Re: [Discuss-gnuradio] FSK modulation

[Tom Rondeau]

On Mon, Sep 10, 2012 at 5:50 PM, Joana Goncalves <address@hidden> wrote:
> Hello,
>
> I am quite new in GnuRadio Companion and I am just trying to transmit and
> receive a file through FSK modulation, but I am having some troubles.
>
> Attached is the block diagram that I am trying to implement. Do you know
> what is the problem here?
>
> I don’t understand very well some block and how they work, such as the
> Chunks to symbols and Interpolating FIR FILTER. Can you give me a help?
>
>
>
> Thank you very much for your help.
>
> Best regards
> Joana


Joana,

The chunks_to_symbols is a mapping block. It takes in a byte and
converts that to the set of symbols defined by the block. Basically,
the block takes in as its 'Symbol Table' argument a vector of complex
numbers, call this sym_table. The input stream to this block will be
bytes, and those bytes are mapped to the complex symbols in sym_table
directly. So if the input value is 0, the output is sym_table[0]; if
the input is 3, the output is sym_table[3]. That also means that your
symbol table should be as large as the input value "chunks" are
expected to be.

The interpolating filter is a rate conversion filter. It interpolates
a signal and then filters it to remove the images generated from the
filtering. You definitely don't want the taps of the filter to be all
1's; that won't filter out anything. You can use the 'gr.firdes' or
'gr.optfir' modules to build the filters for you. Remember that when
building a filter for the interpolator, make sure you specify the
sample rate as the sample rate /after/ the interpolation.

Tom