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 <e...@comsec.com> > 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
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