misterious symetrical signal

[nexy_sm]

Hallo people,

During my adventure of designing 433MHz receiver i have recently discovered misterious simetrical signal which I am not able to explain to myself. I am using USRP1 with WBX daughter board. While observing complex baseband signal, I realized that depenting on RF gain I have a signal simmetrical to the transmitted signal. I have also attached a photo.

Hope that you have some explanation.

[Tom Rondeau-2]

On Tue, Nov 27, 2012 at 8:31 AM, nexy_sm <[hidden email]> wrote:

Hallo people,

During my adventure of designing 433MHz receiver i have recently discovered
misterious simetrical signal which I am not able to explain to myself. I am
using USRP1 with WBX daughter board. While observing complex baseband
signal, I realized that depenting on RF gain I have a signal simmetrical to
the transmitted signal. I have also attached a photo.

Hope that you have some explanation.

<http://gnuradio.4.n7.nabble.com/file/n38503/Screenshot.png>
<http://gnuradio.4.n7.nabble.com/file/n38503/Screenshot-1.png>

Looks like the effects of IQ imbalance.

I didn't read this closely, but this page looks like a pretty good explanation:

http://www.dsplog.com/2009/03/08/iq-imbalance-in-transmitter/

Tom

 

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[nexy_sm]

This looks pretty much like my problem.

I suppose that it is time for tuning?

by the way, can somebody remember the thread with very good GRC demonstrator of IQ imbalance and DC offset?

Nemanja

[nexy_sm]

I have USRP1 equipped with WBX and LFTX and LFRX daughter boards. When want to use uhd_cal_rx_iq_balance to calibrate my WBX board it won't do that, it says that calibration is not supported by hardware. I suppose the problem is uhd wants to calibrate LFRX board, and I don't know how to specify the oder board.
Any suggestions?

Regards
Nemanja

[nexy_sm]

Guys, any suggestions?

I got exactly this error:

[savi_ne@ts-070046nl ~]$ uhd_cal_rx_iq_balance --verbose
linux; GNU C++ version 4.4.6 20120305 (Red Hat 4.4.6-4); Boost_104100; UHD_003.004.003-221-g9d6f9492


Creating the usrp device with: ...
-- Opening a USRP1 device...
-- Loading FPGA image: /usr/local/share/uhd/images/usrp1_fpga.rbf... done
-- Using FPGA clock rate of 64.000000MHz...
Error: This board does not have the CAL antenna option, cannot self-calibrate.

Thanks again

[Josh Blum-3]

On 12/11/2012 03:32 AM, nexy_sm wrote:

> Guys, any suggestions?
>
> I got exactly this error:
>
> [savi_ne@ts-070046nl ~]$ uhd_cal_rx_iq_balance --verbose
> linux; GNU C++ version 4.4.6 20120305 (Red Hat 4.4.6-4); Boost_104100;
> UHD_003.004.003-221-g9d6f9492
>
>
> Creating the usrp device with: ...
> -- Opening a USRP1 device...
> -- Loading FPGA image: /usr/local/share/uhd/images/usrp1_fpga.rbf... done
> -- Using FPGA clock rate of 64.000000MHz...
> Error: This board does not have the CAL antenna option, cannot
> self-calibrate.

The utilities require transceiver boards like RFX, WBX, SBX. Also
unfortunately, requires FPGA support, which is not in USRP1.

-josh

>
> Thanks again
>
>
>
> --
> View this message in context: http://gnuradio.4.n7.nabble.com/misterious-symetrical-signal-tp38503p38623.html
> Sent from the GnuRadio mailing list archive at Nabble.com.
>
> _______________________________________________
> Discuss-gnuradio mailing list
> [hidden email]
> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
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[nexy_sm]

Hm, nothing like USRP1 is not supported is written here:
http://files.ettus.com/uhd_docs/manual/html/calibration.html
under the section of USRP1 it is even suggested to read.

But how to reduce IQ imbalance then?

On Tue, Dec 11, 2012 at 3:48 PM, Josh Blum-3 [via GnuRadio] <[hidden email]> wrote:

On 12/11/2012 03:32 AM, nexy_sm wrote:

> Guys, any suggestions?
>
> I got exactly this error:
>
> [savi_ne@ts-070046nl ~]$ uhd_cal_rx_iq_balance --verbose
> linux; GNU C++ version 4.4.6 20120305 (Red Hat 4.4.6-4); Boost_104100;
> UHD_003.004.003-221-g9d6f9492
>
>
> Creating the usrp device with: ...
> -- Opening a USRP1 device...
> -- Loading FPGA image: /usr/local/share/uhd/images/usrp1_fpga.rbf... done
> -- Using FPGA clock rate of 64.000000MHz...
> Error: This board does not have the CAL antenna option, cannot
> self-calibrate.

The utilities require transceiver boards like RFX, WBX, SBX. Also
unfortunately, requires FPGA support, which is not in USRP1.

-josh

>
> Thanks again
>
>
>
> --
> View this message in context: http://gnuradio.4.n7.nabble.com/misterious-symetrical-signal-tp38503p38623.html
> Sent from the GnuRadio mailing list archive at Nabble.com.
>
> _______________________________________________
> Discuss-gnuradio mailing list

> [hidden email]
> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>

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Nemanja Savić