[time-nuts] Looking for datasheet for Oscilloquartz 8602

[Bob Camp]

Hi

On Jun 1, 2013, at 12:21 PM, Magnus Danielson <magnus at rubidium.dyndns.org> wrote:

> Attila,
> 
> On 06/01/2013 05:11 PM, Attila Kinali wrote:
>> On Wed, 29 May 2013 01:59:12 +0200
>> Magnus Danielson<magnus at rubidium.dyndns.org>  wrote:
>> 
>>> On 05/28/2013 07:55 PM, Attila Kinali wrote:
>>> 
>>> http://www.pttimeeting.org/archivemeetings/1984papers/Vol%2016_10.pdf
>>> 
>>> See also
>>> http://www.pttimeeting.org/archivemeetings/1979papers/Vol%2011_25.pdf
>> 
>> Interesting stuff. Thanks a lot!
>> 
>>>> Juup. I just went back to Vig's tutorial and read up what he wrote.
>>>> Misremembering things is not a good thing...
>>>> But then, he explicitly writes that SC cut gives a higher stability
>>>> over AT cut due to lower temperature dependence and less dips.
>>> 
>>> That is true, but your discreditation of AT-cut was simply way off the
>>> mark, so I wanted to bring it into context. There is a difference, but
>>> it is not as huge as it sounded like. I like to think about it as such
>>> that you better have done much of your homework in form of good
>>> oscillator and oven before considering spending money on going from
>>> AT-cut to SC-cut, but it does give that extra performance if you need
>>> it. The OSA 8600 shows just how far you can take AT-cut.
>> 
>> Oh.. Ok. Didn't want to sound that way. On the other hand, that conclusion
>> is not far from the truth. I still have a lot to learn. Thanks for the
>> correction.
> 
> The benefits (as I recall it) is a somewhat higher Q and less thermal dependence.

Actually on a direct "same sized blank / same frequency" basis, the Q of an AT is often higher than the Q of an SC. Because the SC is higher impedance, it's phase slope will be higher.

Bob

> 
>> But then, the 8600 has a ~10dB higher noise then the 8607. Ie the noise
>> is 10 times higher (it is power-dB, not voltage-dB isn't it?). Which
>> makes me wonder what the noise contribution is. I would assume that the
>> electronics are very similar if not the same (electronics are cheap compared
>> to the crystal) and the mechanical construction seems to be very similar
>> as well.
> 
> You must be looking at the 1 Hz numbers. You really need to look at the phasenoise at different offsets to understand what goes on.
> 
> The electronics contribute a white phase noise, as well as a flicker noise (1/f, a -10 dB/decade slope). The resonators Q-value and frequency will define the break-up point, below witch you have a -20 dB/decade slope and above it is flat. Depending on the resonator at hand, you then see a 1/f or 1/f² noise between the flat white noise and the 1/f³ noise. The output amp can then add white phase noise and flicker phase noise.
> 
> The 10 dB improvement I would attribute to the improved Q value with SC cut crystal, but... these are not the real values, it's the published values which is guaranteed for a product. Actual values is different.
> 
> Looking in Enrico Rubiolas book, he measures both OSA 8600 and OSA 8607 (among others) and then the actual numbers is much closer. The 1 Hz values is only 4 dB different, but then the wideband noise between these two samples lets the 8600 be 2 dB quieter than the 8607 at -155 vs. -153 dB.
> 
> So, we go back to actual measurements, we need to realize that each oscillator is unique, and that data-sheets only intends to give some form of guarantee of how bad they will be as they exit the factory, but not necessarily reflect all aspects of the oscillator.
> 
> I've seen AT-cut oscillators behave better than SC-cut within the same basic conditions, but where the AT-cut was much better implemented.
> 
> So, there is a difference, it's just not very large and the full performance depends on so many other parameters of a design. The cost of SC-cut blanks is higher, and it is not meaningful to use one unless the design have come so far that it starts to become a limiting factor and other improvements is more expensive.
> 
>> In comparison the stability between 2 and 30s has only a factor of 2 inbetween.
>> (maximum instability according to spec).
>> 
>> Any ideas what the reason could be?
> 
> #1 Datasheet specing difference.
> 
> #2 Actual difference is due to Q-value difference, moving the break-up point from the Q value.
> 
> So, the Leeson model explains this pretty well, and the difference in Q-value of the loaded crystal blank is then reflected in noise differences with essentially the same buffer electronics.
> 
> Cheers,
> Magnus
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