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I am currently working on a BPSK demodulator and decoder for a satellite communication system using GnuRadio.

The system uses a BPSK modulation at roughly 2GHz with a symbol rate of 200 ksymb/s. I recorded the signal directly from the transceiver module connected to my Ettus b200mini via a coax cable and some attenuation in-between using 2.4 MS/s and therefore 12 SPS.

I create the following graph for demodulating the signal, which works while using it between different SDRs for sending and receiving. But when I try to demodulate the signal from the transceiver module, I get a really noisy constellation figure (see screenshot).

The phase seems to jump very strongly and I have no idea how to fix this.

I already tried different ways of filtering, different levels of attenuation between the sender and receiver, and many different settings for the used blocks, so far nothing helped.

Can anyone help me here? Even some hints on what I could try would already be nice.

Kind regards

valkyrie

GnuRadio Graph

Respective Output of the GnuRadio Graph

Trevor Reid
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valkyrie
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  • huh, an equalizer in a satellite decoder? Where does the multipath come from? – Marcus Müller Oct 10 '20 at 13:06
  • There is (hopefully) none. Especially not in this case, since I'm just using a cable. I just read, that it might help in some cases and I therefore included it. – valkyrie Oct 10 '20 at 13:37
  • well, you're debugging things. The thing you do is **reduce**, not **increase** complexity. So, remove it. Figure out the first point in your signal processing chain where the signal doesn't look like it should. By the way, your question is not a programming question (you know how to program this, you don't know what's wrong with the signal), and thus off-topic at StackOverflow, as far as I can tell. You'd probably be better off at dsp.stackexchange. (I'd be interested to learn where it said it would help a low-bandwidth satellite link.) Also, check out gr-satellites. – Marcus Müller Oct 10 '20 at 14:35
  • Ok, thank you for your advice. I will go through the whole graph again and re-post the question on DSP. Regarding gr-satellites, I'm already using this and worked through most their applicable blocks and examples, so far without luck. – valkyrie Oct 12 '20 at 07:19

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