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
<address@hidden> 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!
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