Don Bowey wrote:
On 2/15/08 10:26 AM, in article ,
"Jeffrey D Angus" wrote:

John Byrns ) writes:
I'm still wondering why these are in tube type cases. It almost suggest
they are better than average crystals, and makes me wonder if they actually
have some sort of heater built in.

They're just a bit better than the tall HC/6-U crystal holder. And less
prone to enviromental issues than the FT-243 type holders.

The "tube" versions usually don't have a heater built in.

So the question is, what are these good for, can they be converted into
a useful project of any sort?

With the availability of crystal oscillator assemblies having better
than 10^-12 stability and and accuracy, there's not much you can use
one of these old crystals for.

A crystal oscillator will not achieve 10^-12 on its own. 10^-12 is the
stability of a Stratum II atomic clock.

Short term stability on a 6C4-based crystal oscillator is pretty good...
the phase noise is going to be lower than some PLL bench oscillators.

Long term stability... it's not very good... it's not good enough to pass
current FCC broadcast standards, even, without a really good oven. On
most of them you can see the frequency jump back and forth as the thermostat
opens and closes....
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

(Scott Dorsey) writes:

Short term stability on a 6C4-based crystal oscillator is pretty good...
the phase noise is going to be lower than some PLL bench oscillators.

Long term stability... it's not very good... it's not good enough to pass
current FCC broadcast standards, even, without a really good oven. On
most of them you can see the frequency jump back and forth as the thermostat
opens and closes....
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Proportional control, with modern parts will really help. My lab is
20C+/-3C, so getting 70C+/-1C should be pretty easy. Unfortunately,
that will still be pretty sloppy (about +/-1ppm). Just fine for
boatanchor calibrating and frequency spotting.

Steve.
--
Steven D. Swift, , http://www.novatech-instr.com
NOVATECH INSTRUMENTS, INC. P.O. Box 55997
206.301.8986, fax 206.363.4367 Seattle, Washington 98155 USA