On 25.05.2014 20:01, jason sam wrote:
> > But if it is doing FM then there should be some min and max
> > frequencies between which the signal will be switching?
>
If you refer to the source code of the frequency_modulator_fc_impl.cc, then
the min and max frequencies could be calculated.
Says, your sampling rate is samp_rate
Assuming the lowest input value to the FM block is zero, then
minimum frequency of the FM output = samp_rate * sensitivity / ( 2 * PI )
Assuming the highest input value to the FM block is Vmax, then
maximum frequency of the FM output = samp_rate * ( sensitivity + Vmax ) /
( 2 * PI)
For reference, the work function of the FM block is as below.
int
frequency_modulator_fc_impl::work( int noutput_items,
gr_vector_const_void_star &input_items,
gr_vector_void_star &output_items)
{
const float *in = (const float*)input_items[0];
gr_complex *out = (gr_complex*)output_items[0];
for(int i = 0; i < noutput_items; i++)
{
d_phase = d_phase + d_sensitivity * in[i];
while (d_phase > (float)(M_PI))
d_phase -= (float)(2.0 * M_PI);
while (d_phase < (float)(-M_PI))
d_phase += (float)(2.0 * M_PI);
float oi, oq;
gr_int32 angle = gr::fxpt::float_to_fixed (d_phase);
gr::fxpt::sincos(angle, &oq, &oi);
out[i] = gr_complex(oi, oq);
}
return noutput_items;
}
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