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[Discuss-gnuradio] simple mod-demod combinations doesn't work
From: |
MarkO |
Subject: |
[Discuss-gnuradio] simple mod-demod combinations doesn't work |
Date: |
Fri, 7 Oct 2016 18:16:12 -0700 (MST) |
Hi everyone,
I currently use GRC 3.7.9.1 and only its In-Tree-Modules.
PC: Lenovo Laptop W530
CPU: Intel i7-3610QM with 8GB RAM
OS: Ubuntu 16.04 64 bit
I tried to create some easy examples of different modems. My first goal is
to modulate ASCII- or WAV-files, add some noise, demodulate the data stream
and save or hear the expected result. Maybe I am wrong, but i expect an
lossless connection in GRC if I directly connect an modulator to its
appropriate demodulator - particularly when i use the default values.
The issue is, even without added noise it's not possible to get an lossless
connection in software.
My Flow-Graph looks like this:
Wav File Source --> Float to Char --> QAM Mod --> Throttle --> QAM Demod -->
Pack K Bits --> Char to Float --> Audio Sink
I use [Float to Char] to reduce data and get a byte-stream. Of course this
loss of data isn't reconstructable.
But the incoming signal at the [Audio Sink] sounds extreme noisy and clips
massively.
It is also a little bit random how bad it is - at one start i can hear what
song it is, at the next start it's just noise.
I think i can say that the Problem is the mod-demod part:
--> QAM Mod --> Throttle --> QAM Demod --> Pack K Bits -->
because this:
Wav File Source --> Float to Char --> Char to Float --> Audio Sink
works pretty well.
I attached the GRC file with the different modems to this thread. Of course
only one Mod-Demod string can be active at a time.
The results are commented with [Notes] in the GRC file. I also tried every
modulation with reduced data rate (usage of down- and upsampling).
I would be deeply greatful if someone may explain me my fallacy or how it
would just work - especially for the QAM modulation mentioned at the
beginning.
Regards,
Markus
different_MODEMs_audio_test.grc
<http://gnuradio.4.n7.nabble.com/file/n61674/different_MODEMs_audio_test.grc>
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- [Discuss-gnuradio] simple mod-demod combinations doesn't work,
MarkO <=
- Re: [Discuss-gnuradio] simple mod-demod combinations doesn't work, Sylvain Munaut, 2016/10/08
- Re: [Discuss-gnuradio] simple mod-demod combinations doesn't work, MarkO, 2016/10/09
- Re: [Discuss-gnuradio] simple mod-demod combinations doesn't work, Marcus Müller, 2016/10/09
- Re: [Discuss-gnuradio] simple mod-demod combinations doesn't work, MarkO, 2016/10/25
- Re: [Discuss-gnuradio] simple mod-demod combinations doesn't work, Marcus Müller, 2016/10/25
- Re: [Discuss-gnuradio] simple mod-demod combinations doesn't work, Fons Adriaensen, 2016/10/25
- Re: [Discuss-gnuradio] simple mod-demod combinations doesn't work, Marcus Müller, 2016/10/25
- Re: [Discuss-gnuradio] simple mod-demod combinations doesn't work, Fons Adriaensen, 2016/10/25
- Re: [Discuss-gnuradio] simple mod-demod combinations doesn't work, Kevin Reid, 2016/10/25
- [Discuss-gnuradio] Delay locked loop for the two-clock problem (was: simple mod-demod combinations doesn't work), Marcus Müller, 2016/10/26