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

[nansai hu]

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.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)