Dave wrote:
I found this new inexpensive GPSDO on ebay listed from a seller from China:
It looks interesting and tempting BUT.... the seller doesn't give
any spec's on the unit or osc type. The seller has 10 negative and
18 neutral feedback's in the past 6 months out of a total of 2110
for a feedback score of 99.6%; many for poor communication.
Does anyone on the list have any experience with this GPSDO? Any
advice on buying one?
The photo looks like the whole main board was soldered by hand rather
than by reflow. So, they appear to be onsie-twosies, not
manufactured products. The probability of assembly errors goes way
up for hand-assembled items.
As Dan already pointed out, it uses a recycled Morion OCXO, and the
failure rate of surplus Morion OCXOs is quite high. There is also no
information about the PLL loop, and with a DIY circuit the
presumption always has to be that it is not well designed (until the
presumption is rebutted by measurement data -- and in this case,
there is none).
Finally, because of the way that ebay seller ratings work in
practice, anything below 99.9% is a RISKY feedback score,
IMO. Particularly if something is coming from so far away that it is
hard or costly to return, I wouldn't buy from a vendor with a 99.6%
feedback score.
Could it be that the seller carefully QC's the Morions and they are
all good? Could it be that he knows how to design a good long-TC
all-digital PLL? Yes, both are possible. But until someone
independent and with stature and a track record in such matters (tvb,
Ackermann, and/or Miles) tests a few and posts the results, the
presumption is against both propositions.
Best regards,
Charles
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