DC Offset Calibration Returns Different Values Each Run

[Stephen Ochs]

I have a bladeRF micro 2.0 A4. I am seeing what appears to be a roughly 10 dB spike at the tuning frequency due to DC offset in my received data. However, when I run the RX DC calibration in bladeRF-cli (

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calibrate dc rx

), I see varying results, and if I set these values (

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calibrate dc rx <I> <Q>

), it doesn't seem to help. Is it normal for these values to vary so much?

This is the result of running it a few times in a row:

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bladeRF> calibrate dc rx

RX DC I: Value = -1728, Error =  0.059
RX DC Q: Value = -1824, Error =  1.372

bladeRF> calibrate dc rx

RX DC I: Value = -1952, Error =  0.003
RX DC Q: Value = -1824, Error =  1.314

bladeRF> calibrate dc rx

RX DC I: Value = -1888, Error =  0.019
RX DC Q: Value = -1728, Error =  1.419

bladeRF> calibrate dc rx

RX DC I: Value = -1984, Error =  0.132
RX DC Q: Value = -1824, Error =  1.349

These were the settings prior to running the calibration:

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bladeRF> print

  RX1 Bandwidth:  24000000 Hz (Range: [200000, 56000000])
  RX2 Bandwidth:  24000000 Hz (Range: [200000, 56000000])
  TX1 Bandwidth:  24000000 Hz (Range: [200000, 56000000])
  TX2 Bandwidth:  24000000 Hz (Range: [200000, 56000000])

  RX1 Frequency:  100000000 Hz (Range: [70000000, 6000000000])
  RX2 Frequency:  100000000 Hz (Range: [70000000, 6000000000])
  TX1 Frequency:  100000000 Hz (Range: [47000000, 6000000000])
  TX2 Frequency:  100000000 Hz (Range: [47000000, 6000000000])

  Tuning Mode: Host

  Bit Mode: 16 bit samples

  Feature:  Default enabled

  RX1 AGC: Disabled
  RX2 AGC: Disabled

  Clock reference: none
  Clock input:     Onboard VCTCXO
  Clock output:    Disabled

  RX1 RSSI: preamble = -64 dB, symbol = -49 dB
  RX2 RSSI: preamble = -65 dB, symbol = -50 dB

  Loopback mode: none

  RX mux: BASEBAND - Baseband samples

  RX FIR Filter: normal (default)
  TX FIR Filter: bypass (default)

  Gain RX1 overall:   60 dB (Range: [-16, 60])
              full:   77 dB (Range: [1, 77])
  Gain RX2 overall:   60 dB (Range: [-16, 60])
              full:   77 dB (Range: [1, 77])
  Gain TX1 overall:   56 dB (Range: [-23.75, 66])
               dsa:  -90 dB (Range: [-89.75, 0])
  Gain TX2 overall:   56 dB (Range: [-23.75, 66])
               dsa:  -90 dB (Range: [-89.75, 0])

  RX1 sample rate: 32000000 0/1 (Range: [520834, 61440000])
  RX2 sample rate: 32000000 0/1 (Range: [520834, 61440000])
  TX1 sample rate: 32000000 0/1 (Range: [520834, 61440000])
  TX2 sample rate: 32000000 0/1 (Range: [520834, 61440000])

  Bias Tee (RX1): off
  Bias Tee (RX2): off
  Bias Tee (TX1): off
  Bias Tee (TX2): off

  Current VCTCXO trim: 0x1e21
  Stored VCTCXO trim:  0x1e21

  Hardware status:
    RFIC status:
      Tuning Mode:  Host
      Temperature:  27.2 degrees C
      CTRL_OUT:     0xf8 (0x035=0x00, 0x036=0xff)
    Power source:   USB Bus
    Power monitor:  4.92 V, 0.56 A, 2.76 W
    RF routing:
      RX1: RFIC 0x0 (A_BAL  ) <= SW 0x0 (OPEN   )
      RX2: RFIC 0x0 (A_BAL  ) <= SW 0x0 (OPEN   )
      TX1: RFIC 0x0 (TXA    ) => SW 0x0 (OPEN   )
      TX2: RFIC 0x0 (TXA    ) => SW 0x0 (OPEN   )

These are the versions:

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bladeRF> version

  bladeRF-cli version:        1.9.0-git-e50f28fb
  libbladeRF version:         2.5.0-git-e50f28fb

  Firmware version:           2.4.0-git-a3d5c55f
  FPGA version:               0.15.3 (configured from SPI flash)

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