Re: [Discuss-gnuradio] Tx path questions

[Ronaldo Nunez]

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 <address@hidden>

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

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

Santa Maria - RS - Brasil