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
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