LimeSDR-Mini GR-3.8 Block Transmit Distortion

Just received my LimeSDR-Mini 1 week ago:

  • GNU Radio 3.8
  • Ubuntu 20.04
  • With GNU Radio Flowgraph BPSK transmit, received spectrum seems distorted and bits not recovered - Spectrum as follows on transmit and receive to compare (Frequency sink before Lime Tx block is bottom spectrum in Figure). Flowgraph as follows below also:
  • FM transmit and receive worked on another flowgraph well enough to hear wav file, BPSK flowgraph booted with lime with no issues noted, and LimeQuickTest passed. Transmit spectrum on Pluto Receive looked distorted/same too when lime transmitted to it.
  • 20 dB attenuator used in loop, many gain levels, saturation checked, RF loop cable disconnected and reconnected to verify receive signal above noise floor, 10 minute increments of testing only to keep lime board temperature low, tried many frequencies - sometimes transmit frequency same as receive frequency and sometimes not (offset with NCO parameter).

Assuming no mistake in setup, is there a gr-limesdr block 3.8 branch issue maybe where the “Cal” on limesdr-mini board is not occurring well when directed by gnu radio flowgraph?
Seems like limeboard is OK, but maybe it is not calibrating well when controlled via a gr-limesdr block in gnu radio 3.8?

Any thoughts?
Thank You

Your spectrum shows periodic spikes - one of my computers generates spikes like those - so I cannot use it when the interference is important.

RightHalfPlane,

The spikes exist because I used a relatively short repeating data pattern on that run. I also did runs with a long repeating data pattern but no difference on this issue. Spectrum shown below on that run with long repeating patterns.

You are correct though implying short repeating patterns with those spikes should not be used operationally and that was a good point and needed to be eliminated as a possible cause for this issue.

Regards,
Dave M

Update:

  • Transmitted via Windows SDRangel with DATV channel and LimeSDR-mini at 2.0 Msymbols/s and received on another laptop with Pluto. At Pluto source output, received spectrum with Lime/SDRangel transmitting looks fine with good received I/Q Constellation. See attached figure below.
  • Therefore, seems like my LimeSDR-mini board is working and can be configured with good quality BPSK transmit output signal with SDRangel-Windows, but not with GNU Radio 3.8 blocks and Ubuntu 20.04 for BPSK and QPSK transmissions. My board just came off the assembly line in May.
  • Does Myriad/LimeMicro concur and if yes is there a plan to upgrade the GR-LimeSDR 3.8 blocks or add an issue tracker on github for planned software upgrades later to GR-Limesdr blocks for 3.8?

Thank You,
DaveM