[USRP-users] Transmit DC Offset Calibration

Steve Peters stevenpeters at gmail.com
Wed Jun 20 00:34:38 EDT 2012


Hello,

I'm hoping there is a crucial step to the DC calibration that I'm
overlooking.  The DC offset calibration is only making my DC offset worse.

For my setup, I'm using tx_waveforms --freq=301e6 --rate=1e6
--wave-type=CONST --ampl=0.0. Without the calibration, the received sine
wave has an amplitude of about 0.004, and with the calibration the
amplitude is about 0.01 (transmission over a wire with 30dB attenuation to
attempt fairness between tests).  This is well above the noise floor.

I've tried setting --nsamps=1000000 and focusing on the narrow band that
I'm operating in, but it never seems to actually reduce the DC offset.

When running the calibration, I disconnect the internal SMB cable from the
GDB.  Am I missing some other crucial step to the calibration?

I'm running UHD 3.4.1 on USRP N210s, rev4.

When the TX and RX are connected to a common 10 MHz source, the sine wave
goes away (as expected).  Unfortunately this isn't a long term solution to
the problem for me.

Best regards,
Steve
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