Re: [Discuss-gnuradio] fm modulation

[Alexandru Csete]

My guess is that the sample rates are messed up. Your signal source
uses 6.4 ksps and the USRP interpolation rate is set to 200. This will
give 1.28 Msps but you need to go up to 128 Msps. If I remember well
the highest interpolation USRP can have is 512, which gives 250 ksps
sample rate.

Under examples/usrp/ you can find several examples for FM transmitters
using the higher level NBFM modulator block. This block can already do
interpolation from audio rates to > 250 ksps required by USRP.

PS: Maybe you can attach the .grc file next time instead of the
generated python code.

Alex

On 13 July 2010 14:23, EsserIHF <address@hidden> wrote:
>
> Hi,
> I am trying to build a simple FM transmitter. The signal should be send by
> the USRP to an Spectrum Analyzer. I connected the Daughterboard BasicTX
> (TX_A) to a Spectrum Analyzer, but I didn't see the expected Spectrum.
> I used the Frequency Mod Block in grc. I think this Block should modulate
> the signal and the USRP send it out on 12,8 MHz. I hope you can help me
> building a graph who do this simple task of frequency modulation. I also
> tried the example on this website
> http://www.opendigitalradio.org/index.php/Simple_FM_transmitter_using_gnuradio
> , but on the spectrum analyzer i also didn't see the expected values.
>
>
> from gnuradio import gr
> from gnuradio.eng_option import eng_option
> from grc_gnuradio import usrp as grc_usrp
> from grc_gnuradio import wxgui as grc_wxgui
> from optparse import OptionParser
> import wx
>
> class top_block(grc_wxgui.top_block_gui):
>
>        def __init__(self):
>                grc_wxgui.top_block_gui.__init__(self, title="Top Block")
>
>                ##################################################
>                # Variables
>                ##################################################
>                self.samp_rate = samp_rate = 32000
>
>                ##################################################
>                # Blocks
>                ##################################################
>                self.gr_frequency_modulator_fc_0 = gr.frequency_modulator_fc(3)
>                self.gr_multiply_const_vxx_0 = gr.multiply_const_vcc((100, ))
>                self.gr_multiply_const_vxx_1 = gr.multiply_const_vff((10, ))
>                self.gr_sig_source_x_0_0 = gr.sig_source_f(6400, 
> gr.GR_CONST_WAVE, 3200,
> 1, 0)
>                self.usrp_simple_sink_x_0 = grc_usrp.simple_sink_c(which=0, 
> side="A")
>                self.usrp_simple_sink_x_0.set_interp_rate(200)
>                self.usrp_simple_sink_x_0.set_frequency(12800000, verbose=True)
>                self.usrp_simple_sink_x_0.set_gain(0)
>
>                ##################################################
>                # Connections
>                ##################################################
>                self.connect((self.gr_frequency_modulator_fc_0, 0),
> (self.gr_multiply_const_vxx_0, 0))
>                self.connect((self.gr_sig_source_x_0_0, 0), 
> (self.gr_multiply_const_vxx_1,
> 0))
>                self.connect((self.gr_multiply_const_vxx_1, 0),
> (self.gr_frequency_modulator_fc_0, 0))
>                self.connect((self.gr_multiply_const_vxx_0, 0),
> (self.usrp_simple_sink_x_0, 0))
>
>        def set_samp_rate(self, samp_rate):
>                self.samp_rate = samp_rate
>
> if __name__ == '__main__':
>        parser = OptionParser(option_class=eng_option, usage="%prog: 
> [options]")
>        (options, args) = parser.parse_args()
>        tb = top_block()
>        tb.Run(True)
>
> --
> View this message in context: 
> http://old.nabble.com/fm-modulation-tp29149390p29149390.html
> Sent from the GnuRadio mailing list archive at Nabble.com.
>
>
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