Challenge 1

Add a Frequency Sink of your own, then look at a square wave in the frequency domain.

Author Marc
Category GR World Challenges
Blocks 8
Connections 2
File _gnuradio-world-challenges/challenge_1.grc

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Blocks used

Block	Module	Used
Note	`GNU Radio`	2
Challenge	`GNU Radio`	1
GUI Layout	`GNU Radio`	1
QT GUI Time Sink	`GNU Radio`	1
Signal Source	`GNU Radio`	1
Throttle	`GNU Radio`	1
Variable	`GNU Radio`	1

Notes in this flowgraph

A Time Sink shows a signal as amplitude against time. The other half of DSP is the frequency domain: the same samples, drawn as how much energy sits at each frequency. GNU Radio has a sink for that too -- the QT GUI Frequency Sink.
Challenge: 1) Find "QT GUI Frequency Sink" in the block palette on the left and drag it onto the canvas. 2) Set its Type to Float (note the Down button is a shortcut). Our samples are real, not complex, and a Complex input port will refuse to connect to a Float stream. 3) Connect the Throttle's output to it: click the output port, then the sink's input port. A stream can feed more than one sink 4) Run it. The 1 kHz cosine is a single spike 5) Stop, then change the Signal Source waveform to Square. A square wave is a sum of odd harmonics: spikes at 3 kHz, 5 kHz, 7 kHz ... each smaller than the last

Flowgraph source

_gnuradio-world-challenges/challenge_1.grc

options:
    parameters:
        author: Marc
        comment: ''
        copyright: ''
        description: Add a Frequency Sink of your own, then look at a square wave in the frequency domain.
        generate_options: qt_gui
        id: Challenge_1
        title: Challenge 1
    states:
        coordinate: [10, 10]
        rotation: 0
        state: enabled
blocks:
-   name: samp_rate
    id: variable
    parameters:
        comment: ''
        value: '32000'
    states:
        coordinate: [330, 30]
        rotation: 0
        state: enabled
-   name: challenge_1
    id: wasm_challenge
    parameters:
        affinity: ''
        alias: ''
        challenge_id: challenge_1
        comment: ''
        criteria: "[\n {\"kind\": \"block_present\", \"id\": \"qtgui_freq_sink_x\", \"goal\": \"Add a QT GUI Frequency Sink and connect the Throttle to it\"},\n {\"kind\": \"ran\", \"seconds\": 4, \"goal\": \"Run it: one cosine is one spike in the frequency domain\"},\n {\"kind\": \"param\", \"block\": \"tone\", \"param\": \"waveform\", \"matches\": \"SQR\", \"goal\": \"Switch the Signal Source to a square wave and find its harmonics\"}\n]"
        requires: challenge_0
        title: Into the frequency domain
    states:
        coordinate: [500, 10]
        rotation: 0
        state: enabled
-   name: gui_layout
    id: wasm_gui_layout
    parameters:
        affinity: ''
        alias: ''
        columns: '12'
        comment: ''
        layout: '{"time_sink":[0,0,12,5]}'
        row_height: '60'
    states:
        coordinate: [1410, 10]
        rotation: 0
        state: enabled
-   name: note_0
    id: note
    parameters:
        affinity: ''
        alias: ''
        bgcolor: '#4dff6a'
        comment: ''
        note: 'A Time Sink shows a signal as amplitude against time. The other half of DSP is the frequency domain: the same samples, drawn as how much energy sits at each frequency. GNU Radio has a sink for that too -- the QT GUI Frequency Sink.'
    states:
        coordinate: [980, 70]
        rotation: 0
        state: enabled
-   name: note_1
    id: note
    parameters:
        affinity: ''
        alias: ''
        bgcolor: '#4dff6a'
        comment: ''
        note: "Challenge:\n1) Find \"QT GUI Frequency Sink\" in the block palette on the left and drag it onto the canvas.\n2) Set its Type to Float (note the Down button is a shortcut). Our samples are real, not complex, and a Complex input port will refuse to connect to a Float stream.\n3) Connect the Throttle's output to it: click the output port, then the sink's input port. A stream can feed more than one sink\n4) Run it. The 1 kHz cosine is a single spike\n5) Stop, then change the Signal Source waveform to Square. A square wave is a sum of odd harmonics: spikes at 3 kHz, 5 kHz, 7 kHz ... each smaller than the last"
    states:
        coordinate: [30, 160]
        rotation: 0
        state: enabled
-   name: throttle
    id: blocks_throttle2
    parameters:
        affinity: ''
        alias: ''
        comment: "Limits the rate of samples\nflowing through"
        ignoretag: 'True'
        limit: auto
        maximum: '0.1'
        maxoutbuf: '0'
        minoutbuf: '0'
        samples_per_second: samp_rate
        type: float
        vlen: '1'
    states:
        coordinate: [810, 250]
        rotation: 0
        state: enabled
-   name: time_sink
    id: qtgui_time_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'
        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: The time domain
        ctrlpanel: 'False'
        entags: 'True'
        grid: 'False'
        label1: Signal 1
        label10: Signal 10
        label2: Signal 2
        label3: Signal 3
        label4: Signal 4
        label5: Signal 5
        label6: Signal 6
        label7: Signal 7
        label8: Signal 8
        label9: Signal 9
        legend: 'True'
        marker1: '-1'
        marker10: '-1'
        marker2: '-1'
        marker3: '-1'
        marker4: '-1'
        marker5: '-1'
        marker6: '-1'
        marker7: '-1'
        marker8: '-1'
        marker9: '-1'
        name: Time domain
        nconnections: '1'
        size: '512'
        srate: samp_rate
        stemplot: 'False'
        style1: '1'
        style10: '1'
        style2: '1'
        style3: '1'
        style4: '1'
        style5: '1'
        style6: '1'
        style7: '1'
        style8: '1'
        style9: '1'
        tr_chan: '0'
        tr_delay: '0'
        tr_level: '0'
        tr_mode: qtgui.TRIG_MODE_FREE
        tr_slope: qtgui.TRIG_SLOPE_POS
        tr_tag: ''
        type: float
        update_time: '0.1'
        width1: '1'
        width10: '1'
        width2: '1'
        width3: '1'
        width4: '1'
        width5: '1'
        width6: '1'
        width7: '1'
        width8: '1'
        width9: '1'
        ylabel: Amplitude
        ymax: '1'
        ymin: '-1'
        yunit: ''
    states:
        coordinate: [1140, 250]
        rotation: 0
        state: enabled
-   name: tone
    id: analog_sig_source_x
    parameters:
        affinity: ''
        alias: ''
        amp: '0.5'
        comment: A 1 kHz tone
        freq: '1000'
        maxoutbuf: '0'
        minoutbuf: '0'
        offset: '0'
        phase: '0'
        samp_rate: samp_rate
        type: float
        waveform: analog.GR_SQR_WAVE
    states:
        coordinate: [460, 230]
        rotation: 0
        state: enabled
connections:
- [throttle, '0', time_sink, '0']
- [tone, '0', throttle, '0']
metadata:
    file_format: 1
    grc_version: 3.11.0.0