[time-nuts] Looking for datasheet for Oscilloquartz 8602

Jim Lux jimlux at earthlink.net
Sat Jun 1 18:58:28 EDT 2013


On 6/1/13 1:46 PM, Bob Camp wrote:
> Hi
>
>> 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 ….
>


Yes.. but still, a floor of sorts.. high at the low end, high at the 
high end (for tau), and flattish in the middle.

>>
>>
>>
>> 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 …


Sure, but is ADEV *of the oscillator at constant temp* really relevant 
when your application isn't at constant temp.  I guess it is, because 
your system ADEV can't be any better than the underlying oscillator, but 
still, I'm not sure it's an entirely appropriate specification to be 
calling out.

And, isn't "aging" (in the sense of slow long term drift) usually 
excluded from the ADEV calculation (e.g. you fit a straight line to the 
raw frequency data, and subtract that out)




>
>>
>> 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.

0.05 ppm in a TCXO over 100 degrees as a "assembly" or "component" level 
device? That's quite impressive.  I see that Vectron has the TX402 which 
is 50 ppb -20 to +70 (for some frequencies, according to data sheet) 
which is certainly in that ballpark.


>
>>
>> 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.
>

LEO doesn't require much in the way of radiation hardness. After all, 
people live in LEO, so it can't be that bad.  Single event effects 
maybe.  Or frequency change with dose/single events.

Seeing the recent RAD data from MSL only racking up <100 rad on the way 
to Mars makes me wonder why we ask for 20kRad kinds of performances.


> Bob
>
>>
>>
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