uhd

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Align LOs in the front-end (SBX/WBX + N-Series)

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Using timed commands, multiple frontends can be tuned at a specific time.

This timed-tuning ensures that the phase offsets between VCO/PLL chains

will remain constant after each re-tune. See notes below:

* There is a random phase offset between any two frontends

* This phase offset is different for different LO frequencies

* This phase offset remains constant after retuning

  * Due to divider, WBX phase offset will be randomly +/- 180 deg after re-tune

* This phase offset will drift over time due to thermal and other characteristics

* Periodic calibration will be necessary for phase-coherent applications

Code snippet example, tuning with timed commands:

::

    //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/*ch0*/);

    usrp->set_rx_freq(1.03e9, 1/*ch1*/);

    //end timed commands

    usrp->set_clear_time();

Align LOs in the front-end (others)