Re: [Discuss-gnuradio] bell 202 modulation

[Eric Blossom]

On Tue, Mar 28, 2006 at 11:51:03PM +0200, Matteo Campanella wrote:
> Hello, I am trying to find the best way to implement a bell 202 modem in
> gnuradio. The problem I am facing is that I need to produce two tones, one
> for mark and one for space, and I have to switch from one to other
> depending on which symbol I am sending. The duration of the tone (or tone
> switch) must be set exactly according to the baud rate of 1200 I have to
> produce.
> 
> I was thinking to use the nco class to generate the tones, and to output n
> samples per symbol at a certain fixed sample rate that would be enough for
> the 1200 baud, let´s say the standard audio 48000.
> 
> Has anyone better suggestions to work this out?
> 
> MC

Use the gr.frequency_modulator_fc block to generate complex baseband FSK.

You'll probably want to use gr.bytes_to_syms to in front of it, or in
the more general case: gr.packed_to_unpacked followed by
gr_chunks_to_symbols_bf.

Eric