Re: LimeSDR | Sinewave test | Glitchy behavior

[Christophe Seguinot]

Hi all

There is something wrong in this simulation.

Attached is a flowgraph with a selectable Lime SDR Source, and a RTL-SDR dongle as receiver. I tested this with a Lime SDR Mini.

• I was suspecting a Lime SDR issue, however this is not so clear.
  
• As Anish I also tested a const source.
  
• The flowgraph is running fluently and I dont' see any error message about transmission to Lime SDR
  

Conclusion of my simulations :

• with a const source (=1) at Lime input : everything is OK, the received signal is frequency shifted (normal) and the SNR is correct if LimeSDR Gain is sufficient
• Using ratioanal resampler followed by WBFM Transmit Same reslt, everything is OK
  
• First source+ WBFM + Rational resampler (this is a sample file found on LimeSDR website
  
• the spectrum is not correct (look like  a modulated signal
• the received signal magnitude is not constant
• BUT the send signal on the Time Sink look like correct. ( I.E =1+j0 as for others sources, whitout any glicht)
  

How can we further investigate this?

On 18/03/2021 13:13, Anish Mangal wrote:

And, if I try the attach gnuradio file, which is just a constant source of value '1' going to the limesdr sink block, I actually see a sine-ish wave without the glitchy behavior.

On Thu, Mar 18, 2021 at 5:31 PM Anish Mangal <anishmg@umich.edu> wrote:

I tried your grc and got the same result.

See the waveform's envelope in this oscilloscope capture. Note the timebase.

https://drive.google.com/file/d/1b7PnpmvFfdQTDIwALuOzb22AzeffzR2w/view?usp=sharing

This isn't happening in SDRAngel.

On Thu, Mar 18, 2021 at 3:49 AM Cinaed Simson <cinaed.simson@gmail.com> wrote:

I moved the rational resampler block from the output side to the input side of the WBFM.

The output of WBFM block needs to match the input of your LimeSDR.

I don't have the LimeSDR software installed so I couldn't look inside the sink block.

-- Cinaed

P.S - yes, you can post GRC's on the mailing list  - they're text based.

On 3/17/21 4:14 AM, Anish Mangal wrote:

I linked the grc file in the original email. Attaching it here as well. (Don't know if the mailing list allows attachments)

On Wed, Mar 17, 2021 at 1:40 PM Cinaed Simson <cinaed.simson@gmail.com> wrote:

Hi Anish - since this is a gnuradio mailing list, the starting point would be to post your GRC - which is an yaml or text file.

-- Cinaed
 

On 3/16/21 11:19 PM, Anish Mangal wrote:

Hi! Any pointers to where I can start debugging this?

Maybe run gnuradio-companion in debug mode?

Do more simpler tests?

Any other suggestions?

I have a HackRF One and will try the exact same comparison there too ... SDRAngel & grc

On Mon, Mar 15, 2021 at 7:32 PM Anish Mangal <anishmg@umich.edu> wrote:

Hi,

To properly explain the issue I'm facing, I recorded a video showing Oscilloscope waveforms. 

https://drive.google.com/file/d/11anGShu-I3NhL9Jet6YAiyBprvwP4kDc/view?usp=sharing

The gnuradio flowgraph is here:

https://drive.google.com/file/d/1xQz1Kp_feAO1YrZRXXnMF25XEGgqVPSw/view?usp=sharing

The various versions of the software/hardware involved are the following.

gnuradio-companion: 3.8.2.0 (Python 3.6.9)

gr-limesdr: branch gr-3.8 (last commit 47511dd58de1695b70e1028366411bada85eb60f)

sdrangel: 4.12.1

OS: Linux Mint 19.1

CPU: Intel© Core™ i7-4900MQ CPU @ 2.80GHz × 4

RAM: 16GB

H/w: Thinkpad T440p

tl;dr

I'm trying a simple test to create a sinewave output from a WFM modulator block. If there is no audio input, its WFM modulated signal should be a simple sinewave. If I test this with SDRAngel, I see a clean-ish actual sinewave in time domain on the oscilloscope. But if I try to do the same with gnuradio, it seems to produce a glitchy signal.

Could I have any advice on what I might be doing wrong?

Thanks,

Anish // VU2TVE

limesdr-fm-tx-test_2.grc
Description: application/gnuradio-grc