Re: [Discuss-gnuradio] How to modify freq deviation in a FM radio?????

[Josh Blum]

My advice is to get this all figured out in software before using any 
hardware (usrps and spectrum analyzers).

You can simulate the effect of changing the max deviation all in 
software using a noise source, throttle, nbfm tx block, and an fft sink 
(all in grc).

I guarantee that changing max deviation from 5 to 50k makes a big 
difference.

-Josh

nansai hu wrote:
> I want to design a FM radio with freq deviation can be change.
> Then I tried to modified an example in GNUradio example folder which name
> "fm_tx4.py" in line61,let max_dev=5 to 50K,shown in following yellow label.
> but there is no change at all in a spectrum analyzer.
> Help me,thanks
>
> class pipeline(gr.hier_block2):
>     def __init__(self, filename, lo_freq, audio_rate, if_rate):
>
>         gr.hier_block2.__init__(self, "pipeline",
>                                 gr.io_signature(0, 0, 0),
> # Input signature
>                                 gr.io_signature(1, 1, gr.sizeof_gr_complex))
> # Output signature
>
>         src = gr.file_source (gr.sizeof_float,'/home/sdr/Desktop/hu/1.wma',
> True)
>         fmtx = blks2.nbfm_tx (audio_rate, if_rate, max_dev=5, tau=75e-6)
>
>         # Local oscillator
>         lo = gr.sig_source_c (if_rate,        # sample rate
>                               gr.GR_SIN_WAVE, # waveform type
>                               lo_freq,        #frequency
>                               1.0,            # amplitude
>                               0)              # DC Offset
>         mixer = gr.multiply_cc ()
>
>         self.connect (src, fmtx, (mixer, 0))
>         self.connect (lo, (mixer, 1))
>         self.connect (mixer, self)
>
>
>
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