Hello Eddie, I will try the same thing in a few weeks but using the USRP2 board. I hope your work is going great. Do you mind if I contact you for advice?
Greetings. Eduardo. 2011/6/24 Marcus D. Leech <mle...@ripnet.com> > ** > On 06/24/2011 03:03 AM, Eddie Sun wrote: > > Thanks for the reply, but i still have some questions. > > 2011/6/21 John Andrews <gnu.f...@gmail.com> > >> >> A USRP is a baseband IF receiver. Tune it to the GPS L1 frequency with the >> right decimation rate so that you have your band of interest selected. This >> should give you the IF signal. >> >> > The source block that i used is the "UHD:usrp_source block" for USRP N210 > in gniradio companion, after setting the frequency to L1 frequency > 1575.42MHz, there is no "decimation" term can be set in the block(only > usrp1_source and usrp2_source block have that term, not uhd), so should i > use the "Rational resampler" block to instead of it? or other method to > complete the decimation. > > The flow graph will only be > "UHD:usrp_source block"→"Rational resampler"→"File sink" > is that right? > > > And I'm still a little confused, why i don't need to down convert the > frequency but just do the decimation, i thought decimation is to slowdown > the sample rate. > > Is that mean the flow graph output from "UHD:usrp_source block" is already > a IF signal? If this is true, what is that signal frequency? It can't still > have the 1575.42MHz if it's a IF signal, isn't it? > > Thanks, > > Eddie > > In UHD, you set the sample-rate of the source block, not the > decimation. The UHD code determines the > appropriate decimation to use based on what it knows about the device. > > The USRP hardware "stack" arranges for the signal of interest to appear as > *complex baseband* signal, > in which the signal goes from -bandwidth/2 to +bandwidth/2, which uses > the "I" and "Q" signal > representation. The "IF" is 0Hz in this case. You shouldn't need to > re-sample to process the resulting > baseband signal. This baseband "I and Q" signal format is *extremely* > common in modern > DSP systems for RF. For more background, you should look up the terms > "direct conversion receiver", > and "quadrature mixer" on Google. > > -- > Principal Investigator > Shirleys Bay Radio Astronomy Consortiumhttp://www.sbrac.org > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > >
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