[USRP-users] RF sensor time stamp synchronization across long distances

Marcus D. Leech mleech at ripnet.com
Fri Dec 5 16:23:26 EST 2014


On 12/05/2014 04:05 PM, Urban Hakansson wrote:
> I just wanted to follow up with a question. Could you tell me how many 
> dB loss the Octo-Clock G clock reference signals can experience and 
> the USRP B210 still be able to use the signal?
>
> Regards,
>
> Urban Hakansson
>
Refclock input to B210 should be in the range +10 to +15dBm
Similar for 1PPS.


> ------------------------------------------------------------------------
> *From: *"Marcus D. Leech" <mleech at ripnet.com>
> *To: *"Urban Hakansson" <uhakansson at tecore.com>, 
> usrp-users at lists.ettus.com
> *Sent: *Monday, December 1, 2014 6:25:24 PM
> *Subject: *Re: [USRP-users] RF sensor time stamp synchronization 
> across long distances
>
> On 12/01/2014 05:29 PM, Urban Hakansson via USRP-users wrote:
>
>     Hi everybody,
>
>     I am considering an application with multiple USRPs in an RF
>     sensor network, the sensors being located on the order of at least
>     100 feet apart.
>
>     I am thinking of a way of ensuring that at least the UHD packet
>     time stamps sent by each RF sensor over Ethernet to a central
>     server  for processing are synchronized to each other.
>
>     Would it be possible to just feed each USRP with a 1 PPS signal,
>     or do I need to feed the USRPs both the 10MHz and the 1 PPS
>     reference signals as a pair. Everything I have read indicates they
>     are both needed, but I just want to make sure.
>
>     Could I use the Octoclock G and run +100 feet of coax to multiple
>     URSP (RF sensors)? In other words how much attenuation could the
>     10MHz and the 1 PPS reference signals suffer due to path-loss
>     through extremely long runs of cable before becoming unusable?
>
>     Is there another and better way of synchronizing the UHD packet
>     time-stamps between RF sensors located far apart (one the order of
>     100 feet or more)?
>
>     Thanks for you consideration.
>
>     Regards,
>
> If you really want the clocks to be synchronized, you'll need common 
> 10MHz and 1PPS reference signals.  Without the common 10MHz, the units
>   will start out synchronized (using something like 
> set_time_unknown_pps()), but they'll drift apart, because they're each 
> using their own internal
>   clocks.
>
> Here's a handy coax loss table:
>
> http://www.w4rp.com/ref/coax.html
>
> If you're just looking at time-stamp synchronization, you could 
> install separate GPSDOs on each unit as well.  They won't agree on 
> fine-phase of the
>  10MHz signal, but they'll all agree "roughly" on 1PPS timing and 
> phase, so depending on your requirements, this might be adequate.
>
>
>     This e-mail may contain privileged, confidential, copyrighted or
>     other legally protected information, and is intended exclusively
>     for the intended recipient. If you are not the intended recipient
>     (even if the e-mail address above is yours), you may not review,
>     store, use, copy, disclose or retransmit it in any form. If you
>     are not the intended recipient or otherwise have received this by
>     mistake, please immediately notify the sender by return e-mail (or
>     sysadmin at tecore.com), then delete the message in its entirety.
>     Thank you.
>
>
>     _______________________________________________
>     USRP-users mailing list
>     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
>
>
> This e-mail may contain privileged, confidential, copyrighted or other 
> legally protected information, and is intended exclusively for the 
> intended recipient. If you are not the intended recipient (even if the 
> e-mail address above is yours), you may not review, store, use, copy, 
> disclose or retransmit it in any form. If you are not the intended 
> recipient or otherwise have received this by mistake, please 
> immediately notify the sender by return e-mail (or 
> sysadmin at tecore.com), then delete the message in its entirety. Thank you.


-- 
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/20141205/0e29467e/attachment-0002.html>


More information about the USRP-users mailing list