Hi Michael, I don't have any ideas for reducing a time delay offset. But, I still wonder if the problem could actually be just a phase offset.
With a relative delay of 2.5ns and a bandwidth of 4 MHz, the amount of phase variation you would see is 0.57 degrees. That is not easy to see. On the other hand, if your bandwidth increased to 200 MHz, you would see phase variation of 28.6 degrees (if the delay offset is 2.5 ns). Rob On Tue, Jun 6, 2023 at 9:38 PM Michael Toussaint <mtoussa...@chaosinc.com> wrote: > Hi Rob, > > The signal is actually sweeping over 4MHz, but is just super zoomed into a > small piece to show the time delta so it looks CW. The time difference > appears to be the same (within my ability to measure) across the band so I > am assuming it is a time delay offset. > > Any suggestions on how to reduce this time delay offset? > > Thanks, > > Michael Toussaint > > > On Mon, Jun 5, 2023 at 8:51 PM Rob Kossler <rkoss...@nd.edu> wrote: > >> Hi Michael, >> Either a delay offset OR a phase offset will show itself as a relative >> phase. In order to distinguish between a delay offset and a phase offset, >> your signal must have appreciable bandwidth. It appears that your signal >> is CW. It is entirely possible that your delay offset is zero. Does this >> make sense? >> Rob >> >> On Mon, Jun 5, 2023 at 5:32 PM Michael Toussaint <mtoussa...@chaosinc.com> >> wrote: >> >>> Could you share how you're setting up LO sharing in your code, as well >>> as how you're setting the system clock on the N321? >>> >>> The functions "configure_channels" and "set_lo_hw_exports" are used to >>> set up the LO sharing. >>> >>> The functions "sync_sources" and "sync_all_devices" are used to set up >>> the system clock on the N321. >>> >>> How do you measure the relative delay? >>> >>> We are measuring the offset of the LO's by just measuring the phase >>> difference of the RF coming out of the Ettus with an Oscilloscope (picture >>> attached as >>> Scope_Trace_SingleStream_LO.png >>> >>> <https://mail.google.com/mail/u/0?ui=2&ik=34abf4583b&attid=0.1&permmsgid=msg-a:r-1207093291428225864&view=att&disp=safe&realattid=f_lijcykt50>). >>> Yellow is Channel 1, Green is Channel 2; using a single streamer we still >>> appear to have a 2.64ns delta or ~135 degree phase shift. >>> >>> Thanks Marcus and Rob for your assistance. >>> >>> Michael Toussaint >>> >>> def sync_sources(usrp): >>> logging.info('Setting Sync Sources') >>> >>> usrp.set_sync_source(clock_source = 'gpsdo', >>> time_source = 'gpsdo') >>> >>> def sync_all_devices(hw_info): >>> logging.info('Syncing All Devices') >>> >>> mb_with_gps_locked = -1 >>> >>> while 1: >>> time.sleep(1.0) >>> >>> all_ref_locked = True >>> >>> for board in range(hw_info.usrp.get_num_mboards()): >>> all_ref_locked = all_ref_locked and \ >>> hw_info.usrp.get_mboard_sensor('ref_locked', >>> board).to_bool() >>> >>> if (mb_with_gps_locked == -1) and \ >>> hw_info.usrp.get_mboard_sensor('gps_locked', >>> board).to_bool(): >>> mb_with_gps_locked = board >>> >>> if all_ref_locked: >>> logging.info('All Devices are REF locked') >>> break >>> >>> logging.info('GPS Locked on MB #%d', mb_with_gps_locked) >>> >>> time.sleep(1.0) >>> hw_info.usrp.set_time_next_pps( >>> uhd.types.TimeSpec( >>> hw_info.usrp.get_mboard_sensor('gps_time', >>> mb_with_gps_locked).to_int() + >>> 1.0) >>> ) >>> time.sleep(1.0) >>> >>> >>> def configure_channels(usrp, rf_type, hw_info): >>> rf_channel_index = None >>> set_rf_rate = None >>> set_rf_freq = None >>> set_rf_gain = None >>> set_rf_lo_source = None >>> get_rf_lo_source = None >>> get_rf_lo_freq = None >>> get_rf_lo_freq_range = None >>> >>> if (rf_type == 'rx'): >>> if (len(hw_info.rx_channel_index) > 0): >>> rf_channel_index = hw_info.rx_channel_index >>> set_rf_rate = usrp.set_rx_rate >>> set_rf_freq = usrp.set_rx_freq >>> set_rf_gain = usrp.set_rx_gain >>> set_rf_lo_source = usrp.set_rx_lo_source >>> get_rf_lo_source = usrp.get_rx_lo_source >>> get_rf_lo_freq = usrp.get_rx_lo_freq >>> get_rf_lo_freq_range = usrp.get_rx_lo_freq_range >>> else: >>> return >>> elif (rf_type == 'tx'): >>> if (len(hw_info.tx_channel_index) > 0): >>> rf_channel_index = hw_info.tx_channel_index >>> set_rf_rate = usrp.set_tx_rate >>> set_rf_freq = usrp.set_tx_freq >>> set_rf_gain = usrp.set_tx_gain >>> set_rf_lo_source = usrp.set_tx_lo_source >>> get_rf_lo_source = usrp.get_tx_lo_source >>> get_rf_lo_freq = usrp.get_tx_lo_freq >>> get_rf_lo_freq_range = usrp.get_tx_lo_freq_range >>> else: >>> return >>> >>> logging.info('Configuring %s Channels', rf_type.upper()) >>> >>> for rf_ch_name, rf_ch_index in rf_channel_index.items(): >>> logging.info('Configuring %s channel %s (channel #%d)', >>> rf_type.upper(), rf_ch_name, rf_ch_index) >>> >>> ch_def = hw_info.channel_def[rf_ch_name] >>> >>> # LO Channel Setup >>> current_lo_name = 'unknown' >>> current_lo_src = 'unknown' >>> >>> if ch_def.lo_inputs is not None: >>> logging.info(' Setting %s LO for Channel %s (#%d)', >>> rf_type.upper(), rf_ch_name, rf_ch_index) >>> >>> set_rf_lo_source(ch_def.lo_inputs.source, >>> ch_def.lo_inputs.name, >>> rf_ch_index) >>> current_lo_name = ch_def.lo_inputs.name >>> >>> logging.info(' (#%d) Requested %s LO name %s, src %s', >>> rf_ch_index, >>> rf_type.upper(), >>> ch_def.lo_inputs.name, >>> ch_def.lo_inputs.source) >>> else: >>> logging.info(' No %s LO inputs for Channel %s (#%d)', >>> rf_type.upper(), rf_ch_name, rf_ch_index) >>> >>> current_lo_name = 'lo1' >>> >>> current_lo_src = get_rf_lo_source(current_lo_name, >>> rf_ch_index) >>> >>> logging.info(' (#%d) Current %s LO name %s, src %s', >>> rf_ch_index, >>> rf_type.upper(), >>> current_lo_name, >>> current_lo_src) >>> >>> rf_lo_freq = get_rf_lo_freq(current_lo_name, >>> rf_ch_index) >>> >>> logging.info(' (#%d) [%s] Current %s LO freq %d', >>> rf_ch_index, >>> current_lo_name, >>> rf_type.upper(), >>> rf_lo_freq) >>> >>> rf_lo_freq_range = get_rf_lo_freq_range( >>> current_lo_name, rf_ch_index) >>> >>> temp = ' (#%d) [%s] Current %s LO freq range' + \ >>> ' [%d, %d] step %d' >>> >>> logging.info(temp, >>> rf_ch_index, >>> current_lo_name, >>> rf_type.upper(), >>> rf_lo_freq_range.start(), >>> rf_lo_freq_range.stop(), >>> rf_lo_freq_range.step()) >>> >>> logging.info(' Setting Sampling Rate %s', hw_info.fs) >>> set_rf_rate(hw_info.fs, rf_ch_index) >>> >>> logging.info(' Setting Center Freq %s', hw_info.fc) >>> tr = set_rf_freq(uhd.libpyuhd.types.tune_request(hw_info.fc), >>> rf_ch_index) >>> >>> logging.info(' (#%d) %s Tune Result:', >>> rf_ch_index, rf_type.upper()) >>> log_tune_result(tr) >>> >>> logging.info(' Setting %s Gain: %2.3f db', >>> rf_type.upper(), >>> ch_def.gain) >>> set_rf_gain(ch_def.gain, rf_ch_index) >>> >>> def set_lo_hw_exports(usrp, node_name, dirx, lo_enabled, output_array): >>> """Set LO HW Exports""" >>> if (lo_enabled is None) or (output_array is None): >>> return >>> >>> logging.info('Setting %s LO Export Enabled for %s', >>> dirx.upper(), node_name) >>> >>> if dirx.lower() == 'rx': >>> usrp.set_rx_lo_export_enabled(lo_enabled, 'lo1', 0) >>> enable_val = usrp.get_rx_lo_export_enabled('lo1') >>> elif dirx.lower() == 'tx': >>> usrp.set_tx_lo_export_enabled(lo_enabled, 'lo1', 0) >>> enable_val = usrp.get_tx_lo_export_enabled('lo1') >>> else: >>> logging.warning('Invalid direction %s', dirx) >>> return >>> >>> logging.info(' %s LO Export Enabled = %s, requested %s', >>> dirx.upper(), enable_val, lo_enabled) >>> >>> temp_path = 'blocks/0/Radio#0/dboard/' + \ >>> f'{dirx.lower()}_frontends/' + \ >>> '0/los/lo1/lo_distribution/LO_OUT_{}/export' >>> >>> logging.info('Setting %s LO HW Outputs for %s', >>> dirx.upper(), node_name) >>> >>> for out_num in range(len(output_array)): >>> hw_lo_export_path = temp_path.format(out_num) >>> >>> if usrp.get_tree().exists(hw_lo_export_path): >>> usrp.get_tree().access_bool(hw_lo_export_path).set( >>> output_array[out_num]) >>> >>> logging.info(' %s LO HW Export Out[%d] = %s, %s %s', >>> dirx.upper(), out_num, >>> usrp.get_tree().access_bool( >>> hw_lo_export_path).get(), >>> 'requested', >>> output_array[out_num]) >>> else: >>> logging.warning(' %s LO HW Export Out[%d] does not exist', >>> dirx.upper(), out_num) >>> >>> >>> On Thu, May 25, 2023 at 6:45 AM Rob Kossler <rkoss...@nd.edu> wrote: >>> >>>> On Thu, May 25, 2023 at 3:54 AM Michael Toussaint >>>> <mtoussa...@chaosinc.com> wrote: >>>> > >>>> > Used a single streamer and saw the delay slightly improve to between >>>> 2.5 - 3 ns. >>>> > >>>> > Any other suggestions to improve the delay to match the results from >>>> the knowledge base, https://kb.ettus.com/USRP_N320/N321_LO_Distribution >>>> ? >>>> >>>> How do you measure the relative delay? >>>> >>> >>> >>> >
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