[time-nuts] Looking for datasheet for Oscilloquartz 8602

[Bob Camp]

Hi


On Jun 1, 2013, at 4:24 PM, Jim Lux <jimlux at earthlink.net> wrote:

> 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"

You see a lot of different ADEV plots. Some would suggest flat from 0.1 seconds out. The real world is rarely that simple ….

> 
> 
>> 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 temperature effects.

Well, I've certainly seen TCXO's spec'd and 100% tested for ADEV in the 50,000 pc / year quantities …

> 
> If you need 0.1 ppm accuracy over -50 to +60C, you probably aren't going to get it with a TCXO.

Again, a "that depends" sort of thing. There are several outfits that will sell you a 0.01 ppm TCXO over a 100 degree span. -50 is not normally paired up with +60C, so there isn't a lot out there for that exact range. Doing 0.05 is not unreasonable over that range.  

> 
> 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.

Temp range isn't the issue as much as the range plus the radiation hardness required.

Bob

> 
> 
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.