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| -rw-r--r-- | host/docs/sync.rst | 35 |
1 files changed, 34 insertions, 1 deletions
diff --git a/host/docs/sync.rst b/host/docs/sync.rst index 55c9f81f0..27eb345a7 100644 --- a/host/docs/sync.rst +++ b/host/docs/sync.rst @@ -152,8 +152,41 @@ For transmit, a burst is started when the user calls send(). The metadata should //send a single packet size_t num_tx_samps = tx_streamer->send(buffs, samps_to_send, md); +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ +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 +Align LOs in the front-end (others) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ After tuning the RF front-ends, each local oscillator may have a random phase offset due to the dividers |