[USRP-users] RF sensor time stamp synchronization across long distances
Marcus D. Leech
mleech at ripnet.com
Mon Dec 1 18:25:24 EST 2014
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
> 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.
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
Here's a handy coax loss table:
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.
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Shirleys Bay Radio Astronomy Consortium
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