[time-nuts] New GPSDO on EBAY From China

Charles Steinmetz csteinmetz at yandex.com
Sun Dec 28 18:11:22 EST 2014

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,


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