Hi Francois, yes, that seems rather high; but maybe you're seeing the effects of the DC offset removal filter. You can try to use use set_auto_dc_offset(False) to make that faster [1].
However, usrp_spectrum_sense is pretty old, and hence can't even make use of stream tags on the GNU Radio side and timed commands on the USRP side, so the lower boundary for delay is the two-way latency between host and device -- which can easily be in the order of tens of milliseconds. I'd personally recommend just going ahead and reimplementing this: * Use the USRP source as usual * use set_time_now (if you don't have a time/PPS source), set_start_time * issue two or three timed tuning commands right at the start (set_command_time, set_rx_freq, clear_command_time) * write a python block that waits for rx_time tags (which automatically get added by the USRP source nowadays) * that block would, upon detection of such a tag, issue "the next tune request in line" (set_command_time(rx_time+delay), set_rx_freq, clear_command_time) * that block would, after detection of such a tag, first discard a few samples and then calculate your metrics based on the following N samples Best regards, Marcus [1] https://gnuradio.org/doc/doxygen/classgr_1_1uhd_1_1usrp__source.html#adb62a194b0b0761c6a0b4c8c808a20b0 On 03.08.2015 11:11, Francois Quitin wrote: > > Hi all, > > > > I want to retune the frequency of my USRP in Python during runtime. I > understand from usrp_spectrum_sense.py that I can just retune the USRP > during runtime, and that I need to allow for some tune_delay to make > sure that the samples corresponding to the old center frequency are > discarded. > > > > Is there any way to get a good estimate of tune_delay value? I want to > keep this as short as possible… (btw I’m using a USRP-N210 with WBX > daughterboard) Some trial and error gave me values around 50ms, but > this seems rather high compared to what I’ve read online. > > > > Any hints are welcome! > > Thanks, > > Francois > > > > -- > > > > > > _______________________________________________ > Discuss-gnuradio mailing list > [email protected] > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
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