Re: LimeSDR | Sinewave test | Glitchy behavior

[Anish Mangal]

Okay. That seems to be one of the issues. Once I move the rational resampler block to after the WBFM block, it seems to go away.

However, there is still a very perceptible difference in the quality of the signal (gnuradio v/s sdrangel), and there seems to be a lot of noise in the gnuradio-produced one.

This looks like it may be a function of the settings being set on LimeSDR.

I can share the settings files that I see after gnuradio and sdrangel have run, and perhaps the differences between the two could be compared. I wonder if this is the right mailing list for it.

On Thu, Mar 18, 2021 at 6:00 PM Ron Economos <w6rz@comcast.net> wrote:

You're probably underflowing then (your CPU is not able to deliver enough samples to the LimeSDR sink block). With the FM flow graph, reduce the sweep time on your o-scope to see if you're actually transmitting 100% of the time.

Ron

On 3/18/21 05:13, 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

gnuradio-lime-settings.ini
Description: application/wine-extension-ini

sdrangel-lime-settings.ini
Description: application/wine-extension-ini