Re: [Discuss-gnuradio] bell 202 modulation

[Eric Blossom]

On Wed, Mar 29, 2006 at 10:07:21PM +0200, Matteo Campanella wrote:
> yep, my fault to use the wrong name for it :-)
> I am indeed working on the bits to symbol (nrzi) block right now, and
> later on I am willing to do the HDLC block with flag, FCS and bit stuffing
> in order to put up the following chain:
> 
> message_source->hdlc->nrzi->modulation->duc
> 
> right now i am stuck at modulation, that is, to find a method to use the
> frequency modulator to do that at baseband, as suggested from Eric...
> 
> 73, Matteo iz2eeq

A few more hints:

The sensitivity argument of the gr.frequency_modulator_fc is in
radians/sample/<input-units>.  If your input data is +/- 1, then you
can produce two tones symmetrically around zero.  Remember that this
is complex and hence -freq is distinguishable from +freq.  Then just
translate the baseband up to the center frequency you like by
multiplying by a complex sinusoid (or let the usrp duc handle it).

Eric