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Demodulating Audio Question

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SCPD

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#1
I understand the P25 protocol (as my previous threads from years ago show me learning). My main problem right now is that I'm dependent on an expensive scanner to feed control channel data to my code instead of an inexpensive SDR dongle.

I'm looking to see how much work it would take to learn (or find code that will already do what I want) to demodulate raw audio into usable CC dump data for P25 (and possibly DMR later on). I know nothing of signal processing or demodulating. My code can grab audio piped from SDR Sharp but I don't know how to take that audio and convert it. I am not trying to process audio but only the CC data.

Does anybody have any experience taking raw audio and converting it to CC Dump data that would be able to point me in the right direction? I am programming in C# / .NET for reference but might be able to understand concepts on what needs to be done or read code in another language (possibly).
 

M105

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#2
I am assuming you are writing your own software as opposed to using DSD+ or Unitrunker. I don't know much about it but I am under the impression that the source code for the original DSD and probably OP25 is open source and available. Taking a look at those two projects might provide you a starting point.
 

SCPD

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#3
Yes. I'm writing my own software. I haven't looked at DSD yet but OP25 website is down, and I tried downloading it before I opened this thread. Wonder if it is down for good or just temporarily.
 

natedawg1604

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#4
Have you tried running DSD+ (wayyy better than the original DSD) yet? It's much easier to install than OP-25 and it displays the CC data for you (granted OP-25 is also a cool program, not sure about the website status).
 

SCPD

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#5
Yes. I use it almost daily. I am decoding the CC data and have plans for some cool applications myself in the future.

Sent from my SM-G935P using Tapatalk
 

SCPD

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#7
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SCPD

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#8
The original DSD code is easier to understand - mostly because it is built for a specific purpose. op25 sits on top of Gnu Radio which is a huge erector set of functionality.

Here's a reply I gave to someone with a very similar question:

https://www.reddit.com/r/RTLSDR/comments/592reh/writing_your_own_digital_decoder/
Thank you for the link. I completely didn't realize that I asked this question already and received a response. I might have been put off of the task as this still seems over my head although I'm understanding it more as I study for my HAM license. I'll see if I can either piece it together by tracking down a copy of the OP25 code or find it somewhere. Thanks for your detailed explanation Unitrunker in my other thread. For those looking for a direct link to the other thread, the reddit link that he posted above has a link to http://forums.radioreference.com/vo...are/294387-converting-raw-if-audio-bytes.html
 
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