UHD - Calibration Application Notes

Table of Contents


UHD software 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 software 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 software 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:

  • RFX Series transceiver boards
  • WBX Series transceiver boards
  • SBX Series transceiver boards
  • CBX Series transceiver boards

Calibration Utilities

UHD software 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.

Note: Your daughterboard needs a serial number to run a calibration utility. Some older daughterboards may not have a serial number. If this is the case, run the following command to burn a serial number into the daughterboard's EEPROM:

<install dir>/lib/uhd/utils/usrp_burn_db_eeprom --ser=<desired serial> --args=<optional device args>

Calibration Data

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.

  • Linux: ${HOME}/.uhd/cal/
  • Windows: %APPDATA%\.uhd\cal\