On 12/04/2020 03:46 PM, Rob Kossler via USRP-users wrote:
Hi Ofer,
Here is my understanding
- The E310 can sync to a PPS signal (either external input or obtained
from GPS). From this PPS, the E310 derives the 10MHz ref signal and
uses that as ref for LO signal. So, there will be lots of phase
variation between the LOs in all of your E310 devices even though they
will all be trying to stay in sync with a 1 pulse-per-second signal.
Basically, the E310 implements a "poor man's GPSDO" with the built-in
GPS module it has. It's the same algorithm as is used in the
B205mini series for the sync input. The control algorithm isn't
that good, and you cannot maintain coherence among multiple E310s
using this.
- Regarding your time synchronization question, there are examples of
setting the E310 clock (using set_time_next_pps, I think) to match the
GPS clock. Thus, all of your E310s could have the same time. But,
how do you plan to control all of your E310s when you want the
transmit to turn on? Will you have an SSH session to each of them?
Rob
Once all your E310 radio system clocks agree on time, you can used timed
streaming.
The "sync_to_gps" example application should give some broad help in
setting up GPS synchronization.
On Fri, Dec 4, 2020 at 2:28 PM Ofer Saferman via USRP-users
<usrp-users@lists.ettus.com <mailto:usrp-users@lists.ettus.com>> wrote:
Hello,
I would like to synchronize several E310 devices.
It is my understanding that the only way to do that is by
connecting a GPS antenna and performing disciplining to a derived
1-PPS signal.
I have a few questions to help me better understand how to make it
work:
1. Does GPS disciplining achieve frequency lock between devices or
phase lock?
2. How to start transmitting at the exact moment on all
synchronized devices? Can the unit clock be synchronized to GPS
clock? and then just start the transmission with some delay from
unit clock on all devices? Can someone share the relevant C
commands to perform the time synchronization to GPS clock or point
to a relevant code example?
Thanks,
Ofer Saferman
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