[time-nuts] Looking for datasheet for Oscilloquartz 8602
jimlux at earthlink.net
Sat Jun 1 16:24:26 EDT 2013
On 6/1/13 10:35 AM, Bob Camp wrote:
> Both suffer from people talking about levels (-120 dbc or 1x10^-11) without mentioning the offset or tau. Since both are highly dependent on the offset or tau that's not a good thing. My observation is that ADEV is much more likely to be mentioned without an associated tau than phase noise without an offset . I've also observed that when the error is mentioned you are likely to get a "oops I'll fix that" on phase noise. On ADEV people often simply don't get the fact that tau matters even after it's pointed out.
For ADEV, a lot of oscillators have a sort of "floor" where the ADEV is
relatively constant, say from tau in the range10-1000 seconds, and then
it rises up (from thermal effects and such), so the shorthand is that
the number quoted is that "floor value"
> Looking at what the systems using OCXO's are actually doing, about half the time ADEV is probably the better / more important measure than phase noise. The system is more sensitive to the OCXO wandering around over 100 or 1000 seconds than it is on the level of a sideband offset how ever many Hz off carrier. Once you get past ADEV, you rarely see an OCXO specified for any of the other related specifications. That's a shame, since some of them are better measures of certain things than ADEV. Again, I blame the fact that people just don't understand / trust the measurements.
Certainly for "OC" applications this might be true. Although, a sort of
trend is that the TCXO resonator has to have a lower Q, so the
temperature compensating components can "pull" it to the right frequency
over temperature, so the phase noise of a TCXO isn't as good as that of
an OCXO, which can have a higher Q.
A lot of times, though, an OCXO is chosen because a TCXO doesn't have
frequency stability needed over environmental changes. I don't think
ADEV is really the right measure when you're looking at aging or
If you need 0.1 ppm accuracy over -50 to +60C, you probably aren't going
to get it with a TCXO.
For example, the Space Network using TDRSS on S-band (2.2 GHz) requires
you know the actual frequency to within 700Hz. That's 0.3 ppm and tough
to get in a TCXO over space qual temp range.
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