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Discuss RTL-SDR and cheap software defined radio
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PostPosted: Mon Jul 31, 2017 6:45 pm 
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Joined: Mon Jul 31, 2017 6:12 pm
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I am new to SDR. Should it be possible for me to capture AM digital signals demodulated from 902-928 MHz with the RTL-SDR?

I'm currently using CubicSDR. I tried a couple of others, but Cubic is the application that worked for me first. I want to capture the waveforms shown in the 'scope window, top right, to some kind of file where I can decode the edge timings and reconstruct the data. The signal shown is UHF RFID, specifically ISO18000-6C aka UHF Gen2. The Scope window looks like what I actually see on o'scopes with an envelope detector. I think if I could capture what's shown in that window, I could decode the bitstream in software, and end up with a sniffer toolchain for the RFID air interface using RTL-SDR.

I've been nibbling at the problem all day. Windows standard audio capture seems to apply audio filters to the signal, which is bad. Cubic says it works with Jack, but I installed that and Cubic doesn't see it as an output device. Building my own Cubic to hack it up requires building wxwidgets in VS2015, which seems fraught. Writing my own Cubic alternative, either over the drivers or librtlsdr, seems pretty hard.

It seems there should be a relatively painless way to capture the unfiltered demodulated AM take from Cubic or a similar application, so I could just write some software to decode the KHz edges. My main development system is Win10 but I have Win7 and Fedora systems around too.

To the people posting here, who already know the technology, where should I be looking? SoapyRemote?

Thanks,
Larry


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PostPosted: Wed Aug 02, 2017 1:51 pm 
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Joined: Sun Oct 09, 2016 7:27 am
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GNU Radio?
Do you adjust the Rate of your Soundcard? Go to the Soundcard Settings in Windows and change it.


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PostPosted: Thu Aug 03, 2017 9:15 pm 
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Joined: Mon Jul 31, 2017 6:12 pm
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Thank you. I raised my sound card from 48kHz to 192kHz. Gnu Radio looks like it will do the job. I did read that it had poor SDR support a few years ago. I guess I'll find out how it is now.


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PostPosted: Thu Aug 10, 2017 1:34 pm 
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Joined: Mon Nov 19, 2012 11:54 pm
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Yes use GNU Radio, it has excellent SDR support these days. Most experimental SDR decoders are written in GNU Radio.


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