Forum: GNU Radio Tx path questions

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4960c18fe86cafa1f819b4db3e2d758a?d=identicon&s=25 Ronaldo Nunez (Guest)
on 2009-01-05 13:50
(Received via mailing list)
Hello,

I have a doubt about coarse modulation in AD9862 (tx path).
I saw in the faq (http://gnuradio.org/trac/wiki/UsrpFAQ/ADC)  "...Block
B
only moves the signal +/- fs/4 or fs/8"...
OK, but when it moves fs/4 and when it moves fs/8? Is that controllable
by
software?


Another question:
Is the DAC frequency (fdac in the AD9862 datasheet) the same as
target_freq parameter in the tune function?

Thank you

Regards

--
__________________________________
Ronaldo A. Viera Nunez
Acadêmico/Engenharia Elétrica
Universidade Federal de Santa Maria

Santa Maria - RS - Brasil
745d8202ef5a58c1058d0e5395a78f9c?d=identicon&s=25 Eric Blossom (Guest)
on 2009-01-05 18:11
(Received via mailing list)
On Mon, Jan 05, 2009 at 09:48:47AM -0300, Ronaldo Nunez wrote:
> Hello,
>
> I have a doubt about coarse modulation in AD9862 (tx path).
> I saw in the faq (http://gnuradio.org/trac/wiki/UsrpFAQ/ADC)  "...Block B
> only moves the signal +/- fs/4 or fs/8"...
> OK, but when it moves fs/4 and when it moves fs/8? Is that controllable by
> software?

It's transparently controlled by software.  Look at usrp_standard.{h,cc}

> Another question:
> Is the DAC frequency (fdac in the AD9862 datasheet) the same as
> target_freq parameter in the tune function?

fdac is a constant, 128MHz.  target_freq is the RF frequency that you
desire to have appear at 0 Hz in the complex baseband.

Eric
4960c18fe86cafa1f819b4db3e2d758a?d=identicon&s=25 Ronaldo Nunez (Guest)
on 2009-01-06 14:42
(Received via mailing list)
Thank you for your answer Mr. Blossom,
So, the tx path is something like this:

PC --> USB --> CIC(FPGA) --> AD9862 --> Daughter Board --> Antenna

There is two frequencies involved in all transmissions:
* A signal frequency (f_signal), generated by sig_source_c().
* A RF frequency (f_tx), set with target_freq in tune().

The signal (which frequency is f_signal) is interpolated by a factor
between
4 and 512 on CIC interpolator,
after it is up converted to the RF frequency (by the NCO on fine
modulator),
so it is moved +- fdac/4 or fdac/8 on coarse modulator.
The signal will be converted to analog (DAC) and amplified and
transmitted.


Be free to correct me, I need to know exactly how USRP and GNUradio
works.

Thanks for all!

Best regards,

Ronaldo Nunez




2009/1/5 Eric Blossom <eb@comsec.com>

>
>
--
__________________________________
Ronaldo A. Viera Nunez
Acadêmico/Engenharia Elétrica
Universidade Federal de Santa Maria

Santa Maria - RS - Brasil
745d8202ef5a58c1058d0e5395a78f9c?d=identicon&s=25 Eric Blossom (Guest)
on 2009-01-06 18:48
(Received via mailing list)
On Tue, Jan 06, 2009 at 10:41:22AM -0300, Ronaldo Nunez wrote:
> 4 and 512 on CIC interpolator,
> after it is up converted to the RF frequency (by the NCO on fine modulator),
> so it is moved +- fdac/4 or fdac/8 on coarse modulator.
> The signal will be converted to analog (DAC) and amplified and transmitted.
>
>
> Be free to correct me, I need to know exactly how USRP and GNUradio works.

Yes, you've got the basic path right.


Please see also the USRP FAQ, available here

  http://gnuradio.org/trac/wiki/UsrpFAQ

or as a pdf

  http://gnuradio.org/trac/attachment/wiki/UsrpFAQ/U...

Eric
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