[USRP-users] Phase sync multiple x310s

Martin Braun martin.braun at ettus.com
Thu Jul 6 15:29:12 EDT 2017


If you have the option to use uhd_siggen_gui (it's a GNU Radio tool),
that should run through all the right steps to set up synced Tx. Then
you'd know if it's a SW issue.

-- M

On 05/19/2017 08:16 AM, Vladica Sark via USRP-users wrote:
> Hi Julian,
> 
> I am using Teledyne LeCroy HDO9404. I use UHD 3.10.1 which should be
> stable.
> 
> In my case, the signal on the scope also looks nice. Nevertheless, when
> I precisely estimate the phase between the separate channels there are
> these 45 degrees jumps. The phase offset itself is not a problem, if it
> is constant, since it can be corrected.
> 
> I would try this with the timed commands to see if it helps, but on Monday.
> 
> BR,
> Vladica
> 
> 
> On 19.05.2017 15:35, Julian Arnold wrote:
>> Hey Vladica,
>>
>>> I think that I need to add something like
>> I haven't looked at tx_waveforms but here is a snipped from my code:
>>
>> ###############################################
>>
>>      this->usrp->set_clock_source("external"); //applies to all mboards
>>      this->usrp->set_time_source("external"); //applies to all mboards
>>
>>      double tx_freq = 3.700010e9;
>>      double rx_freq = 3.700000e9;
>>
>>      //Set time at next PPS to zero
>>      this->usrp->set_time_unknown_pps(uhd::time_spec_t(0.0));
>>      boost::this_thread::sleep(boost::posix_time::seconds(3));
>>
>>      uhd::time_spec_t cmd_time = usrp->get_time_now() +
>>          uhd::time_spec_t(0.3);
>>
>>      //sets command time on all devices
>>      //the next commands are all timed
>>      this->usrp->set_command_time(cmd_time);
>>      this->usrp->set_tx_freq(tx_freq, 0);
>>      this->usrp->set_tx_freq(tx_freq, 1);
>>      this->usrp->set_tx_freq(tx_freq, 2);
>>      uhd::tune_result_t freq_is = this->usrp->set_tx_freq(tx_freq, 3);
>>          boost::this_thread::sleep(boost::posix_time::seconds(3));
>>      //end timed commands
>>      this->usrp->clear_command_time();
>>
>> ###############################################
>>
>> What scope are you using? I was observing phase stability across the 4
>> channel on an DSO90804A and found it to be basically rock solid and
>> clearly visible
>> (As long as the temperature was constant. This meant to wait for
>> something like 10-30min after startup for the devices to reach final
>> operating temperature).
>>
>> Also, which version of UHD are you running?
>>
>> Cheers,
>>
>> On 05/19/2017 03:09 PM, Vladica Sark via USRP-users wrote:
>>> Hi Julian,
>>>
>>> I think that I need to add something like
>>>
>>> //we will tune the frontends in 100ms from now
>>> uhd::time_spec_t cmd_time = usrp->get_time_now() +
>>> uhd::time_spec_t(0.1);
>>> //sets command time on all devices
>>> //the next commands are all timed
>>> usrp->set_command_time(cmd_time);
>>> //tune channel 0 and channel 1
>>> usrp->set_rx_freq(1.03e9, 0); // Channel 0
>>> usrp->set_rx_freq(1.03e9, 1); // Channel 1
>>> //end timed commands
>>> usrp->clear_command_time();
>>>
>>> in the tx_waveforms but for the transmitter.
>>> I would try this on Monday.
>>>
>>> Anyway, in my case also the phase looks quite stable on the scope. The
>>> 45 degree jumps cannot be easily noticed. I acquire the data and with
>>> post processing I come to these results.
>>>
>>> BR,
>>> Vladica
>>>
>>>
>>> On 19.05.2017 14:05, Julian Arnold wrote:
>>>> Hey Vladica,
>>>>
>>>> I recently ran the same experiment.
>>>> Once the LOs are properly locked to the reference, the time is
>>>> synced to
>>>> the reference and you have tune the boards using timed commands at the
>>>> same time,
>>>> you should be left with a pretty stable output across all 4 TX
>>>> channels.
>>>> There will, of course, be a fixed phase offset between the different
>>>> channels.
>>>> This offset will also depend on temperature.
>>>>
>>>> Let me know if you have questions regarding the software
>>>> implementation.
>>>>
>>>> Cheers,
>>>>
>>>> On 05/19/2017 01:50 PM, Vladica Sark via USRP-users wrote:
>>>>> Hi,
>>>>>
>>>>> I have two x310s with 2x UBX daughterboards in each. I bring 10MHz and
>>>>> 1 PPS from octoclock to the both of them. With tx_waveforms I transmit
>>>>> a CONST and record the resulting waveforms on a scope. The carrier is
>>>>> 2.45 GHz.
>>>>>
>>>>> The phase difference between the four available channels jumps for
>>>>> +-45 degrees randomly. Without these jumps, the phase difference would
>>>>> have probably been constant. This is the same for all of the channels.
>>>>>
>>>>> Is there a chance to phase sync the two x310s and the four
>>>>> transceivers?
>>>>>
>>>>> BR,
>>>>> Vladica
>>>>>
>>>>> _______________________________________________
>>>>> 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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>>
> 
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