UHD Calibration continued

I have been looking more at the performance of the udh_cal_* routines to
try
and understand the operation of my N210 and the SBX card. I found the
cal
files that I had previously generated and moved them into a separate
directory to prevent the UHD driver from finding them. From the
documentation, I think this should apply no corrections. Then I removed
the
antennas and terminated both inputs with 50 ohm terminators, running
uhd_fft.grc with a frequency of 2.0087MHz (which is away from other
spurious
signals and near a calibration point), a sampling rate at 5M, a 2.048k
FFT
size, and an average of 0.004 produces a graph where I can observe both
the
average leakage power of the LO and the average noise floor. This
produced
data for the LO [A - -99.21 dB, FFT: -106.14 dB] and noise [A: -117.138,
FFT: -117.1 dB].

I then ran uhd_rx_iq_balance which produced the file
/home/gnube/.uhd/cal/rx_iq_cal_v0.1_E2R12X1XS.csv.

With correction line of 2.0087e+09, 0.961492, -0.307198, 76.7275,
38.7414

Running uhd_fft.grc again produced no change to the measurements.

I then ran uhd_tx_iq_balance which produced the file
/home/gnube/.uhd/cal/tx_iq_cal_v0.1_E2R12X1XS.csv.

With correction line of 2.0087e+09, 0.962229, 0.0709783, 77.7254,
39.0847

Running uhd_fft.grc again produced no change to the measurements.

I then ran uhd_tx_dc_offset which produced the file
/home/gnube/.uhd/cal/tx_dc_cal_v0.1_E2R12X1XS.csv.

With correction line of 2.0087e+09, -0.0108594, -0.00078125, -95.2992,
51.6633

Running uhd_fft.grc again produced no change to the measurements.

Can anyone tell me what mistake I am making?

Evan M.

On 12/14/2011 01:55 PM, Evan M. wrote:

I have been looking more at the performance of the udh_cal_* routines to try
and understand the operation of my N210 and the SBX card. I found the cal
files that I had previously generated and moved them into a separate
directory to prevent the UHD driver from finding them. From the
documentation, I think this should apply no corrections. Then I removed the

correct

antennas and terminated both inputs with 50 ohm terminators, running
uhd_fft.grc with a frequency of 2.0087MHz (which is away from other spurious
signals and near a calibration point), a sampling rate at 5M, a 2.048k FFT
size, and an average of 0.004 produces a graph where I can observe both the
average leakage power of the LO and the average noise floor. This produced
data for the LO [A - -99.21 dB, FFT: -106.14 dB] and noise [A: -117.138,
FFT: -117.1 dB].

So you are measuring the transmit LO leaking into receive? Which means
uhd_fft.grc is both transmitting and receiving?

Can anyone tell me what mistake I am making?

The cal utilities are for suppressing IQ imbalance on RX and TX and DC
level on transmit. I dont know exactly what uhd_fft.grc is, but I dont
think you are measuring IQ suppression or TX DC level.

-Josh

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