tetra-demod.py launch problem

Hello, i am a newbie and i a just install osmo tetra under ubuntu 11.10 When i go : cd osmo-tetra cd src cd demod cd python and launch python tetra-demod.py This is the terminal answer gr_fir_ccc: using 3DNow!Ext sample rate: 195312 in.dat: No such file or directory Traceback (most recent call last):   File "tetra-demod.py", line 67, in <module>     my_top_block().run()   File "tetra-demod.py", line 45, in __init__     IN = gr.file_source(gr.sizeof_gr_complex, options.input_file)   File "/usr/local/lib/python2.7/dist-packages/gnuradio/gr/gnuradio_core_io.py", line 385, in file_source     return _gnuradio_core_io.file_source(*args, **kwargs) RuntimeError: can't open file What is the problem ? i can't continue with this files problems. Thank for your help.