[USRP-users] Calibrate tool not work

Page Jack jack.page999 at gmail.com
Sat Sep 14 20:53:21 EDT 2013


Hi Marcus,
thanks. Since you have successfully calibrated usrp I must my fpga source
wrong. I will try to debug my fpga source.


On Sun, Sep 15, 2013 at 1:22 AM, Marcus Müller <marcus at hostalia.de> wrote:

>  Hi Jack,
> sorry, I can't really make much sense of what you are telling us, so I
> reply what I understood.
>
> I do not use the loop version tool.
>
>  I did not understand that. "loop version tool" is what? and what are you
> using to calibrate?
>
>  I calibrate usrp1 and wbx board.
>
>  ok, understood, USRP 1 and WBX. Versions unknown/unreported.
>
>  since usrp1 do not provide calibrate ability
>
>  You think the USRP 1 is not able to calibrate itself.
> That is correct, but also true for USRP 2/N210 and every other USRP I know
> of.
> I/Q imbalance calibration is usually done completely in software on the
> host PC.
> That relies on signal that leaks from the TX chain into the RX chain, see
> http://files.ettus.com/uhd_docs/manual/html/calibration.html .
> So to calibrate right, you should _not_ plug in a spectrum analyzer
> _while_ calibrating.
>
>  I modify the fpga
> image
>
>
> So you modified the FPGA image. What did you do?
>
>   then I modify the calibrate tool let usrp output to a spectrum
> analyser.
>
>  The calibrate tool just uses the normal TX / RX interface but sets the
> antenna to "CAL", a special value that basically builds a loopback between
> TX and RX (if I read lib/usrp/dboard/db_wbx_simple.cpp correctly).
>
>  no matter what the value I set the output do not affected.
>
>  I can't understand: You set which values to what?
>
>  I
> wonder if anyone successfully calibrate usrp and the image signal be
> supressed.
>
>  I can't try it right now, but to be honest: Calibration worked for me in
> the past, and it suppresses the image spectrum reasonably well; I'd expect
> your image to be more than 40dB weaker than your desired signal.
> How high is the power of your image signal and how high the power of your
> desired signal? Can you upload a photo somewhere?
>
>   If so then it might be my modify have mistake.
>
>  So far I don't think you made a mistake :)
>
> Greetings,
> Marcus
>
>
>
> Regards
>
> On 9/12/13, Marcus Müller <marcus at hostalia.de> <marcus at hostalia.de> wrote:
>
>  Hi!
>
> Um... you can't actually see anything with an external spectrum analyser
> "during" calibration; calibration basically is based on leakage between
> TX on RX on the same daughterboard, if I remember correctly.
> After TX calibration, the image should be as good as gone. Since it is
> not affected, my wild guess is that it is not actually an image due to
> IQ imbalance.
> However, the information you provided is a little to sparse for me to
> take an educated guess. Supply us with
> - device type (USRP / daughterboard incl. version)
> - signal type
> - center frequency
> - amplitude difference (in dB preferably) between original and mirror
> spectrum
> - theorethic/measured (by absfft plot) spectrum of transmitted samples
>
> Greetings,
> Marcus
>
>
>  Hi,
> I want to calibrate usrp i q imbalance. I use calibrate tool in uhd,
> but the calibrate result is not right. I watch the spectrum analyzer
> to observe the image signal during calibrate. but the image signal do
> not affected by the calibrate tool.
>
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