howto:hambasics:temp
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- | ====== Amplitude, Wavelength, Period, and Frequency ====== | ||
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- | '' | ||
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- | Imagine that the dots moving up and down are creating the waves that are travelling to the right (as we'll see later, this is kind of like how radio waves are created). | ||
- | - The Blue wave is twice as " | ||
- | - Both waves are travelling to the right at the same speed. | ||
- | - The Blue dot is moving up and down three times as fast as the green dot. | ||
- | - The Blue wave is three times as compressed as the green wave. | ||
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- | To quantify observations more precisely, let's look at a snapshot of both waves. | ||
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- | '' | ||
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- | - the // | ||
- | - the // | ||
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- | All EM waves (radio, light, etc) in vacuum travel at the speed, which is roughly 300,000 metres per second. | ||
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- | Look at the following two waves. | ||
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- | {{wave1.png? | ||
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- | At first sight: | ||
- | - the first one is " | ||
- | - the first one is also " | ||
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- | These two observations can be quantified very precisely as: | ||
- | - the // | ||
- | - the //period//: **horizontal** length of one complete cycle. | ||
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- | {{ wave3.png | ||
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- | So the previous two waves have: | ||
- | - Amplitude = 2, Period = 0.05 ms | ||
- | - Amplitude = 1, Period = 0.02 ms | ||
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- | {{wave1.png? | ||
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- | The amplitude is normally related to the strength of the signal (like the volume for sound). | ||
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- | Since the period (//T//) is the amount of time it takes to complete one cycle, and the frequency (//f//) is the number of cycles in one second, the period and the frequency are inverses of each other: | ||
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- | < | ||
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- | <box 80% blue> | ||
- | In this course, we'll see a few formulas and it'll be tempting to memorize them but let's instead understand what they really mean... | ||
- | </ | ||
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- | For example: | ||
- | * if the period is half a second, we can fit 2 full cycles in one second. | ||
- | * If the period is a quarter of a second, the frequency is 4. | ||
- | * If the period is a tenth of a second, the frequency is 10. | ||
- | * If the period is T seconds, the frequency is $\frac{1}{T}$ ( $\frac{1}{0.5} = 2, \quad \frac{1}{0.25} = 4, \quad \frac{1}{0.1} = 10$ ) | ||
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- | Right? | ||
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- | So for the previous two waves, the frequencies would be: | ||
- | * < | ||
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- | * < | ||
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- | Recall that //Hz// means "cycle per seconds" | ||
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- | Let's now look at three different ways to encode a signal on a radio wave. | ||
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- | FIXME: add $f=\frac{c}{\lambda}$ | ||
howto/hambasics/temp.1574727534.txt.gz · Last modified: 2019/11/25 16:18 by ve7hzf