks quite indiscriminately. Crystal
making is a complex science and I don't pretend to know it well.

 M*i*k*e

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