[time-nuts] CSAC Project(was CSAC purchase)

Bob kb8tq kb8tq at n1k.org
Wed Jan 24 17:19:07 EST 2018


The CSAC spec sheet calls out an aging rate of 0.9 ppb per month as 
“typical”. There is also a temperature spec of 0.4 ppb. If both are correct 
for your sample (*and* aging is linear ) you would be out by roughly 10 ppb
per year. There also is a voltage stability spec that might be impacted depending
on how you manage power. 

Taking the 30 ppb = 1 second number, you are at a 1 second / year rate after 3 years. 
At that point, you have already drifted by a second, if the assumptions are correct. 
This makes a massive assumption that the aging stays at the “typical” rate
for years. It’s a very good guess that it does not. Is it going to be 1/3 or 1/10
of typical over that period? Who knows. 

Bottom line, you are going to be pretty far from 1 second per 100 years with 
a CSAC based wrist watch, if it runs for years (or even for months).  It *will*
do *way* better than a TCXO or OCXO based watch over months or years.
It’s still not perfect. 


> On Jan 24, 2018, at 3:59 PM, Ronald Held <ronaldheld at gmail.com> wrote:
> Jim:
>  One around 1s/y, one 6 s/y and one 11 s/y. I was looking to do
> better than 1 s/100 years, but that was for the CSAC.
>          Ronald
> 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)
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