DQPSK demodulation.

Kim Mortensen kimfmx at gmail.com
Mon Feb 17 20:46:56 UTC 2020


Hi,

Would someone happened to have a sample file containing I/Q data from a
DQPSK signal. The content is not important, as long as its DQPSK -
Preferably in wav format.

Best Regards
Kim Mortensen

Den lør. 15. feb. 2020 kl. 09.33 skrev Kim Mortensen <kimfmx at gmail.com>:

> Hi,
>
> Thanks for the add, I have been hinted this place, and im looking forward
> to digging deeper into the realm of TETRA / DQPSK.
>
> What im trying to do is write a C# program for demodulation of TETRA. and
> have come so far as to be able to view the IQ vector run around on the
> unity circle, but it appears a bit distorted. I think its due to a crude
> low pass filter i used on the I/Q signal causing this. From reading books
> and sites i find that I should probably used a raised cosine filter to keep
> the signal form beeing distorted (ISI). am i correct in my assumption? and
> do you have the open source code i can inspect, regardless if programming
> language.
>
> I know there is tons of programs out there that can decode and even
> produce audio from TETRA DQPSK signals, and I have one installed, but i
> want to have an edge to this, i need to understand and learn first hand. It
> may take time, but thats how it is.
>
> I have what is required regarding programming skills and radio knowledge -
> I am radio Amateur, and 20 years ago i did have Digital communication
> classes at Engineering college - But thats 20 years ago, and the equations
> in the books are kind of far away in my head.. but the theory sticks.
>
> Please help me get up to speed in decoding DQPSK, im not expecting to do
> this quickly, but will be in steps when i have time, and will lead to
> questions. But at some point i could be on your frontier digging into TETRA
> as a whole.
>
> Best Regards
> Kim Mortensen
>
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