Re: S-band BPSK

[Daniel Estévez]

Hello Yotam,

Please keep your replies on the list.

The constellation modulator has in fact an RRC filter that cannot be 
disabled, so if you don't want that you'll need to use something else.

Modulating BPSK is rather easy (1 goes to +1, 0 goes to -1, or the other 
way around, depending on your convention), so you don't even need to use 
any of the more complicated blocks that deal with constellations. It 
might be better to do something simple that you understand well (such as 
multiply your unipolar signal by 2 and subtract 1) instead of using a 
more complicated block of which you don't understand all the details 
(yes, there are some surprising details with the constellation 
modulators and demodulators in general).

In any case, this applies to modulation (and ignores the aspect of 
pulse-shape filtering). The original topic seemed to be demodulation 
(the flowgraph you used as a starting point was a receiver).

Best,
Daniel.

On 22/06/2023 11:11, יותם זיס wrote:
> Hi Daniel,
> Thank you for answering us, we’re big fans of your work.
> in our experience the constellation modulator block doesn’t work very 
> well since it has a built-in rrc filter that didn’t quite work for us. 
> We were recommended to use the constellation encoder block instead and 
> to use your flowgraph as an example. Do you think we should go back to 
> using the constellation modulator?
> Thanks
>
> נשלח מה-iPhone שלי
>
> > ‫ב-21 ביוני 2023, בשעה 23:26, ‏‏Daniel Estévez ‏<daniel@destevez.net> 
> > כתב/ה:‬
> >
> > On 21/06/2023 17:17, יותם זיס wrote:
> > > Hi everyone,
> > > I'm trying to convert Daniel Estevez's QPSK flowgraph to BPSK and I'm 
> > > having some issues. I tried replacing the FIR filter with an RRC 
> > > filter and modifying the parameters.
> > > The transmission looks fine but it won't demodulate properly.
> > > I'm attaching the flowgraph's grc file and screenshots, the upper GUI 
> > > window is the modulation and the lower one is the demodulation.
> > > Would love some tips and corrections,
> > > Thanks and 73
> > > Original flowgraph
> > > https://github.com/daniestevez/jupyter_notebooks/blob/master/ArtemisI/oqpsk_demodulator.grc
> > >  
> > > <https://github.com/daniestevez/jupyter_notebooks/blob/master/ArtemisI/oqpsk_demodulator.grc>
> >
> > Hello,
> >
> > That flowgraph is a not-so-good (but successful) approach at OQPSK 
> > demodulation specifically made for Artemis-1 (it could fail with other 
> > OQPSK waveforms depending on the pulse-shape filtering).
> >
> > If you want to demodulate BPSK, why don't you use the BPSK demodulator 
> > from gr-satellites of follow this example?
> >
> > https://wiki.gnuradio.org/index.php/Simulation_example:_BPSK_Demodulation
> >
> > Best,
> > Daniel.

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