[USRP-users] usrp b210 and mimo

Juha Vierinen x at mit.edu
Fri Dec 5 10:53:32 EST 2014


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

On Fri, Dec 5, 2014 at 3:22 PM, Marcus D. Leech via USRP-users <
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 listUSRP-users at lists.ettus.comhttp://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 Consortiumhttp://www.sbrac.org
>
>
> _______________________________________________
> USRP-users mailing list
> USRP-users at lists.ettus.com
> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
>
>
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