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I want to transmit QPSK modulated signal and simply receive it simultaneously to a file using SDR platform (Bladrfx40), but no output shows on received side.

Here is the flow graph I implemented: Flow Graph

Here is what I want to receive and what is being transmitted: fft transmit

Here is what I actually receive: fft receive

Constellation plot on transmitter side: image

Constellation plot on receiver side: image Zoomed Constellation on receiver side image Can i know where i am lacking in my procedure?

Khan
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  • soooo first of all, I still have to say that more than 5 years after we announced it (it's getting tiresome): GNU Radio will remove the WX components from the upcoming release. Do not build new flowgraphs with WX GUI – use Qt GUI instead, it's faster and unlike WX we can still maintain it. Also, Packet encoder and Packet decoder are both in the **deprecated** category for a reason – they have bugs that can't be fixed. Please don't use them. – Marcus Müller May 26 '19 at 12:08
  • So, it's not quite clear what your problem with the reception is. This looks fine to me. Can you explain how this differs from what you were expecting? – Marcus Müller May 26 '19 at 12:09
  • The receiver side output is not exactly i am transmitting, since the constellation plot has a lot of difference ( shown in the post) – Khan May 26 '19 at 16:56
  • Also, i have changed WX to QT and removed packet encoder. The constellation plot shown in the post is after making these changes. – Khan May 26 '19 at 17:02
  • I'm sorry, I don't see how it has "a lot of difference": Can you put how you think the spectra differ into words? I'm not doing this to annoy you, I just don't understand what you're expecting! – Marcus Müller May 26 '19 at 20:07
  • Constellation plot i am talking about. It should be dotted spheres at four different ends. – Khan May 26 '19 at 21:21
  • well, you've forgotten to zoom in on that, so I can't really make a statement there! – Marcus Müller May 26 '19 at 21:53
  • I had zoomed it, it was nothing like that. Post edited with the zoomed version. – Khan May 27 '19 at 16:38
  • ah, this looks like you've got insufficient receive gain, so that your values are quantized. Also, doesn't look like you have any phase synchronization? – Marcus Müller May 27 '19 at 20:46
  • How to achieve that? Is the problem of gain only or what? – Khan May 27 '19 at 21:16
  • um, as I said, at least gain, and lack of phase sync. – Marcus Müller May 27 '19 at 21:51

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