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UHD - Calibration Application Notes
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.. contents:: Table of Contents

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Self-calibration
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The UHD comes with several self-calibration utilities for minimizing IQ imbalance and DC offset.
These utilities perform calibration sweeps using transmit leakage into the receive path
(special equipment is not required).
The results from a calibration are written to a csv file in the user's home directory.
UHD will automatically apply corrections at runtime when the user re-tunes the daughterboard LO.
Calibration results are specific to an individual RF board.

**Note:**
When a calibration table is present,
and the user wishes to override the calibration settings through the API:
the user should re-apply the desired setting every time the LO is re-tuned.

UHD comes with the following calibration utilities:

 * **uhd_cal_rx_iq_balance:** - mimimizes RX IQ imbalance vs LO frequency
 * **uhd_cal_tx_dc_offset:** - mimimizes TX DC offset vs LO frequency
 * **uhd_cal_tx_iq_balance:** - mimimizes TX IQ imbalance vs LO frequency


The following RF frontends are supported by the self-calibration utilities:

 * WBX transceiver board
 * SBX transceiver board
 * more to come...

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Calibration utilities
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UHD installs the calibration utilities into <install-path>/bin.
**Disconnect** any external hardware from the RF antenna ports,
and run the following from the command line.
Each utility will take several minutes to complete.
::

    uhd_cal_rx_iq_balance --verbose --args=<optional device args>
    uhd_cal_tx_iq_balance --verbose --args=<optional device args>
    uhd_cal_tx_dc_offset --verbose --args=<optional device args>

See the output given by --help for more advanced options, such as:
manually choosing the frequency range and step size for the sweeps.

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Calibration data
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Calibration files are stored in the user's home/application directory.
They can easily be moved from machine to another by copying the "cal" directory.
Re-running a calibration utility will replace the existing calibration file.
The old calibration file will be renamed so it may be recovered by the user.

 * **Unix:** ${HOME}/.uhd/cal/
 * **Windows:** %APPDATA%\\.uhd\\cal\\