[USRP-users] The problem with setting the frequency of USRP B 210.

Marcus D. Leech patchvonbraun at gmail.com
Tue Mar 12 09:12:24 EDT 2019


On 03/12/2019 05:13 AM, Ivan Zahartchuk via USRP-users wrote:
> Thanks for the information. But do not tell me why then in N 210 with 
> sbx there is no such problem? Just in the N 210 I am not satisfied 
> with the large central frequency. As I understand this is a surge in 
> direct current. But I can't get rid of him. And sometimes there are 
> problems with the mirror channel. If you have any advice on this, I 
> will be extremely grateful.
Because the SBX is a different piece of hardware, with different 
architecture.  It happens to tune a lot faster.

The DC offset can be dealt with using offset tuning:

https://files.ettus.com/manual/page_general.html

If you are seeing image frequencies, then use the

uhd_cal_rx_iq_balance

Utility on your N210 to caclulate and record calibration parameters that 
will help to reduce I/Q imbalance.  DC offset and I/Q imbalance are
   inherent in a direct-conversion receiver design.  These imbalances 
need to be calibrated out.  In the N210/SBX, host-side software does
   "static' measurement of these (using the above mentioned tooling) and 
records a calibrations file.  Those calibrations are then applied
   at run-time to compensate.

In the B210, the AD9361 chip does I/Q correction (and other corrections) 
dynamically, which can cause it to be slower in tuning--because it
   does the measurements whenever you re-tune.

See:

https://wiki.analog.com/resources/eval/user-guides/ad-fmcomms1-ebz/iq_correction

For a discussion

>
> пн, 11 мар. 2019 г. в 17:17, Ian Buckley <ianb at ionconcepts.com 
> <mailto:ianb at ionconcepts.com>>:
>
>     Ivan,
>     When the AD9361 is retuned, recalibration of various RF circuits
>     may (need to) reoccur. The device driver looks how far you have
>     retuned from a previous frequency, and if it exceeds a certain
>     distance rerun’s this calibration, which takes time.
>     Since Analog devices envisaged that this chip might need to be
>     used in applications where fast hopping is required, it does have
>     the ability to store multiple calibration settings locally in the
>     radio and switch between them quickly, but this is not
>     functionality that is used in basic operation under UHD. We may
>     well have put API hook’s in there so you can manually call this
>     functionality under UHD, but I can’t recall. Take a look at ADI’s
>     documentation for more info.
>
>     -Ian
>
>     > On Mar 11, 2019, at 7:49 AM, Ivan Zahartchuk via USRP-users
>     <usrp-users at lists.ettus.com <mailto:usrp-users at lists.ettus.com>>
>     wrote:
>     >
>     > Hello. I have a problem with the usrp b200 board. I need a fast
>     frequency tuning for spectrum analysis. But when I increase the
>     band over 200 MHz, that is, more than 8 frequency adjustments, I
>     have problems with time. It increases dramatically.
>     > Here is the code section where I measure the execution time of
>     the frequency setting function:
>     > for i, freqq in enumerate (freq):
>     >
>     >             recv_samps = 0
>     >             self.usrp.set_rx_rate (bandwich [i])
>     >             start = time.time ()
>     >             self.usrp.set_rx_freq (lib.types.tune_request (freqq))
>     >
>     >             print (time.time () - start)
>     > And I get the following results:
>     > 0.154153108597
>     > 0.00300002098083
>     > 0.0029628276825
>     > 0.00299215316772
>     > 0.00298380851746
>     > 0.153974056244
>     > 0.153841018677
>     > 0.00304222106934
>     > 0.00305104255676
>     > 0.0030951499939
>     > 0.0030038356781
>     > 0.153944015503
>     > 0.153861045837
>     > 0.00292587280273
>     > 0.00306510925293
>     > 0.00301003456116
>     > 0.0029399394989
>     > With USRP N 210 there is no such problem. Tell me why this
>     problem occurs and how can it be solved?
>     > Thanks in advance. Ivan
>     > _______________________________________________
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>
>
>
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