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Mar 23rd, 2012
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  1. ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  2. Align LOs in the front-end (SBX/WBX + N-Series)
  3. ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  4. Using timed commands, multiple frontends can be tuned at a specific time.
  5. This timed-tuning ensures that the phase offsets between VCO/PLL chains
  6. will remain constant after each re-tune. See notes below:
  7.  
  8. * There is a random phase offset between any two frontends
  9. * This phase offset is different for different LO frequencies
  10. * This phase offset remains constant after retuning
  11.  
  12. * Due to divider, WBX phase offset will be randomly +/- 180 deg after re-tune
  13.  
  14. * This phase offset will drift over time due to thermal and other characteristics
  15. * Periodic calibration will be necessary for phase-coherent applications
  16.  
  17. Code snippet example, tuning with timed commands:
  18. ::
  19.  
  20. //we will tune the frontends in 100ms from now
  21. uhd::time_spec_t cmd_time = usrp->get_time_now() + uhd::time_spec_t(0.1);
  22.  
  23. //sets command time on all devices
  24. //the next commands are all timed
  25. usrp->set_command_time(cmd_time);
  26.  
  27. //tune channel 0 and channel 1
  28. usrp->set_rx_freq(1.03e9, 0/*ch0*/);
  29. usrp->set_rx_freq(1.03e9, 1/*ch1*/);
  30.  
  31. //end timed commands
  32. usrp->set_clear_time();
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