How to modify freq deviation in a FM radio?

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)

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

Yes,this seems work.but the intention is get a radio.So, I use a USRP
source
instead FFT sink and observe in Spectrum Analyzer and it still doesn’t
work.

I think the only different is I use a usrp as CF to put baseband FM
signal
to RF because Spectrum Analyzer quite like FFT sink.

2009/10/28 Josh B. [email protected]

Agilent4440
RBW=3Hz
span=1Mhz
center freq= USRP freq

2009/10/28 Josh B. [email protected]

nansai hu wrote:

Yes,this seems work.but the intention is get a radio.So, I use a USRP source
instead FFT sink and observe in Spectrum Analyzer and it still doesn’t work.

I think the only different is I use a usrp as CF to put baseband FM signal
to RF because Spectrum Analyzer quite like FFT sink.

Whats the resolution bandwidth on your spectrum analyzer set to? Perhaps
its not set fine/small enough?

-Josh