[USRP-users] usrp b210 and mimo

Marcus D. Leech mleech at ripnet.com
Fri Dec 5 10:58:31 EST 2014


On 12/05/2014 10:53 AM, Juha Vierinen wrote:
> Starttime is just a unix second about 10 seconds into the future.
>
> PPS is TTL from fanout buffer. I think the 10 MHz is +10 dBm. This is 
> the device: http://www.fei-zyfer.com/cs2.htm
>
> The same clock source works well with the N200. The B210 is kind of 
> synchronized, but there is ~100 microseconds of random offset between 
> restarts.
>
> juha
OK, and how are you measuring those offsets?  Sample timestamps against 
outside-world events?

>
> On Fri, Dec 5, 2014 at 3:22 PM, Marcus D. Leech via USRP-users 
> <usrp-users at lists.ettus.com <mailto:usrp-users at lists.ettus.com>> wrote:
>
>     On 12/05/2014 08:50 AM, Juha Vierinen via USRP-users wrote:
>>     I've slowly gathered the courage to try out the B210 devices. I
>>     was impressed by the fact that I could get 50 MHz of bandwidth
>>     out of it. However, I immediately ran into problems with absolute
>>     timing.
>>
>>     I've been using the B210 for mimo with USRP N200 devices for
>>     testing. The N200 devices all nicely synchronize themselves to
>>     the external PPS and after multiple restarts, their timing will
>>     be accurate. However, the starting time of the B210 seems to have
>>     a random component with a standard deviation of about 100
>>     microseconds. Every time I restart sampling, the offset between
>>     the N200 and the B210 is slightly different. There is no change
>>     in the timing offset between the N200 devices.
>>
>>     Is this a known issue, or am I doing something wrong?
>>
>>     This is how I configure the devices:
>>
>>     u.set_clock_source("external")
>>     u.set_time_source("external")
>>     tt = time.time()
>>     while tt-math.floor(tt) < 0.2 or tt-math.floor(tt) > 0.3:
>>         tt = time.time()
>>         time.sleep(0.01)
>>     print("Latching at "+str(tt))
>>     u.set_time_unknown_pps(uhd.time_spec(math.ceil(tt)+1.0))
>>     time.sleep(1)
>>     u.set_start_time(uhd.time_spec( starttime ) )
>>
>>     juha
>>
>>
>>     _______________________________________________
>>     USRP-users mailing list
>>     USRP-users at lists.ettus.com  <mailto:USRP-users at lists.ettus.com>
>>     http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
>     Where and how does 'starttime' get set?
>
>     How are you distributing your 1PPS and 10Mhz clocks?
>
>
>     -- 
>     Marcus Leech
>     Principal Investigator
>     Shirleys Bay Radio Astronomy Consortium
>     http://www.sbrac.org
>
>
>     _______________________________________________
>     USRP-users mailing list
>     USRP-users at lists.ettus.com <mailto:USRP-users at lists.ettus.com>
>     http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
>
>


-- 
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.ettus.com/pipermail/usrp-users_lists.ettus.com/attachments/20141205/3c5744d4/attachment-0002.html>


More information about the USRP-users mailing list