[USRP-users] N200 stability

Marcus D. Leech mleech at ripnet.com
Wed Apr 22 12:16:23 EDT 2015


On 04/17/2015 09:08 AM, Dan Sego via USRP-users wrote:
> Good morning the list.
>
> I have 2 N200s w/ WBX connected via MIMO cable with an internal GPSDO 
> on the master. I have attached calculated intra-channel and 
> inter-channel phase stability calculations on from a tone generator. 
> The results over approximately 100 seconds demonstrate about 0.15 
> radians of drift with a fair amount of low frequency noise. The low 
> frequency noise (1 Hz-ish) is common to both channels.
>
> Are these results consistent with expectations? I have also attached 
> the two channel code as I'm still not completely sure that I have 
> configured the clock correctly (and by coincidence just 
> seeing hanwen's posted query, in particular the option of GPSDO or? MIMO).
>
> Any and all advice is appreciated. Thanks
> Dan Sego
>
>
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I don't see anywhere in your code where you're setting the master-side 
clock source to "gpsdo" or "external"  -- also on the N210, those two are
   conceptually the same, with a hardware jumper selecting whether the 
"external" clock comes from the front-panel or the on-board GPSDO.

There's a jumper block on the mainboard, J510, which selects between the 
front-panel 10MHz in, or the 10MHz provided by the on-board GPSDO--make
   sure that's in the correct position, selecting connector J507 instead 
of J501.

How are you connecting the signal generator to the two N210s?  Is it 
conceivable that mutual phase-drift is a temperature effect of the way the
   signals are being distributed?


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