Misterious symetrical signal

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


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

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

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


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Guys, any suggestions?

I got exactly this error:

[[email protected] ~]$ 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


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

– 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

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


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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 B.-3 [via GnuRadio] <

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