Forum: GNU Radio Basic RX/TX

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0dfa1a815559738fc7e0f17b0cbf9e54?d=identicon&s=25 Thomas Schmid (Guest)
on 2006-05-27 21:19
(Received via mailing list)
Hi,

I have a question about the basic RX/TX boards. What should I see if I
hook the basic TX board to an oscilloscope if I send out a QPSK
signal? Here is what I do:
- I generate a QPSK signal in GnuRadio
- I send the signal to a complex file source and the signal looks right
- I send the signal to the complex USRP source and have a BasicTX on
it. The outputs TXA and TXB are hooked up to a oscilloscope on channel
1 and 2 respectively.

Now, what should I see on the oscilloscope? Is it the baseband signal?
How does the I and Q phases get mixed together? Does that depend on
the mux values? Unfortunately I couldn't find a good block diagram of
the TX path on the wiki, i.e., the link to [A system block diagram of
the USRP receiver and transmitter path] on the wiki page
"http://www.comsec.com/wiki?UniversalSoftwareRadioP... is dead.

Cheers,

Thomas
3596cfe1d579c65b9babd35e8787977c?d=identicon&s=25 Matt Ettus (Guest)
on 2006-05-30 08:43
(Received via mailing list)
On Sat, 2006-05-27 at 12:16 -0700, Thomas Schmid wrote:
>
> Now, what should I see on the oscilloscope? Is it the baseband signal?
> How does the I and Q phases get mixed together? Does that depend on
> the mux values? Unfortunately I couldn't find a good block diagram of
> the TX path on the wiki, i.e., the link to [A system block diagram of
> the USRP receiver and transmitter path] on the wiki page
> "http://www.comsec.com/wiki?UniversalSoftwareRadioP... is dead.

If you set the carrier frequency to 0 you will see the I signal on the I
channel out and the Q signal on the Q channel out.  This will only be
useful with the LFTX board since the BasicTX will block DC.

If you set the carrier frequency to something other than 0, then the I
and Q signals will be upconverted and sent to the outputs.  As long as
the carrier frequency is greater than your signal bandwidth, then you
only need either the I output or the Q output since they are now
double-sided real signals.  You can still use the I and Q connectors
with an image-reject mixer if you need.

Matt
533e669652a899ecd3b838295aef0837?d=identicon&s=25 Angilberto Muniz Sb (Guest)
on 2006-05-30 09:07
(Received via mailing list)
Sorry if it sounds silly, but why one is supposed to
get DC out of the DAC if Carrier Freq is set to zero?

What if one generates a 1Mhz QPSK in GNURadio ? Its
not zero hertz, its baseband...
Im puzzled...

Angilberto.

--- Matt Ettus <matt@ettus.com> wrote:

> > - I send the signal to a complex file source and
> Does that depend on
> > the mux values? Unfortunately I couldn't find a
> good block diagram of
> > the TX path on the wiki, i.e., the link to [A
> system block diagram of
> > the USRP receiver and transmitter path] on the
> wiki page
> >
>
"http://www.comsec.com/wiki?UniversalSoftwareRadioP...
> than 0, then the I
> Matt
>
>
>
> _______________________________________________
> Discuss-gnuradio mailing list
> Discuss-gnuradio@gnu.org
>
http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>


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3596cfe1d579c65b9babd35e8787977c?d=identicon&s=25 Matt Ettus (Guest)
on 2006-05-30 09:22
(Received via mailing list)
On Tue, 2006-05-30 at 00:05 -0700, Angilberto Muniz Sb wrote:
> Sorry if it sounds silly, but why one is supposed to
> get DC out of the DAC if Carrier Freq is set to zero?
>
> What if one generates a 1Mhz QPSK in GNURadio ? Its
> not zero hertz, its baseband...
> Im puzzled...

It isn't DC exactly, but it will have components below 1 MHz, which will
be attenuated by the transformers in the Basic boards.

Matt
533e669652a899ecd3b838295aef0837?d=identicon&s=25 Angilberto Muniz Sb (Guest)
on 2006-05-30 14:53
(Received via mailing list)
Got it -- Thanks Matt.

Angilberto.

--- Matt Ettus <matt@ettus.com> wrote:

> > Im puzzled...
>
> It isn't DC exactly, but it will have components
> below 1 MHz, which will
> be attenuated by the transformers in the Basic
> boards.
>
> Matt
>
>


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