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 >
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