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| hambasics:sections:wavemodulation [2022/11/04 18:52] – created - external edit 127.0.0.1 | hambasics:sections:wavemodulation [2026/04/01 20:47] (current) – [FM] va7fi |
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| ===== Amplitude, Wavelength, Frequency, and Period ===== | ===== Amplitude, Wavelength, Frequency, and Period ===== |
| Here's a good introductory video for this section:((Dave Castler makes his videos for American Licences, which don't completely match the Canadian licences, but the concepts are the same.)) | |
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| {{ youtube>lrfLk2kjwMc }} | |
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| Here are two moving waves (press the play {{/play.png}} button on the bottom left corner of the picture). What's different about them? What's the same? | Here are two moving waves (press the play {{/play.png}} button on the bottom left corner of the picture). What's different about them? What's the same? |
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| {{ggb>/howto/hambasics/sections/travelingwave.ggb 800,250}} | {{ggb>/hambasics/sections/travelingwave.ggb 800,250}} |
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| To quantify these observations more precisely, let's look at a snapshot of both waves frozen in time. | To quantify these observations more precisely, let's look at a snapshot of both waves frozen in time. |
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| {{ howto:hambasics:sections:travelingwaves.png }} | {{ hambasics:sections:travelingwaves.png }} |
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| * the //amplitude// is the vertical height from the centre of the wave to its highest (or lowest) point. <fc #0014a8>The blue wave has an amplitude of 2</fc> and the <fc #008000>green wave has an amplitude of 1</fc>. | * the //amplitude// is the vertical height from the centre of the wave to its highest (or lowest) point. <fc #0014a8>The blue wave has an amplitude of 2</fc> and the <fc #008000>green wave has an amplitude of 1</fc>. |
| </WRAP> | </WRAP> |
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| Note that the reason we're using just 300, instead of 300,000,000 is that we've cancelled 6 of the zeros so that the frequency is in MHz instead of in Hz. | Note that the reason we're using just 300, instead of 300,000,000 is that we've cancelled six of the zeros so that the frequency is in MHz instead of in Hz. |
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| Now, here's a related question: how long does it take for each wave to complete one cycle? | Now, here's a related question: how long does it take for each wave to complete one cycle? |
| When two waves overlap, they add up together at every point. Here, the <fc #4682b4>blue</fc> and <fc #008000>green</fc> waves are generated and add up together to form the <fc #ff0000>red</fc> wave. You can move the blue and green waves and see the result. To convince yourself that the red wave is really the sum of the blue and green waves, look at points <fc #4682b4>A</fc>, <fc #008000>B</fc>, and <fc #ff0000>C</fc>. You can move the blue or green waves by sliding their phase (<fc #4682b4>φ</fc> and <fc #008000>Φ</fc>) around. You'll see that point <fc #ff0000>C</fc> is always the sum of <fc #4682b4>A</fc> and <fc #008000>B</fc>. | When two waves overlap, they add up together at every point. Here, the <fc #4682b4>blue</fc> and <fc #008000>green</fc> waves are generated and add up together to form the <fc #ff0000>red</fc> wave. You can move the blue and green waves and see the result. To convince yourself that the red wave is really the sum of the blue and green waves, look at points <fc #4682b4>A</fc>, <fc #008000>B</fc>, and <fc #ff0000>C</fc>. You can move the blue or green waves by sliding their phase (<fc #4682b4>φ</fc> and <fc #008000>Φ</fc>) around. You'll see that point <fc #ff0000>C</fc> is always the sum of <fc #4682b4>A</fc> and <fc #008000>B</fc>. |
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| {{ggb>/howto/hambasics/sections/waveaddition.ggb 800,500}} | {{ggb>/hambasics/sections/waveaddition.ggb 800,500}} |
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| Modulation is the process of "encoding" a message (be it voice or digital) onto a radio wave. | Modulation is the process of "encoding" a message (be it voice or digital) onto a radio wave. |
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| {{ youtube>D9Oa6jaHwtA }} | ===== Activity ===== |
| | If you have access to an HF radio: |
| | - Tune in to an AM signal and notice what happens as you slowly move off frequency: |
| | - How does the quality of the audio change? |
| | - How far can you go before you can't understand the audio anymore? |
| | - Tune in to an SSB signal and notice what happens as you slowly move off frequency: |
| | - How does the quality of the audio change? |
| | - How far can you go before you can't understand the audio anymore? |
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| {{ fm02.png }} | {{ fm02.png }} |
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| Here, the math is a bit more involved and requires at least 1<sup>st</sup> year calculus to understand but in a nutshell, if the carrier is \$$ c(t) = \cos(2 \pi f_c t) \$$ and the baseband signal is \$$s(t)\$$, then the FM signal will be: | Here, the math is a bit more involved and requires at least 1<sup>st</sup> year calculus to understand but in a nutshell, if the carrier is \$ c(t) = \cos(2 \pi f_c t) \$ and the baseband signal is \$s(t)\$, then the FM signal will be: |
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| <WRAP centeralign> | <WRAP centeralign> |
