On Wed, Oct 5, 2011 at 8:00 PM, Brook Lin <gnu.fans@yahoo.com> wrote: > Hi Nick, > > Thanks for your reply. My message under the Nabble account is still under > pending. So I have to reply you via email, if you don't mind. > > Now I understand that after the RF front-end on the daughterboard, the RF > signal has been downconverted to baseband. After the ADC, the analog signal > is converted to digital samples. Than the DDC on the FPGA further down > converts the baseband signal to some data which can be fed into the USB2.0 > interface. The DDC is similar as the RF front-end, but in digital domain. My > questions are (1) what the center frequency is for the sine/cosine generator > in Figure 3 in > http://www.gnu.org/software/gnuradio/doc/exploring-gnuradio.html. Is it > 64MHz? No. The DDC removes any residual frequency offset caused by the finite tuning steps of the RF front end. So if you ask for 142.000MHz, and the daughterboard can only tune to 142.020MHz, the DDC will shift out the last 20kHz so you effectively end up at 142.000. (2) what kind of daughterboards are using zero-IF receiver technology? and > which are not using, such as TVRX? TVRX and TVRX2 are low-IF. The rest of them are direct conversion. --n > Thanks so much. > Brook > > --- On *Wed, 10/5/11, Nick Foster <nick@ettus.com>* wrote: > > > From: Nick Foster <nick@ettus.com> > Subject: Re: [Discuss-gnuradio] Intermediate frequency question > To: "Brook Lin" <gnu.fans@yahoo.com> > Date: Wednesday, October 5, 2011, 11:22 PM > > > By "no IF frequency" he meant the LO frequency is the same as the RF > frequency. This is called a zero-IF receiver, or direct conversion. > > http://en.wikipedia.org/wiki/Direct-conversion_receiver > > On Wed, Oct 5, 2011 at 4:20 PM, Brook Lin <gnu.fans@yahoo.com<http://mc/compose?to=gnu.fans@yahoo.com>> > wrote: > > > > Hi All, > > > > I am confused on this reply, posted on > > > http://old.nabble.com/Intermediate-frequency-question-td23514126.html#a32598120 > > > http://old.nabble.com/Intermediate-frequency-question-td23514126.html#a32598120 > > . The reply said that "With the RFX2400, and most of the high frequency > usrp > > daughtercards, > > there is no IF frequency". How is that possible? For RFX2400 the RF range > is > > from 2.3GHz to 2.9GHz, the ADC rate for USRP1 is 64MS/s. If there is no > IF > > frequency, the ADC rate is obviously too low. There must be RF front-end > on > > the daughterboard to tune the RF to the IF. Right? If so, my question is > > what the IF is? Obviously, f_IF = f_RF - f_LO. (1) Are we setting the > f_LO > > when we tune the usrp by usrp.tune(self.u, 0, self.subdev, target_freq)? > (2) > > How to figure out f_IF for different daughterboards? > > > > Thanks in advance, > > Brook > > -- > > View this message in context: > http://old.nabble.com/Re%3A-Intermediate-frequency-question-tp32598458p32598458.html > > Sent from the GnuRadio mailing list archive at Nabble.com. > > > > > > _______________________________________________ > > Discuss-gnuradio mailing list > > Discuss-gnuradio@gnu.org <http://mc/compose?to=Discuss-gnuradio@gnu.org> > > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > > >