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Discussion and technical support related to USRP, UHD, RFNoC

IQ Imbalance calibration files

kunal sankhe

Wed, May 23, 2018 2:46 PM

Hi,

Using uhd_cal_tx_iq_balance and uhd_cal_rx_iq_balance, I am able to
find the coefficients of IQ Imbalance. However, I am having difficulty in
interpreting these results.

In calibration file, at lo_frequency=915MHz, correction_real=-0.00548
and correction_imag=0.00960. How can I estimate gain error and phase error
from these coefficients as described in the Wikipedia of IQ Imbalance
https://en.wikipedia.org/wiki/IQ_imbalance?

What are the last two columns 'measured' and 'delta' mean?

Now, as mentioned in https://files.ettus.com/manual/page_calibration.html,
we can ignore calibration files. However, how to use this feature in USRP
Source/Sink block in GRC?
When we run GRC file with USRP sink/source blocks, does USRP perform
calibrations every time or use values stored in calibration file stored in
/.uhd/cal/?

Thanks,
Kunal

Hi, Using *uhd_cal_tx_iq_balance* and *uhd_cal_rx_iq_balance*, I am able to find the coefficients of IQ Imbalance. However, I am having difficulty in interpreting these results. 1) In calibration file, at lo_frequency=915MHz, correction_real=-0.00548 and correction_imag=0.00960. How can I estimate gain error and phase error from these coefficients as described in the Wikipedia of IQ Imbalance https://en.wikipedia.org/wiki/IQ_imbalance? What are the last two columns '*measured*' and '*delta*' mean? 2) Now, as mentioned in https://files.ettus.com/manual/page_calibration.html, we can ignore calibration files. However, how to use this feature in USRP Source/Sink block in GRC? 3) When we run GRC file with USRP sink/source blocks, does USRP perform calibrations every time or use values stored in calibration file stored in /.uhd/cal/? Thanks, Kunal

Marcus D. Leech

Wed, May 23, 2018 4:55 PM

On 05/23/2018 10:46 AM, kunal sankhe via USRP-users wrote:

Hi,

Using uhd_cal_tx_iq_balance and uhd_cal_rx_iq_balance, I am able
to find the coefficients of IQ Imbalance. However, I am having
difficulty in interpreting these results.

In calibration file, at lo_frequency=915MHz,
correction_real=-0.00548 and correction_imag=0.00960. How can I
estimate gain error and phase error from these coefficients
as described in the Wikipedia of IQ Imbalance
https://en.wikipedia.org/wiki/IQ_imbalance?

What are the last two columns 'measured' and 'delta' mean?

Now, as mentioned in
https://files.ettus.com/manual/page_calibration.html, we can ignore
calibration files. However, how to use this feature in USRP
Source/Sink block in GRC?

It's automatic. If you look in the "FE corrections" tab in a UHD
source/sink, you can control whether the corrections are applied. The
default is that they
are applied.

When we run GRC file with USRP sink/source blocks, does USRP
perform calibrations every time or use values stored in calibration
file stored in /.uhd/cal/?

The corrections are applied from the stored calibration files--which
were previously produced with the cal_ utilities.

On 05/23/2018 10:46 AM, kunal sankhe via USRP-users wrote: > Hi, > > Using *uhd_cal_tx_iq_balance* and *uhd_cal_rx_iq_balance*, I am able > to find the coefficients of IQ Imbalance. However, I am having > difficulty in interpreting these results. > > 1) In calibration file, at lo_frequency=915MHz, > correction_real=-0.00548 and correction_imag=0.00960. How can I > estimate gain error and phase error from these coefficients > as described in the Wikipedia of IQ Imbalance > https://en.wikipedia.org/wiki/IQ_imbalance? > > What are the last two columns '*measured*' and '*delta*' mean? > > 2) Now, as mentioned in > https://files.ettus.com/manual/page_calibration.html, we can ignore > calibration files. However, how to use this feature in USRP > Source/Sink block in GRC? It's automatic. If you look in the "FE corrections" tab in a UHD source/sink, you can control whether the corrections are applied. The default is that they are applied. > > 3) When we run GRC file with USRP sink/source blocks, does USRP > perform calibrations every time or use values stored in calibration > file stored in /.uhd/cal/? > The corrections are applied from the stored calibration files--which were previously produced with the cal_ utilities.