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Re: [Discuss-gnuradio] USRP2 FM TX and FM RX working together
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From: |
Nick Foster |
|
Subject: |
Re: [Discuss-gnuradio] USRP2 FM TX and FM RX working together |
|
Date: |
Wed, 22 Sep 2010 10:39:06 -0700 |
Jorge,
Your sample rates do not match. The sample rates your USRP2 is operating
at is fixed for a given decimation/interpolation, and you must choose
sample rates in your upstream and downstream blocks to match.
For instance, in your receiver chain, you are using a decimation rate of
64. This means that your USRP2 will provide samples to the rest of your
flowgraph at 1.5625Msps. This is connected to an FFT sink operating at
200ksps -- this is not correct. If you want to operate at 200ksps you
must provide a resampling block to get there. Likewise, your rational
resampler at (32/25) outputs a sample rate of (1.5625e6 * (32/25)) = 2e6
samples per second. Your low pass filter which follows is expecting a
sample rate of 256k. This will cause the filter coefficients to be
incorrectly calculated, and eventually will cause over/underruns when
you finally get to a block which operates at a fixed sample rate, like
your audio sink.
The "SSSSSSSSSSSS" you are seeing is caused by the audio sink being
overrun by providing it with 250ksps when it is expecting 32ksps.
Nick
On Wed, 2010-09-22 at 08:30 +0200, Jorge Miguel wrote:
> Sorry, in my previous email the code was corrupted.. This is the right
> code of my GRC:
>
> <?xml version='1.0' encoding='ASCII'?>
> <flow_graph>
> <timestamp>Wed Sep 22 08:14:26 2010</timestamp>
> <block>
> <key>variable_slider</key>
> <param>
> <key>id</key>
> <value>tune_filter</value>
> </param>
> <param>
> <key>_enabled</key>
> <value>True</value>
> </param>
> <param>
> <key>label</key>
> <value>LPF Cutoff Freq</value>
> </param>
> <param>
> <key>value</key>
> <value>75000</value>
> </param>
> <param>
> <key>min</key>
> <value>15000</value>
> </param>
> <param>
> <key>max</key>
> <value>150000</value>
> </param>
> <param>
> <key>num_steps</key>
> <value>1000</value>
> </param>
> <param>
> <key>style</key>
> <value>wx.SL_HORIZONTAL</value>
> </param>
> <param>
> <key>converver</key>
> <value>float_converter</value>
> </param>
> <param>
> <key>grid_pos</key>
> <value></value>
> </param>
> <param>
> <key>notebook</key>
> <value></value>
> </param>
> <param>
> <key>_coordinate</key>
> <value>(0, 127)</value>
> </param>
> <param>
> <key>_rotation</key>
> <value>0</value>
> </param>
> </block>
> <block>
> <key>gr_frequency_modulator_fc</key>
> <param>
> <key>id</key>
> <value>gr_frequency_modulator_fc_0</value>
> </param>
> <param>
> <key>_enabled</key>
> <value>True</value>
> </param>
> <param>
> <key>sensitivity</key>
> <value>0.980</value>
> </param>
> <param>
> <key>_coordinate</key>
> <value>(454, 315)</value>
> </param>
> <param>
> <key>_rotation</key>
> <value>0</value>
> </param>
> </block>
> <block>
> <key>blks2_rational_resampler_xxx</key>
> <param>
> <key>id</key>
> <value>blks2_rational_resampler_xxx_0_0</value>
> </param>
> <param>
> <key>_enabled</key>
> <value>True</value>
> </param>
> <param>
> <key>type</key>
> <value>fff</value>
> </param>
> <param>
> <key>decim</key>
> <value>1</value>
> </param>
> <param>
> <key>interp</key>
> <value>5</value>
> </param>
> <param>
> <key>taps</key>
> <value>[]</value>
> </param>
> <param>
> <key>fractional_bw</key>
> <value>0</value>
> </param>
> <param>
> <key>_coordinate</key>
> <value>(233, 68)</value>
> </param>
> <param>
> <key>_rotation</key>
> <value>0</value>
> </param>
> </block>
> <block>
> <key>note</key>
> <param>
> <key>id</key>
> <value>Chain1</value>
> </param>
> <param>
> <key>_enabled</key>
> <value>True</value>
> </param>
> <param>
> <key>note</key>
> <value>MODULATOR</value>
> </param>
> <param>
> <key>_coordinate</key>
> <value>(233, 9)</value>
> </param>
> <param>
> <key>_rotation</key>
> <value>0</value>
> </param>
> </block>
> <block>
> <key>note</key>
> <param>
> <key>id</key>
> <value>Chain1_0</value>
> </param>
> <param>
> <key>_enabled</key>
> <value>True</value>
> </param>
> <param>
> <key>note</key>
> <value>DEMODULATOR</value>
> </param>
> <param>
> <key>_coordinate</key>
> <value>(181, 427)</value>
> </param>
> <param>
> <key>_rotation</key>
> <value>0</value>
> </param>
> </block>
> <block>
> <key>blks2_rational_resampler_xxx</key>
> <param>
> <key>id</key>
> <value>blks2_rational_resampler_xxx_1</value>
> </param>
> <param>
> <key>_enabled</key>
> <value>True</value>
> </param>
> <param>
> <key>type</key>
> <value>fff</value>
> </param>
> <param>
> <key>decim</key>
> <value>1</value>
> </param>
> <param>
> <key>interp</key>
> <value>4</value>
> </param>
> <param>
> <key>taps</key>
> <value>[]</value>
> </param>
> <param>
> <key>fractional_bw</key>
> <value>0</value>
> </param>
> <param>
> <key>_coordinate</key>
> <value>(699, 122)</value>
> </param>
> <param>
> <key>_rotation</key>
> <value>0</value>
> </param>
> </block>
> <block>
> <key>wxgui_fftsink2</key>
> <param>
> <key>id</key>
> <value>wxgui_fftsink2_0_0</value>
> </param>
> <param>
> <key>_enabled</key>
> <value>True</value>
> </param>
> <param>
> <key>type</key>
> <value>complex</value>
> </param>
> <param>
> <key>title</key>
> <value>FFT Plot</value>
> </param>
> <param>
> <key>samp_rate</key>
> <value>200000</value>
> </param>
> <param>
> <key>baseband_freq</key>
> <value>2000000</value>
> </param>
> <param>
> <key>y_per_div</key>
> <value>10</value>
> </param>
> <param>
> <key>y_divs</key>
> <value>10</value>
> </param>
> <param>
> <key>ref_level</key>
> <value>50</value>
> </param>
> <param>
> <key>fft_size</key>
> <value>512</value>
> </param>
> <param>
> <key>fft_rate</key>
> <value>50</value>
> </param>
> <param>
> <key>peak_hold</key>
> <value>False</value>
> </param>
> <param>
> <key>average</key>
> <value>False</value>
> </param>
> <param>
> <key>avg_alpha</key>
> <value>0</value>
> </param>
> <param>
> <key>grid_pos</key>
> <value></value>
> </param>
> <param>
> <key>notebook</key>
> <value></value>
> </param>
> <param>
> <key>_coordinate</key>
> <value>(370, 568)</value>
> </param>
> <param>
> <key>_rotation</key>
> <value>0</value>
> </param>
> </block>
> <block>
> <key>audio_sink</key>
> <param>
> <key>id</key>
> <value>audio_sink_0</value>
> </param>
> <param>
> <key>_enabled</key>
> <value>True</value>
> </param>
> <param>
> <key>samp_rate</key>
> <value>32000</value>
> </param>
> <param>
> <key>device_name</key>
> <value>plughw:0,0</value>
> </param>
> <param>
> <key>ok_to_block</key>
> <value>True</value>
> </param>
> <param>
> <key>num_inputs</key>
> <value>1</value>
> </param>
> <param>
> <key>_coordinate</key>
> <value>(607, 648)</value>
> </param>
> <param>
> <key>_rotation</key>
> <value>0</value>
> </param>
> </block>
> <block>
> <key>usrp2_sink_xxxx</key>
> <param>
> <key>id</key>
> <value>usrp2_sink_xxxx_0</value>
> </param>
> <param>
> <key>_enabled</key>
> <value>True</value>
> </param>
> <param>
> <key>type</key>
> <value>complex</value>
> </param>
> <param>
> <key>interface</key>
> <value></value>
> </param>
> <param>
> <key>mac_addr</key>
> <value></value>
> </param>
> <param>
> <key>interpolation</key>
> <value>104</value>
> </param>
> <param>
> <key>frequency</key>
> <value>fm_freq_mod</value>
> </param>
> <param>
> <key>lo_offset</key>
> <value>float('inf')</value>
> </param>
> <param>
> <key>gain</key>
> <value>0</value>
> </param>
> <param>
> <key>_coordinate</key>
> <value>(874, 283)</value>
> </param>
> <param>
> <key>_rotation</key>
> <value>0</value>
> </param>
> </block>
> <block>
> <key>usrp2_source_xxxx</key>
> <param>
> <key>id</key>
> <value>usrp2_source_xxxx_0</value>
> </param>
> <param>
> <key>_enabled</key>
> <value>True</value>
> </param>
> <param>
> <key>type</key>
> <value>complex</value>
> </param>
> <param>
> <key>interface</key>
> <value></value>
> </param>
> <param>
> <key>mac_addr</key>
> <value></value>
> </param>
> <param>
> <key>decimation</key>
> <value>64</value>
> </param>
> <param>
> <key>frequency</key>
> <value>tune_osc_dem</value>
> </param>
> <param>
> <key>lo_offset</key>
> <value>float('inf')</value>
> </param>
> <param>
> <key>gain</key>
> <value>20</value>
> </param>
> <param>
> <key>_coordinate</key>
> <value>(162, 521)</value>
> </param>
> <param>
> <key>_rotation</key>
> <value>0</value>
> </param>
> </block>
> <block>
> <key>variable_slider</key>
> <param>
> <key>id</key>
> <value>fm_freq_mod</value>
> </param>
> <param>
> <key>_enabled</key>
> <value>True</value>
> </param>
> <param>
> <key>label</key>
> <value>FM frequency modulator</value>
> </param>
> <param>
> <key>value</key>
> <value>94000000</value>
> </param>
> <param>
> <key>min</key>
> <value>0</value>
> </param>
> <param>
> <key>max</key>
> <value>110000000</value>
> </param>
> <param>
> <key>num_steps</key>
> <value>300</value>
> </param>
> <param>
> <key>style</key>
> <value>wx.SL_HORIZONTAL</value>
> </param>
> <param>
> <key>converver</key>
> <value>float_converter</value>
> </param>
> <param>
> <key>grid_pos</key>
> <value></value>
> </param>
> <param>
> <key>notebook</key>
> <value></value>
> </param>
> <param>
> <key>_coordinate</key>
> <value>(0, 253)</value>
> </param>
> <param>
> <key>_rotation</key>
> <value>0</value>
> </param>
> </block>
> <block>
> <key>variable_slider</key>
> <param>
> <key>id</key>
> <value>tune_osc_dem</value>
> </param>
> <param>
> <key>_enabled</key>
> <value>True</value>
> </param>
> <param>
> <key>label</key>
> <value>Tunned frequency demodulator</value>
> </param>
> <param>
> <key>value</key>
> <value>94000000</value>
> </param>
> <param>
> <key>min</key>
> <value>88000000</value>
> </param>
> <param>
> <key>max</key>
> <value>108000000</value>
> </param>
> <param>
> <key>num_steps</key>
> <value>800</value>
> </param>
> <param>
> <key>style</key>
> <value>wx.SL_HORIZONTAL</value>
> </param>
> <param>
> <key>converver</key>
> <value>float_converter</value>
> </param>
> <param>
> <key>grid_pos</key>
> <value></value>
> </param>
> <param>
> <key>notebook</key>
> <value></value>
> </param>
> <param>
> <key>_coordinate</key>
> <value>(1, 1)</value>
> </param>
> <param>
> <key>_rotation</key>
> <value>0</value>
> </param>
> </block>
> <block>
> <key>gr_wavfile_source</key>
> <param>
> <key>id</key>
> <value>gr_wavfile_source_0</value>
> </param>
> <param>
> <key>_enabled</key>
> <value>True</value>
> </param>
> <param>
> <key>file</key>
> <value>/home/thales/Desktop/outfile2.wav</value>
> </param>
> <param>
> <key>repeat</key>
> <value>True</value>
> </param>
> <param>
> <key>nchan</key>
> <value>1</value>
> </param>
> <param>
> <key>_coordinate</key>
> <value>(223, 186)</value>
> </param>
> <param>
> <key>_rotation</key>
> <value>180</value>
> </param>
> </block>
> <block>
> <key>gr_multiply_const_vxx</key>
> <param>
> <key>id</key>
> <value>gr_multiply_const_vxx_1</value>
> </param>
> <param>
> <key>_enabled</key>
> <value>True</value>
> </param>
> <param>
> <key>type</key>
> <value>complex</value>
> </param>
> <param>
> <key>const</key>
> <value>32000</value>
> </param>
> <param>
> <key>vlen</key>
> <value>1</value>
> </param>
> <param>
> <key>_coordinate</key>
> <value>(645, 315)</value>
> </param>
> <param>
> <key>_rotation</key>
> <value>0</value>
> </param>
> </block>
> <block>
> <key>blks2_rational_resampler_xxx</key>
> <param>
> <key>id</key>
> <value>blks2_rational_resampler_xxx_1_0_0</value>
> </param>
> <param>
> <key>_enabled</key>
> <value>True</value>
> </param>
> <param>
> <key>type</key>
> <value>ccc</value>
> </param>
> <param>
> <key>decim</key>
> <value>25</value>
> </param>
> <param>
> <key>interp</key>
> <value>32</value>
> </param>
> <param>
> <key>taps</key>
> <value>[]</value>
> </param>
> <param>
> <key>fractional_bw</key>
> <value>0</value>
> </param>
> <param>
> <key>_coordinate</key>
> <value>(371, 467)</value>
> </param>
> <param>
> <key>_rotation</key>
> <value>0</value>
> </param>
> </block>
> <block>
> <key>low_pass_filter</key>
> <param>
> <key>id</key>
> <value>low_pass_filter_0</value>
> </param>
> <param>
> <key>_enabled</key>
> <value>True</value>
> </param>
> <param>
> <key>type</key>
> <value>fir_filter_ccf</value>
> </param>
> <param>
> <key>decim</key>
> <value>2</value>
> </param>
> <param>
> <key>interp</key>
> <value>1</value>
> </param>
> <param>
> <key>gain</key>
> <value>10</value>
> </param>
> <param>
> <key>samp_rate</key>
> <value>256000</value>
> </param>
> <param>
> <key>cutoff_freq</key>
> <value>tune_filter</value>
> </param>
> <param>
> <key>width</key>
> <value>5000</value>
> </param>
> <param>
> <key>window</key>
> <value>WIN_HAMMING</value>
> </param>
> <param>
> <key>beta</key>
> <value>6.76</value>
> </param>
> <param>
> <key>_coordinate</key>
> <value>(583, 443)</value>
> </param>
> <param>
> <key>_rotation</key>
> <value>0</value>
> </param>
> </block>
> <block>
> <key>blks2_fm_demod_cf</key>
> <param>
> <key>id</key>
> <value>blks2_fm_demod_cf_0</value>
> </param>
> <param>
> <key>_enabled</key>
> <value>True</value>
> </param>
> <param>
> <key>chan_rate</key>
> <value>128000</value>
> </param>
> <param>
> <key>audio_decim</key>
> <value>4</value>
> </param>
> <param>
> <key>deviation</key>
> <value>75000</value>
> </param>
> <param>
> <key>audio_pass</key>
> <value>1000</value>
> </param>
> <param>
> <key>audio_stop</key>
> <value>16000</value>
> </param>
> <param>
> <key>gain</key>
> <value>20.0</value>
> </param>
> <param>
> <key>tau</key>
> <value>75e-6</value>
> </param>
> <param>
> <key>_coordinate</key>
> <value>(784, 443)</value>
> </param>
> <param>
> <key>_rotation</key>
> <value>0</value>
> </param>
> </block>
> <block>
> <key>low_pass_filter</key>
> <param>
> <key>id</key>
> <value>low_pass_filter_0_0</value>
> </param>
> <param>
> <key>_enabled</key>
> <value>True</value>
> </param>
> <param>
> <key>type</key>
> <value>interp_fir_filter_fff</value>
> </param>
> <param>
> <key>decim</key>
> <value>1</value>
> </param>
> <param>
> <key>interp</key>
> <value>1</value>
> </param>
> <param>
> <key>gain</key>
> <value>1</value>
> </param>
> <param>
> <key>samp_rate</key>
> <value>160000</value>
> </param>
> <param>
> <key>cutoff_freq</key>
> <value>1.5e3</value>
> </param>
> <param>
> <key>width</key>
> <value>2e3</value>
> </param>
> <param>
> <key>window</key>
> <value>WIN_HAMMING</value>
> </param>
> <param>
> <key>beta</key>
> <value>6.76</value>
> </param>
> <param>
> <key>_coordinate</key>
> <value>(458, 44)</value>
> </param>
> <param>
> <key>_rotation</key>
> <value>0</value>
> </param>
> </block>
> <block>
> <key>options</key>
> <param>
> <key>id</key>
> <value>top_block</value>
> </param>
> <param>
> <key>_enabled</key>
> <value>True</value>
> </param>
> <param>
> <key>title</key>
> <value></value>
> </param>
> <param>
> <key>author</key>
> <value></value>
> </param>
> <param>
> <key>description</key>
> <value></value>
> </param>
> <param>
> <key>window_size</key>
> <value>1280, 1024</value>
> </param>
> <param>
> <key>generate_options</key>
> <value>wx_gui</value>
> </param>
> <param>
> <key>category</key>
> <value>Custom</value>
> </param>
> <param>
> <key>run</key>
> <value>True</value>
> </param>
> <param>
> <key>realtime_scheduling</key>
> <value></value>
> </param>
> <param>
> <key>_coordinate</key>
> <value>(2, 384)</value>
> </param>
> <param>
> <key>_rotation</key>
> <value>0</value>
> </param>
> </block>
> <connection>
> <source_block_id>low_pass_filter_0_0</source_block_id>
> <sink_block_id>blks2_rational_resampler_xxx_1</sink_block_id>
> <source_key>0</source_key>
> <sink_key>0</sink_key>
> </connection>
> <connection>
>
> <source_block_id>blks2_rational_resampler_xxx_0_0</source_block_id>
> <sink_block_id>low_pass_filter_0_0</sink_block_id>
> <source_key>0</source_key>
> <sink_key>0</sink_key>
> </connection>
> <connection>
> <source_block_id>blks2_rational_resampler_xxx_1</source_block_id>
> <sink_block_id>gr_frequency_modulator_fc_0</sink_block_id>
> <source_key>0</source_key>
> <sink_key>0</sink_key>
> </connection>
> <connection>
> <source_block_id>gr_frequency_modulator_fc_0</source_block_id>
> <sink_block_id>gr_multiply_const_vxx_1</sink_block_id>
> <source_key>0</source_key>
> <sink_key>0</sink_key>
> </connection>
> <connection>
> <source_block_id>gr_multiply_const_vxx_1</source_block_id>
> <sink_block_id>usrp2_sink_xxxx_0</sink_block_id>
> <source_key>0</source_key>
> <sink_key>0</sink_key>
> </connection>
> <connection>
> <source_block_id>gr_wavfile_source_0</source_block_id>
> <sink_block_id>blks2_rational_resampler_xxx_0_0</sink_block_id>
> <source_key>0</source_key>
> <sink_key>0</sink_key>
> </connection>
> <connection>
> <source_block_id>usrp2_source_xxxx_0</source_block_id>
> <sink_block_id>blks2_rational_resampler_xxx_1_0_0</sink_block_id>
> <source_key>0</source_key>
> <sink_key>0</sink_key>
> </connection>
> <connection>
> <source_block_id>usrp2_source_xxxx_0</source_block_id>
> <sink_block_id>wxgui_fftsink2_0_0</sink_block_id>
> <source_key>0</source_key>
> <sink_key>0</sink_key>
> </connection>
> <connection>
> <source_block_id>blks2_fm_demod_cf_0</source_block_id>
> <sink_block_id>audio_sink_0</sink_block_id>
> <source_key>0</source_key>
> <sink_key>0</sink_key>
> </connection>
> <connection>
>
> <source_block_id>blks2_rational_resampler_xxx_1_0_0</source_block_id>
> <sink_block_id>low_pass_filter_0</sink_block_id>
> <source_key>0</source_key>
> <sink_key>0</sink_key>
> </connection>
> <connection>
> <source_block_id>low_pass_filter_0</source_block_id>
> <sink_block_id>blks2_fm_demod_cf_0</sink_block_id>
> <source_key>0</source_key>
> <sink_key>0</sink_key>
> </connection>
> </flow_graph>
>
> On 21 September 2010 18:59, Rafael Diniz <address@hidden> wrote:
> Hi Jorge,
> Can you copy the .grc file you created?
>
>
> > Hello community!
> >
> > I initiated myself in GNU radio two weeks ago and I am
> learning as fast as
> > I
> > can. To begin with, I decided to play with GRC and my URSP2.
> > I successfully built a FM modulator that works fine.
> > I successfully built a FM demodulator that works fine.
> > But there are still several things I do not understand.
> >
> > While building the FM modulator:
> > 1)Wave file source
> > 2)Rational resampler
> > 3)LPF
> > 4)Rational resampler
> > 5)Frequency Mod
> > 6)Multiply const
> > 7)USRP2 sink
> >
> > Why is block 6 necessary? I tried with lots of values over 2
> and all of
> > them
> > are ok. I realized that the smaller the number, the higher
> the noise in my
> > receiver (my mobile phone). Is it related to the amplitude
> of the
> > modulated
> > signal?
> >
> > Another thing very strange is that if I create a GRC file
> with both,
> > transmitter and receiver with exactly the same blocks and
> the same
> > parameters I cannot hear any demodulated signal. I can see
> information
> > with
> > a FFT block connected to the receiver chain, and I am able
> to demodulate
> > the
> > signal with my mobile phone when the example is running but
> in my computer
> > I
> > do not hear anything else besides noise mixed with some sort
> of
> > non-understandable signal. Thus, I guess I have to change
> something in the
> > receiver chain although it works alone in my FM demodulator.
> I changed
> > every
> > single parameter but I cannot get any improvement.
> >
> > Any suggestions?
> >
> > Many thanks in advance,
> > Jorge.
>
>
>
>
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