Hey Mahboob, Maybe take a look at the gr_mpsk_receiver block source for reference, that implements a Costas Loop with provision for constant frequency offset (theta). Anyway processing block it is, good luck!
John On Mon, Aug 2, 2010 at 3:47 PM, Rahman, Muhammad Mahboob Ur < mahboob-rah...@uiowa.edu> wrote: > Hi John, > > I have to implement a modified version of costas loop which is to be > used to compensate for frequency offset present between LO's of two USRP's > (RFX900). So, I think I should make a new such signal processing block now. > > Thanks, > Mahboob > > ------------------------------ > *From:* John Wilson [johnmwilso...@gmail.com] > *Sent:* 02 August 2010 02:33 > *To:* Rahman, Muhammad Mahboob Ur > *Cc:* discuss-gnuradio > *Subject:* Re: [Discuss-gnuradio] PLL and VCO questions > > Hey, > > You can't make a feedback system in the Python flowgraph. You can, however > use feedback in an individual signal processing block. If you need to use a > PLL look at the Costas loop block which locks to RF signals with complex > baseband components eg. QPSK, SSB etc. > > John > > > On Mon, Aug 2, 2010 at 2:52 AM, Rahman, Muhammad Mahboob Ur < > mahboob-rah...@uiowa.edu> wrote: > >> Hi all, >> >> I have made up a simple PLL block in GRC using a multiplier phase >> detector, low pass filter (FIR) and VCO to lock to a 1KHz reference. When I >> run the simulation, it gives me a run time error "flow graph has loops!". >> Does it mean that I cannot make any kind of feedback system in the gnuradio >> or is there something else to ponder? Also, I am adding "1" to the output of >> the low pass filter so that when the phase error (output of low pass filter) >> becomes zero in the locked state, the VCO then runs at its quiescent >> frequency of 1KHz (I have set the sensitivity of VCO as 2*pi*1K rad/s/V). Is >> it the right way to use VCO? >> >> Below is the error message: >> >> ------------------------------------------------------ >> ------------------------------------------------------ >> >> Generating: "/home/mahboob/Desktop/top_block.py" >> >> Executing: "/home/mahboob/Desktop/top_block.py" >> >> >>> gr_fir_fff: using SSE >> Traceback (most recent call last): >> File "/home/mahboob/Desktop/top_block.py", line 71, in <module> >> tb.Run(True) >> File >> "/usr/lib/python2.6/dist-packages/grc_gnuradio/wxgui/top_block_gui.py", line >> 73, in Run >> if start: self.start() >> File "/usr/lib/python2.6/dist-packages/gnuradio/gr/top_block.py", line >> 97, in start >> self._tb.start() >> File >> "/usr/lib/python2.6/dist-packages/gnuradio/gr/gnuradio_swig_py_runtime.py", >> line 1455, in start >> return _gnuradio_swig_py_runtime.gr_top_block_sptr_start(self) >> RuntimeError: flow graph has loops! >> _______________________________________________ >> Discuss-gnuradio mailing list >> Discuss-gnuradio@gnu.org >> http://lists.gnu.org/mailman/listinfo/discuss-gnuradio >> > >
_______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
