GandalfG8 at aol.com
GandalfG8 at aol.com
Sat Oct 11 14:42:49 UTC 2008
In a message dated 11/10/2008 05:12:11 GMT Daylight Time, smace at intt.net
Has anyone "upgraded" the oscillator on an older Datum BC637PCI card to
the MTI crystal? Is it as simple as changing the crystal and adjusting the
I've not changed the oscillator, but I did look into the possibility and
also ran a BC637PCI for a while with an external Vectron ovened 10MHz oscillator.
I assume you have the BC637PCI manual?
Appendix A refers to field upgrades, both converting a 635 to 637 by adding
the GPS module and upgrading to the ovened oscillator.
In both instances a firmware "upgrade" was activated by entering a device
specific password provided by Datum/Symmetricom. I doubt that option is still
longer available even though the necessary firmware changes are obviously
already there waiting to be activated.
I suspect, in the case of the oscillator upgrade anyway, some default
settings including oscillator gain will be all that's changed.
When running with an external oscillator I found that loss of power would
default any settings I had changed so no doubt that's what would happen if you
upgraded the oscillator without the firmware change.
Page 6-15, in the rev K manual anyway, gives details of the oscillator gain
adjustment, I found approx 70 seemed reasonable with my Vectron oscillator
but my BC637PCI, and perhaps others, has some conditioning issues anyway.
The basic onboard oscillator was not very good, apologies for such an
imprecise statement but I can't find the fairly extensive notes made several months
ago, both accuracy and stability were relatively poor measured on an
HP53132A using a known good Thunderbolt as a reference.
In particular I noticed quite frequent, but seemingly random, jumps in
output frequency that would then take a little while to recover, a bit like a fast
acting automatic gain control with slow recovery time. These jumps were
significantly greater than the "normal" variations I observed and fell outside of
the unit specification.
Using the Vectron oscillator greatly improved things, it was a much better
oscillator anyway and I was able to observe the significant improvement in the
Vectron performance when being conditioned by the BC637PCI.
However, the frequency jumps still occured albeit with overall performance
much improved and frequency stability much better and the jumps less than
before, ie frequency jumps were seemingly reduced in proportion to the better
Without the jumps I would have been happy with the Vectron performance but
didn't feel able to trust the combination without permanent computer
monitoring, and still don't know if this was a function of my BC637PCI or something
common to all of them.
It was interesting to play with, and I'll probably go back to it at some
time, but I was more concerned then to set up something I could rely on and
eventually put it to one side.
Whilst working with the BC637PCI I did find that I needed both the BC635PCI
and BC637PCI software, both offer options the other lacks, and I have late
copies of both if you need them.
I also have two manuals, version H from Datum that includes schematics, and
the fairly similar version K from Symmetricom but without schematics.
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