Re: LimeSDR | Sinewave test | Glitchy behavior

On Thu, Mar 18, 2021 at 7:12 PM Christophe Seguinot <christophe.seguinot@orange.fr> wrote:

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

From:	Anish Mangal
Subject:	Re: LimeSDR \| Sinewave test \| Glitchy behavior
Date:	Thu, 18 Mar 2021 19:28:32 +0530