Unusual LimeSDR Mini RX spurs/artifacts

Projects LimeSDR
1

My LimeSDR Mini has been running fine for a while, hooked up to two LNAs and a filter running a 20 MSPS. When the LNAs are powered on, I typically get a noise floor of approximately 11 dB. Today, however, I noticed the level is around 0 dB:

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This was the first sign that something wasn’t right. As you can see, there are tons of spikes in the power vs time plot.

This is what a good observation would look like 2 days ago:

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(The Sun drifting through the antenna, with a tiny bit of external RFI which is fine)

I then decided to completely unplug the cables from the Lime, and try acquiring some data, in order to see if the spikes that popped up out of the blue were related to the antenna/LNAs, or the SDR itself.

Indeed, this is a 30-sec acquisition with the Lime alone (with nothing connected to the port), and I get some short wideband spurs/artifacts:

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Has anyone noticed anything like this before? What could be the cause? It’s very odd to see this pop up out of the blue after many successful days of observations.

(My block diagram is ANT → LNA → Filter → LNA → Coax → Lime)

2

Could you:

  • Disconnect any cabling from the RF ports
  • Ensure the board is cool and not warm from operation
  • Run LimeQuickTest while the board is cold

Then post the results here.

1 Like
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@andrewback - Thanks for your response.

I did notice Wi-Fi adapter I had placed very close to the lime created some of these spurs (being picked up by the RF traces etc., despite no antenna). After plugging that out however, I’m still not quite sure if these artifacts are supposed to appear under nominal conditions:

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Lots of variability both in the spectrum and time domain (see waterfall).

  • Disconnect any cabling from the RF ports

Nothing is connected to the RF ports.

  • Ensure the board is cool and not warm from operation

It is being cooled with a fan, it’s not getting hot at all.

  • Run LimeQuickTest while the board is cold

Output (ignore the wrong date):

[ TESTING STARTED ]
->Start time: Sun Oct 18 22:02:52 2020

->Device: LimeSDR Mini, media=USB 3.0, module=FT601, addr=24607:1027, serial=1D424AFA04BBCD
  Serial Number: 1D424AFA04BBCD

[ Clock Network Test ]
->REF clock test
  Test results: 6863; 20060; 33257 - PASSED
->VCTCXO test
  Results : 6711032 (min); 6711187 (max) - PASSED
->Clock Network Test PASSED

[ FPGA EEPROM Test ]
->Read EEPROM
->Read data: 12 07 1A 12 07 1A 02
->FPGA EEPROM Test PASSED

[ LMS7002M Test ]
->Perform Registers Test
->External Reset line test
  Reg 0x20: Write value 0xFFFD, Read value 0xFFFD
  Reg 0x20: value after reset 0x0FFFF
->LMS7002M Test PASSED

[ RF Loopback Test ]
->Configure LMS
->Run Tests (TX_2 -> LNA_W):
  CH0 (SXR=1000.0MHz, SXT=1005.0MHz): Result:(-13.5 dBFS, 5.00 MHz) - PASSED
->Run Tests (TX_1 -> LNA_H):
  CH0 (SXR=2100.0MHz, SXT=2105.0MHz): Result:(-14.7 dBFS, 5.00 MHz) - PASSED
->RF Loopback Test PASSED

=> Board tests PASSED <=

Elapsed time: 2.45 seconds