[time-nuts] RE CSAC Project(was CSAC purchase)
jimlux at earthlink.net
Tue Jan 23 19:25:24 EST 2018
On 1/23/18 12:36 PM, Ronald Held wrote:
> What is you idea of portable in terms of size and mass for RbXO?
> I suppose I am try to do "better' and my TCXO watches which at best
> run around a second/year.
1 second/year is quite good - about 30 ppb. It's a bit tricky (like all
things time-nutty) - the "aging" on a TCXO could be that good - but the
instantaneous frequency control might not be that good. 1ppm is pretty
vanilla for a TCXO over a fairly wide temperature range, so 30 ppb at
"constant skin temp" (say, 5 C range) is probably reasonable.
I've got some test data here for some fancy TCXOs intended for space
with a spec of 2ppm aging first year and then 1ppm/year after that. The
actual aging in the first year was 0.08 ppm, at 70C. Some of the other
oscillators in the lot were 0.02ppm, 0.05ppm.
So, I think the spec here is "covers all the things that can go wrong",
but by cherry picking, you could do better.
(or, our system design could tolerate several ppm aging over years, and
"run of the mill" for Vectron was actually a lot better)
> OCXO and TCXO are both available smaller than the CSAC (particularly
> tcxo). I'm using a vectron EX-421 OCXO and it's about 1cm on a side,
> the OX205 is about 1" square and maybe 0.60" tall.
> TCXOs are available in "cellphone" form factors (e.g. tiny SMT packages)
> Long term, maybe a year, sounds like a reasonable goal. Maybe I am
> just chasing the next zero, if I have the metaphor correct?
> I’m guessing there was a question to me that somehow got lost in the world of
> ones and zeros ….
> My comment was in terms of temperature stability. The CSAC has a temp stability
> specification of +/-4x10^-10 over -10 to +70C. There are TCXO’s that
> will get below
> 5x10^-9 over that range and use far less power. There are OCXO’s that will get
> to better temperature stability numbers over that range. Neither one
> will do the long
> term aging that a Rb will.
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