Re: [Discuss-gnuradio] Baseband vs. Carrier freq.

[John Andrews]

I suggest you to first look into the USRP documentation available on gnuradio website. In it you will learn how a USRP upcoverts and downconverts a signal. In gnuradio we always deal with baseband signals i.e. the signal reaching your computer from the usrp or the signal entering the usrp from the computer is always a baseband signal. 

To know more about the signal that is in the air you have to find yourself a good book on communication systems. If you are new to Signals, RF communications etc then Communication Systems by Simon Haykin is a very good start. To understand more about upconversion/downcoversion and other digital signal processing then get yourself "Understanding Digital Signal Processing" by Rick Lyons but first download the pdf of the USRP documentation and read the first 15 pages. In that the author Firas explains how the USRP works in a simple way. 

Before, you start playing around with GRC by making your own flowgraph start with benchmark_tx.py/benchmark_rx.py examples. These are like the "hello world" of "digital communications using gnuradio/usrp".

There is a GRC example for bpsk in the GRC examples folder. Check that out too.

--

John

On Wed, Jan 12, 2011 at 1:31 AM, Songsong Gee <address@hidden> wrote:

Thank you for your answer :)

Can you tell me more detail?

With my understanding, a rectangular pulse from the file source will be an envelope

and by up-conversion, a sinusoidal signal will be in the rectangular pulse?

I want to know more detail on the up-conversion,

Especially, a waveform on the air.

2011/1/12 Nick Foster <address@hidden>

Songsong,

The baseband signal you are transmitting will be upconverted by the
center frequency you specify in the USRP sink. In this case, the
signal's center frequency will be 450MHz. Likewise, the USRP source
center frequency you specify for the receiver will convert that
frequency to baseband for the rest of your receive flowgraph.

--n

On Wed, 2011-01-12 at 15:38 +0900, Songsong Gee wrote:
> I'm wondering whether my flow graph is working correctly.
>
>
> I think that my flow graph just send a baseband signal
>
>
> Sender
> flow graph / scope plot
>
>
> Recevier
> flow graph / scope plot
>
>
> Yes, it receives correctly. But my question is
>
>
> The sender seems to send just a baseband signal, not a signal whose
> center freq. is not 450 MHz
>
>
> I think that it need to be multiplied by sinusoidal signal...
>
> --
> Seokseong Jeon (aka Songsong Gee)
>
>

> _______________________________________________
> Discuss-gnuradio mailing list
> address@hidden
> http://lists.gnu.org/mailman/listinfo/discuss-gnuradio

--
Seokseong Jeon (aka Songsong Gee)

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