I made a mistake buying the Micro Crystal unit, I thought it was going to be near enough spot on frequency like the Oscilloquartz one but better because it was new,
Still it will be usefull to have another to use as a reference.
I look for to see what the MC one is like and if it is stable.
I don't think that it was a mistake.
However it is clear from the specs that the Oscilloquartz is the better unit.
Turning to testing the Micro Crystal one....
Hooking it up initial current draw is 190mA, falling to 60mA as it warms up so that looks good and all in spec.
Leaving V
adj floating it settles at around 2.97V and, at that, the output is 21.27Hz high - so Flump's original measurement of 25Hz high was pretty close to mine. Certainly close enough for most of the difference to be explained by supply voltage differences (following measurements at V
DD = 5.002V), or ambient temp.
Pulling the V
adj pin to 1.974V gets it pretty close - 10.000000114MHz just now, but it's a pig to adjust by hand and is drifting somewhat making it almost impossible to pin down better than about 1 in 10
7.
Part of the reason it's harder to adjust is that the pull range of the MC unit is 10x the 8663 - ±3ppm (30Hz) rather than ±0.3ppm. This, in turn, is because the 10 year stability of the 8663 is 10x better than the MC one.
The 8663 also has a better rejection of supply variations as well: 3x10
-10 over the 12V ±5% supply voltage range vs 1x10
-7 for the MC oscillator. Running on the breadboard I'm finding it hard to pin down the last mV of stability on V
DD and V
adj and it definitely affects the MC unit more than the 8663.
the 8663 is also massively better on variation vs ambient temp. The spec is 4x10
-9 over the operating temperature range of -20
oC to +70
oC. The corresponding figure for the MC unit is 150x10
-9 even for the "high stability" variant.
At the end of the day this oscillator is probably in spec but playing with it mirrors the experience I had with another unit that I (coincidentally) bought off the same vendor - I just couldn't get it to settle down to much better than 10
-7 stability. Conversely another one I had (again from the same source) is much better behaved. I suspect the MC unit was designed assuming fairly tightly controlled supply voltage and probably the frequency control voltage coming from a DAC rather than a multi-turn trimpot.
I think that if Flump wants a reference oscillator the 8663 is by far his best choice - if he drives the frequency control pin at 4.75V it will almost certainly be within 0.1Hz of 10MHz. To reliably get any more accurate I think will take a Rubidium standard or GPSDO - sadly both now seem very rare on ebay. In fact even cheap OCXO's are not as cheap or plentiful as 12-18 months ago.