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## Re: Baseband signals frequency,amplitude,data rate determination.

 From: CEL Subject: Re: Baseband signals frequency,amplitude,data rate determination. Date: Fri, 14 Feb 2020 20:42:19 +0000

```Hello,

> I need the basic baseband signal (low frequency) but it would be a
0Hz frequency?

Yes, as said, it would be a band-limited signal around 0 Hz. That's the
definition of baseband signal.

I'm not sure what you mean with

> timing diagram is showing the signal has some certain frequency

A timing diagram (not _quite_ sure what that is) shows no frequency.

Are you perhaps mixing up bandwidth and frequency? Or maybe symbol
rate? (But you already have some calculations of symbol rate, so I'm
really not sure what you mean.)

Regarding bandwidth: Bandwidth of a linear modulation (without Bias) is
always fully defined by the pulse shaping filter. You have one of these

Best regards,
Marcus

PS:
might be a good place to start; you have gaps in understanding of
chapters 2.1–2.3, 2.7, and 4.1–4.2, it seems. It'll be very hard for
you to understand what your equalizer and synchronizers do.

On Fri, 2020-02-14 at 21:24 +0100, Md. Atiqur Rahman wrote:
> Thank you for the clarification.  I will update it to 3.8 soon.
> However, baseband is the main signal which will be converted to RF signal by
> means of upconverter. I have a SDR device(red-pitaya), in which two digitally
> modulated baseband signals(I-Q) will come out separately and later on with RF
> front end it will be mixed with high frequency. That is the main idea. Hence,
> first, I need the basic baseband signal (low frequency) but it would be a 0Hz
> frequency? That I have no idea of. The timing diagram is showing the signal
> has some certain frequency, then it would be 0?
> Would you please give me some details. Thank you so much.
>
> ps: WX block insertion was a mistake. I didn't realize it until you mentioned
> it. As I am going to write a report on my work as well, it is great to know
> that now the graph can be export. Is there any updates also for extracting
> GRC flow graph from file>screen capture  as well?
>
> On Fri, Feb 14, 2020 at 9:01 PM Müller, Marcus (CEL) <address@hidden> wrote:
> > Hi Md. Atiqur,
> >
> > On Fri, 2020-02-14 at 20:43 +0100, Md. Atiqur Rahman wrote:
> > > For a QPSK modulation technique, I choose to set constellation point 1 to
> > > -1, hence 1.4142 would be amplitude
> >
> > Ah, you're confusing the magnitude of the complex number with the
> > amplitude of the I and Q component.
> >
> > So, yes, the magnitude of (1 + 1j), (1 - 1j), (-1 + 1j) and (-1 -1j)
> > are 1.41, but the real and imaginary parts are still +-1.
> >
> > >  but in the timing diagram, it looks less than that.
> >
> > So, that's correct :)
> >
> > > Another point is, as my sampling rate is 2Mhz, and samples per symbol are
> > > 32, hence 62.5K is the symbol rate, what will be my baseband signal
> > > frequency?
> >
> > 0 Hz. That's what "baseband" means.
> >
> >
> > Best regards,
> > Marcus
> >
> > PS: As someone occasionallly advising students, I'd recommend
> > you clean up your flow graph; there's blocks in there you've commented
> > out that you can never use (WX can't coexist with QT GUI). Also, try to
> > make it as linear as possible, so to make it really easy to follow the
> > "sample flow" optically. This is the Nr. 1 debugging hint for GRC
> > beginners, and it really helps a lot when talking about a flow graph.
> >
> > Also, by the way, you're using a legacy GNU Radio. We've released GR
> > 3.8, and you're still on 3.7.; the new GNU Radio has fewer bugs, and
> > vector export for GRC figures, which is important to anyone writing a
> > thesis with GRC flow graph pictures ;)
>
>
```

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