I have just start working with bladerf instead of former used hackrf hardware and I need to solve a problem. Currently I use the following bladerf hardware, libraries and firmware:

bladerf (2.0 micro xA9) libbladeRF version: 2.2.0-2018.12-rc3-2-ppabionic Firmware version: 2.3.2 FPGA version: 0.10.2 (configured by USB host)

I tried to simply upconvert an oqpsk baseband at 1100 MHz (4 Msps) with bladerf device using gnuradio (GRC 3.711) block osmocom-sink and I got a unexpected and pretty wierd baseband spectrum compared to hackrf hardware. For better understanding, I have attached some hardcopies:

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From my point of view, I made identical setups for hackrf and bladerf device on osmocom-sink block. Later on downconverting and demodulation works very well with hackrf hardware, with bladerf device it totaly fails.

Any suggestions, I need to check or I just made wrong ? May I need to calibrate the bladerf hardware first for proper baseband processing ?

Many thanks in advance.

Best regards calenberger

  • $\begingroup$ You should be able to tell which is correct, since you know the expected signal baseband. Could you add this information to your question? $\endgroup$
    – MBaz
    Mar 12 '21 at 23:29
  • $\begingroup$ Yes indead. The top spectrum (i.e. hackrf) is the correct one and should be considered as reference. $\endgroup$ Mar 13 '21 at 7:48
  • $\begingroup$ As Dan says, this is probably related to power. My first experiment would be do reduce the amplitude of the discrete-time baseband signal, and maybe confirm with the docs that you are providing samples within range. Second, I'd reduce the gain of the analog front end. Third, I'd transmit a pure carrier. $\endgroup$
    – MBaz
    Mar 13 '21 at 14:41
  • $\begingroup$ @MBaz, thanks for your kind support! I solved the problem just by reducing the input level to the bladerf device. $\endgroup$ Mar 13 '21 at 16:13

One source of this is spectral regrowth (overdriving a device into saturation such that the pulse shaping that limits the spectrum is degraded), but compared to typical spectral regrowth spectrums I have seen, this looks more like your signal was greatly attenuated and then amplified together with noise, and then that combined signal passed through a bandpass filter. Check if there is a 5 MHz filter earlier in the Tx chain to further support this theory, and then also try to reduce the power level at the input to the device.

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    $\begingroup$ Thank you very much for your prompt response, I really appreciate it. Seems I should focus on the baseband signal level to the bladerf sink first. I will check it asap. $\endgroup$ Mar 13 '21 at 7:59
  • $\begingroup$ Confirmed ! I have reduced the input level of osmocom-sink for the bladerf and regrowth of the spectrum disappeared completely. Fine, problem solved. $\endgroup$ Mar 13 '21 at 16:09
  • $\begingroup$ @calenberger great to hear, glad you got it resolved. $\endgroup$ Mar 13 '21 at 16:11

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