[time-nuts] New GPSDO on EBAY From China

Bob Camp kb8tq at n1k.org
Mon Dec 29 09:27:55 EST 2014


Ok, well that’s a move forward on this GPSDO. There is a *lot* more data on that listing than there was a month ago. 

Thanks for digging it up  and posting the link.

If you look at the ADEV at 1 second, it’s running at 2.67 x10^-11. That’s all coming from the Erratum Rb that they are using as a reference. At 100 seconds the Rb should be around 2.67 x10^-12 and the MV-89 should be about < 2x10^-11. They combine as the square root, so that would be 3.3 ppt or less. The unit is running at 4.8 ppt so the filter is having some impact at that point. 

Out around 5,000 seconds the unit has a major hump. The Nortel GPSTM has a similar hump, but much closer in. It’s performance at 5K seconds is much better. The Lucent KS boxes beat this part across the entire range. That makes some assumptions, since there is no good ADEV data inside 100 seconds on the plot.

The final question about the plot would be - what happens at longer tau? The run was stopped before it really got past the peak in the filter. It would be nice to see some data that at least gets back down to < 1 ppt at the longer tau’s. Without that data it’s unclear how well the whole system is doing. That’s not to say it’s not doing well. It could be doing a great job, there’s just no way to know from the data. 


My guess is that this is very much like your counter project, just a bit further along. They have a nice looking unit, but are still trying to figure out the bugs and finish up the software …


> On Dec 28, 2014, at 6:19 PM, Li Ang <lllaaa at gmail.com> wrote:
> Hi
>   This unit is done by BG7TBL. In his store on taobao.com, there is a adev
> chart. Please refrer to this link
> http://item.taobao.com/item.htm?spm=a1z10.3.w4002-1278071728.49.XHJlQL&id=42336500072
> 2014-12-29 1:56 GMT+08:00 Dan Rae <danrae at verizon.net>:
>> On 12/28/2014 7:25 AM, David Smith wrote:
>>> Hello Friends,
>>> I found this new inexpensive GPSDO on ebay listed from a seller from
>>> China:
>> Dave, these have been discussed in the past at some length on this list.
>> I would point out that they use a re-cycled Morion OCXO.  I have had two of
>> these ovens from China; one worked fine, the other has a very high level of
>> spurious outputs.  I would be wary of using these in anything without first
>> testing them thoroughly.
>> Dan
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