PySDR: Windowing, FFT Size, and the Waterfall

Companion to the Frequency Domain chapter of PySDR

Author Marc
Category Analog
Blocks 14
Connections 6
File analog/frequency_domain_windowing.grc

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Blocks used

Block	Module	Used
QT GUI Range	`GNU Radio`	4
Signal Source	`GNU Radio`	2
Add	`GNU Radio`	1
GUI Layout	`GNU Radio`	1
Noise Source	`GNU Radio`	1
Note	`GNU Radio`	1
QT GUI Frequency Sink	`GNU Radio`	1
QT GUI Waterfall Sink	`GNU Radio`	1
Throttle	`GNU Radio`	1
Variable	`GNU Radio`	1

Notes in this flowgraph

Two tones, one of them much weaker. Slide them together and watch the point where the FFT stops resolving them as two The sidelobes of the strong tone's window are what buries the weak one. Raise the FFT Size on the Frequency Sink to narrow each bin and the two separate sooner

Flowgraph source

analog/frequency_domain_windowing.grc

options:
    parameters:
        author: Marc
        comment: ''
        copyright: ''
        description: Companion to the Frequency Domain chapter of PySDR
        generate_options: qt_gui
        id: PySDR__Windowing__FFT_Size__and_the_Waterfall
        title: 'PySDR: Windowing, FFT Size, and the Waterfall'
    states:
        coordinate: [10, 10]
        rotation: 0
        state: enabled
blocks:
-   name: noise_amp
    id: variable_qtgui_range
    parameters:
        comment: ''
        label: Noise amplitude
        min_len: '200'
        orient: QtCore.Qt.Horizontal
        rangeType: float
        start: '0'
        step: '0.001'
        stop: '0.05'
        value: '0.001'
        widget: counter_slider
    states:
        coordinate: [350, 490]
        rotation: 0
        state: enabled
-   name: samp_rate
    id: variable
    parameters:
        comment: ''
        value: '100000'
    states:
        coordinate: [80, 140]
        rotation: 0
        state: enabled
-   name: strong_freq
    id: variable_qtgui_range
    parameters:
        comment: ''
        label: Strong tone (Hz)
        min_len: '200'
        orient: QtCore.Qt.Horizontal
        rangeType: float
        start: '-40000'
        step: '500'
        stop: '40000'
        value: '10000'
        widget: counter_slider
    states:
        coordinate: [780, 10]
        rotation: 0
        state: enabled
-   name: weak_amp
    id: variable_qtgui_range
    parameters:
        comment: ''
        label: Weak tone amplitude
        min_len: '200'
        orient: QtCore.Qt.Horizontal
        rangeType: float
        start: '0.0001'
        step: '0.0001'
        stop: '0.1'
        value: '0.003'
        widget: counter_slider
    states:
        coordinate: [1280, 10]
        rotation: 0
        state: enabled
-   name: weak_freq
    id: variable_qtgui_range
    parameters:
        comment: ''
        label: Weak tone (Hz)
        min_len: '200'
        orient: QtCore.Qt.Horizontal
        rangeType: float
        start: '-40000'
        step: '500'
        stop: '40000'
        value: '12000'
        widget: counter_slider
    states:
        coordinate: [1030, 10]
        rotation: 0
        state: enabled
-   name: add
    id: blocks_add_xx
    parameters:
        affinity: ''
        alias: ''
        comment: ''
        maxoutbuf: '0'
        minoutbuf: '0'
        num_inputs: '3'
        type: complex
        vlen: '1'
    states:
        coordinate: [340, 280]
        rotation: 0
        state: enabled
-   name: freq_sink
    id: qtgui_freq_sink_x
    parameters:
        affinity: ''
        alias: ''
        alpha1: '1'
        alpha10: '1'
        alpha2: '1'
        alpha3: '1'
        alpha4: '1'
        alpha5: '1'
        alpha6: '1'
        alpha7: '1'
        alpha8: '1'
        alpha9: '1'
        autoscale: 'False'
        average: '0.1'
        axislabels: 'True'
        color1: '"blue"'
        color10: '"dark blue"'
        color2: '"red"'
        color3: '"green"'
        color4: '"black"'
        color5: '"cyan"'
        color6: '"magenta"'
        color7: '"yellow"'
        color8: '"dark red"'
        color9: '"dark green"'
        comment: ''
        ctrlpanel: 'False'
        fc: '0'
        fftsize: '1024'
        grid: 'True'
        label1: ''
        label10: ''
        label2: ''
        label3: ''
        label4: ''
        label5: ''
        label6: ''
        label7: ''
        label8: ''
        label9: ''
        legend: 'True'
        marker1: '-1'
        marker10: '-1'
        marker2: '-1'
        marker3: '-1'
        marker4: '-1'
        marker5: '-1'
        marker6: '-1'
        marker7: '-1'
        marker8: '-1'
        marker9: '-1'
        maxoutbuf: '0'
        minoutbuf: '0'
        name: Spectrum
        nconnections: '1'
        samp_rate: samp_rate
        style1: '1'
        style10: '1'
        style2: '1'
        style3: '1'
        style4: '1'
        style5: '1'
        style6: '1'
        style7: '1'
        style8: '1'
        style9: '1'
        tr_chan: '0'
        tr_level: '0'
        tr_mode: qtgui.TRIG_MODE_FREE
        tr_tag: ''
        update_time: '0.1'
        width1: '1'
        width10: '1'
        width2: '1'
        width3: '1'
        width4: '1'
        width5: '1'
        width6: '1'
        width7: '1'
        width8: '1'
        width9: '1'
        ymax: '10'
        ymin: '-140'
    states:
        coordinate: [920, 280]
        rotation: 0
        state: enabled
-   name: noise
    id: analog_noise_source_x
    parameters:
        affinity: ''
        alias: ''
        amplitude: noise_amp
        comment: ''
        maxoutbuf: '0'
        minoutbuf: '0'
        seed: '0'
        type: complex
    states:
        coordinate: [90, 540]
        rotation: 0
        state: enabled
-   name: note_two
    id: note
    parameters:
        affinity: ''
        alias: ''
        comment: ''
        note: "Two tones, one of them much weaker. Slide them together and watch the point where the FFT stops resolving them as two\n\nThe sidelobes of the strong tone's window are what buries the weak one. Raise the FFT Size on the Frequency Sink to narrow each bin and the two separate sooner"
    states:
        coordinate: [330, 30]
        rotation: 0
        state: enabled
-   name: strong_tone
    id: analog_sig_source_x
    parameters:
        affinity: ''
        alias: ''
        amplitude: '1'
        comment: ''
        frequency: strong_freq
        maxoutbuf: '0'
        minoutbuf: '0'
        samp_rate: samp_rate
        type: complex
        waveform: analog.GR_COS_WAVE
    states:
        coordinate: [20, 260]
        rotation: 0
        state: enabled
-   name: throttle
    id: blocks_throttle2
    parameters:
        affinity: ''
        alias: ''
        comment: ''
        ignoretag: 'True'
        limit: auto
        maximum: '0.1'
        maxoutbuf: '0'
        minoutbuf: '0'
        samples_per_second: samp_rate
        type: complex
        vlen: '1'
    states:
        coordinate: [580, 290]
        rotation: 0
        state: enabled
-   name: wasm_gui_layout_0
    id: wasm_gui_layout
    parameters:
        affinity: ''
        alias: ''
        columns: '12'
        comment: ''
        layout: '{"freq_sink":[0,3,12,4],"noise_amp":[0,0,12,1],"strong_freq":[0,1,12,1],"waterfall_sink":[0,7,12,4],"weak_amp":[6,2,6,1],"weak_freq":[0,2,6,1]}'
        row_height: '60'
    states:
        coordinate: [1240, 230]
        rotation: 0
        state: enabled
-   name: waterfall_sink
    id: qtgui_waterfall_sink_x
    parameters:
        affinity: ''
        alias: ''
        alpha1: '1'
        alpha10: '1'
        alpha2: '1'
        alpha3: '1'
        alpha4: '1'
        alpha5: '1'
        alpha6: '1'
        alpha7: '1'
        alpha8: '1'
        alpha9: '1'
        axislabels: 'True'
        color1: '0'
        color10: '0'
        color2: '0'
        color3: '0'
        color4: '0'
        color5: '0'
        color6: '0'
        color7: '0'
        color8: '0'
        color9: '0'
        comment: ''
        fc: '0'
        fftsize: '1024'
        grid: 'False'
        int_max: '0'
        int_min: '-140'
        label1: ''
        label10: ''
        label2: ''
        label3: ''
        label4: ''
        label5: ''
        label6: ''
        label7: ''
        label8: ''
        label9: ''
        legend: 'True'
        maxoutbuf: '0'
        minoutbuf: '0'
        name: Waterfall
        nconnections: '1'
        samp_rate: samp_rate
        update_time: '0.1'
    states:
        coordinate: [920, 440]
        rotation: 0
        state: enabled
-   name: weak_tone
    id: analog_sig_source_x
    parameters:
        affinity: ''
        alias: ''
        amplitude: weak_amp
        comment: ''
        frequency: weak_freq
        maxoutbuf: '0'
        minoutbuf: '0'
        samp_rate: samp_rate
        type: complex
        waveform: analog.GR_COS_WAVE
    states:
        coordinate: [20, 400]
        rotation: 0
        state: enabled
connections:
- [add, '0', throttle, '0']
- [noise, '0', add, '2']
- [strong_tone, '0', add, '0']
- [throttle, '0', freq_sink, '0']
- [throttle, '0', waterfall_sink, '0']
- [weak_tone, '0', add, '1']
metadata:
    file_format: 1
    grc_version: 3.11.0.0