How do I "see" the digital data being transmitted?

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m4l490n
Posts: 6
Joined: Mon Jan 09, 2017 10:37 pm

How do I "see" the digital data being transmitted?

Post by m4l490n » Mon Jan 09, 2017 11:15 pm

Hello everybody

I have a NooElec dongle and I have downloaded the http://www.rtl-sdr.com/new-rtl-sdr-pano ... -analyzer/ and the http://airspy.com/download/ software to use with the dongle. I need to analyze some signals on the 910MHz to 920MHz spectrum and I have a silicon labs development tool working and transmitting a custom packet at 910MHz.

So far, in both programs, I can see how the signal is registered on the waterfall diagram when I press the button on the dev tool and it transmits the packet.

The first image is from Panoramic Spectrum analyzer.
Packet Transmitted 910MHz.png
Packet Transmitted 910MHz.png (219.38 KiB) Viewed 5860 times
And the second from AirSpy.
AirSpy Packet Transmitted 910MHz.png
AirSpy Packet Transmitted 910MHz.png (177.4 KiB) Viewed 5860 times
It can be seen perfectly how the transmission is being visualized in both programs in the graph as well as the waterfall. So I can "see" the signals being sent from the transmitter.

So the question here is, What software can I use to "see" the digital data being sent and not just the signal?

Because I need to configure my receiver to receive packets from some devices but I haven't been able to do so. The thing is that I'm not completely sure that these devices are sending the packets correctly. So I need to see not just that there is a transmission but the data being transmitted as well. This would help me greatly.

Thanks for helping!! :)

AD5NL
Posts: 34
Joined: Fri Sep 16, 2016 7:00 pm

Re: How do I "see" the digital data being transmitted?

Post by AD5NL » Mon Jan 09, 2017 11:28 pm

What mode is being transmitted?

rtlsdrblog
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Re: How do I "see" the digital data being transmitted?

Post by rtlsdrblog » Tue Jan 10, 2017 12:47 am

If its a OOK or similar signal you could just record the audio in AM mode and open it up in an audio processing program like Audacity. Then you can see the 1's and 0's in the waveform.

m4l490n
Posts: 6
Joined: Mon Jan 09, 2017 10:37 pm

Re: How do I "see" the digital data being transmitted?

Post by m4l490n » Tue Jan 10, 2017 1:09 am

rtlsdrblog wrote:If its a OOK or similar signal you could just record the audio in AM mode and open it up in an audio processing program like Audacity. Then you can see the 1's and 0's in the waveform.
Yes, it's actually modulated in OOK and Manchester encoded. But, can I record the audio in AM even at 910MHz?

rtlsdrblog
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Re: How do I "see" the digital data being transmitted?

Post by rtlsdrblog » Tue Jan 10, 2017 6:20 am

Yes the audio is demodulated and baseband, its not at 910 MHz. Just open up audacity and hit record while your playing the data through AM in SDR#.

m4l490n
Posts: 6
Joined: Mon Jan 09, 2017 10:37 pm

Re: How do I "see" the digital data being transmitted?

Post by m4l490n » Tue Jan 10, 2017 4:26 pm

rtlsdrblog wrote:Just open up audacity and hit record while your playing the data through AM in SDR#.
And how do I connect one another? because audacity is recording from the MIC and I can't find the option to somehow connect it to SDR#

nullwolf
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Joined: Wed Jan 11, 2017 3:10 am

Re: How do I "see" the digital data being transmitted?

Post by nullwolf » Wed Jan 11, 2017 3:13 am

IMO you'd be better off recording the transmission using Osmocom FFT, then loading the saved file into Inspectrum.

If you're looking for something that's slightly more automated (i.e. you don't want to manually determine which symbols are 1s and 0s in a visualisation tool), run Inspectrum through Dspectrum (a little wrapper I whipped up some time ago) and you'll get the bin/hex output instead of having to do it manually. Note that for DSpectrum, not all modulation types are supported, but as it is OOK you'll be ok. I don't recall building in manchester decoding into the version that I published on GitHub, but you'll get the 'raw' output at least if that's the case.

rtlsdrblog
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Re: How do I "see" the digital data being transmitted?

Post by rtlsdrblog » Wed Jan 11, 2017 11:09 pm

m4l490n wrote:
rtlsdrblog wrote:Just open up audacity and hit record while your playing the data through AM in SDR#.
And how do I connect one another? because audacity is recording from the MIC and I can't find the option to somehow connect it to SDR#
You might need to enable stereo mix http://www.rtl-sdr.com/tutorial-how-to- ... windows-7/. Once you've got Audacity going and you understand what you're seeing, then you can try what nullwolf suggested, using Inspectrum and Dspectrum.

m4l490n
Posts: 6
Joined: Mon Jan 09, 2017 10:37 pm

Re: How do I "see" the digital data being transmitted?

Post by m4l490n » Sat Jan 14, 2017 9:01 pm

nullwolf wrote:IMO you'd be better off recording the transmission using Osmocom FFT, then loading the saved file into Inspectrum.

If you're looking for something that's slightly more automated (i.e. you don't want to manually determine which symbols are 1s and 0s in a visualisation tool), run Inspectrum through Dspectrum (a little wrapper I whipped up some time ago) and you'll get the bin/hex output instead of having to do it manually. Note that for DSpectrum, not all modulation types are supported, but as it is OOK you'll be ok. I don't recall building in manchester decoding into the version that I published on GitHub, but you'll get the 'raw' output at least if that's the case.
Thanks!

I'm ok getting the raw output, nevertheless, I tried it and it's not working for me. I include a couple of images for you to see. I'm following the steps on the video but the amplitude plot is not working properly.
dspectrum-issue-1.png
dspectrum-issue-1.png (275.16 KiB) Viewed 5671 times

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