hello guys,
thank you Josh, Achilleas and Eric for the very precious help! 
I’ve been working upon your suggestions and what I did is:
file_source_bytewise=gr.file_source(gr.sizeof_char,
“/mnt/root/gnuradio_datastreams/1.MPG”)
file_chunker=gr.packed_to_unpacked_bb(2,1) #second argument is
endianness (??)
constellation=array((1+1j,1-1j,-1-1j,-1+1j),Complex)
print constellation
symbol_mapper=gr.chunks_to_symbols_bc(constellation, 1)
self.connect(file_source_bytewise,file_chunker,symbol_mapper)
self.connect(symbol_mapper,series_to_parallel,inverse_fft,parallel_to_series,gain,self.u)
which connected to an inverse fft and then sent out brings out the
attacched screenshot.
is the constellation mapping well done? (in terms of block usage I mean)
thanks for help and attention
vincenzo
ps
I’m trying to move as close as possible to ofdm with qpsk mapping on the
python level…