Re: [Discuss-gnuradio] Synchronisation

[John Shields]

Thanks Derek,
                       No, I hadn't been power cycling between the runs - good point, obviously, I should have.

                       In terms of the 10 MHz and 1 pps references, in the configuration I was testing, I don't believe so in that I had the MIMO cable disconnected. My strategy was to have 2 USRPs with no MIMO - expecting little synchonisation. Then I was going to add the devices into the same container and connect the MIMO cable and expected things to improve and lastly, I was going to hand-code the SBX phase synch code.

                       In terms of the version of UHD, the fg shows: <<< Welcome to GNU Radio Companion 3.7.11.1 >>>

Thanks Marcus,
                       I will implement your way of measuring the running phase offset and also thanks for correcting my understanding of O/B GPS .


                       In terms of getting the devices in the container to be the best synch they can be, I presume for the device which has the GPS, for the clock source and time source, I would put O/B GPS for the device which has it and for the other, I would put MIMO cable for both but in terms of the 'Sync' field, where the options are PC Clock, Unknown PPS and Don't Sync, which option should I select?

                       Thanks again for your help.

                        Kind Regards,

                                 John


On 11/09/17 09:00, Derek Kozel wrote:

Hi John,

Are you power cycling the USRPs between tests or just rerunning the GRC flowgraph? Do you have shared 10 MHz and 1 PPS references? What version of UHD is printed in the output?

Thanks,

Derek

On Mon, Sep 11, 2017 at 1:50 AM, John Shields <address@hidden> wrote:

Thanks for the feedback but I am not sure that I understand it. What I was hoping to do was step through the configurations with increasing levels of synchronisation and expecting to see same.

Marcus' comment is correct and I have not, yet, put in the code which synchronises SBXs.

I guess my basic point, from looking at previous post from others Marcus L included, was that UHD would somehow improve the synchronisation between two USRPs in the same container versus those two separately.

When I executed the FG shown (separately) with the USRPs individually and then within a UHD container the results in terms of phase variation was the same. I had expected that, based on my understanding, the containerised USRPs would have behaved better.

So, either my FG does not measure what I thought it should or there is little UHD-related benefit to having USRPs individually or in the 'domain' as MarcusL has mentioned previously. From my situation it doesn't hence the first question in the post:


               Does my FG not measure what I claim to be wishing to measure?


Kind Regards,

            John

On 11/09/17 01:03, Marcus D. Leech wrote:

On 09/10/2017 08:58 PM, Dan CaJacob wrote:

I could be wrong, but I thought the SBX was one of the few daughter cards that starts with s known phase offset?

Only if you ask it to do so, and only if it's sharing clock with its buddies...

On Sun, Sep 10, 2017, 2:49 PM Fulcrum Associates <address@hidden> wrote:

Dear All,

              I have a couple of USRPs connected, through  a strong
attenuator to a signal generator (NWT4001). While the units have a MIMO
option, I don't have that cable. (Option A) When I run the GRC as
attached, I see too good a result to the extent that the differential
Phi seems to range over +/- 5 degrees.


              What I had hoped to prove to myself that two N200 with SBX
would have a varying offset without MIMO cable, then I would connect the
MIMO cable and move the USRPs into a multi-unit and enable GPSD O/B on
the unit which has the feature and MIMO for one without (Option B) and
that the phase differential would improve noticeably and be a variable
constant, but it didn't.


               If it had, but there still was a fixed phase offset which
varied each time it was setup (which is what I would expect under B)
then I would hand-code the SBX stream initialisation code to remove the
offset.


               Does my FG not measure what I claim to be wishing to
measure?

               If it does measure it correctly, why do my expectations
of options A and B leading to a different (though improved) situation
not eventuate?


               Kind Regards,


                              John

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Very Respectfully,

Dan CaJacob

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