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

From: Josh Blum
Subject: Re: [Discuss-gnuradio] How to modify freq deviation in a FM radio?????
Date: Tue, 27 Oct 2009 22:21:41 -0700
User-agent: Thunderbird (X11/20090817)

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.


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',
        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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