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howto:hambasics:wavemodulation [2020/10/07 07:58] – ↷ Links adapted because of a move operation va7fihowto:hambasics:sections:wavemodulation [2022/11/04 18:52] (current) – [AM] va7fi
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-|<100% ----- >| 
-|  [[home |Ham Basics]]  |  [[test |About The Test]]  |  [[Reference |References]]  ^  [[sections |Study Sections]]  | 
- 
 ====== Properties of Waves ====== ====== Properties of Waves ======
 +
 Here we dive a little more deeply into waves and look at three ways that a "pure" radio wave (called the //carrier//) can be modulated to encode a voice signal (called the //baseband// signal):  //AM, SSB, FM//. Here we dive a little more deeply into waves and look at three ways that a "pure" radio wave (called the //carrier//) can be modulated to encode a voice signal (called the //baseband// signal):  //AM, SSB, FM//.
  
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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.)) 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.))
  
 {{ youtube>lrfLk2kjwMc }} {{ youtube>lrfLk2kjwMc }}
  
-Here are two moving waves.  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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-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).  Here are a few things to notice:+Imagine that the dots moving up and down create the waves that are travelling to the right (as we'll see later, this is kind of like how radio waves are created).  Here are a few things to notice:
   - The Blue wave is twice as "tall" as the green wave.   - The Blue wave is twice as "tall" as the green wave.
   - Both waves are travelling to the right at the same speed.   - Both waves are travelling to the right at the same speed.
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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.
  
-{{ :howto:hambasics:travelingwaves.png }}+{{ howto:hambasics:sections:travelingwaves.png }}
  
   * 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>.
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 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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   * the red wave is cancelled out?((Fun fact: This is how [[wp>Active_noise_control |noise cancelling headphones]] work.  The headset has a microphone that picks up the noise, inverts the waves, and plays them back in the ear piece.  The combination of the real life noise and the inverted noise being played in the speaker cancel out (somewhat).))   * the red wave is cancelled out?((Fun fact: This is how [[wp>Active_noise_control |noise cancelling headphones]] work.  The headset has a microphone that picks up the noise, inverts the waves, and plays them back in the ear piece.  The combination of the real life noise and the inverted noise being played in the speaker cancel out (somewhat).))
  
-If you press the play button on the bottom left corner, you'll see the blue wave travel to the right and the green wave travel to the left.  The red wave oscillates up and down but doesn't travel anywhere.  This is called a //standing wave//, which we'll see again later when we discuss SWR.+If you press the play button {{/play.png}} on the bottom left corner, you'll see the blue wave travel to the right and the green wave travel to the left.  The red wave, which is the sum of the forward and reflected waves, oscillates up and down but doesn't travel anywhere, which means it's not going into the antenna.
  
 +While the animation is running, slowly decrease the amplitude of the reflected wave (<fc #008000>V<sub>B</sub></fc>) and you'll see that the red wave will start moving to the right.  As you do that, notice how the SWR (Standing Wave Ratio) decreases toward 1:1.  At this point, there is no reflected wave and all of the energy is going to the antenna (assuming no loss in the feedline).  
  
 ====== Modulation ====== ====== Modulation ======
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 <WRAP center round important box 80%> <WRAP center round important box 80%>
-Let's pause for a minute and highlight that here, we are **multiplying** two waves together (not simply adding them).  Later on, we'll see that the electronic component that does that is called a //mixer//, not to be confused with an sound mixer, which does do addition.  +Let's pause for a minute and highlight that here, we are **multiplying** two waves together (not simply adding them).  Later on, we'll see that the electronic component that does that is called a //mixer//, not to be confused with sound mixer, which does do addition.  
 </WRAP> </WRAP>
  
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-Note that the carrier as a frequency of 200 kHz just like the original carrier, but the two side bands are 10 kHz lower and higher with half of the amplitude.  Notice also how the <fc #800000>LSB Wave</fc> oscillates slower than the <fc #4682b4>Carrier Wave</fc>, while the <fc #008000>USB Wave</fc> oscillates faster.+Note that the carrier has a frequency of 200 kHz just like the original carrier, but the two side bands are 10 kHz lower and higher with half of the amplitude.  Notice also how the <fc #800000>LSB Wave</fc> oscillates slower than the <fc #4682b4>Carrier Wave</fc>, while the <fc #008000>USB Wave</fc> oscillates faster.
  
  
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   * The two side bands are 10 kHz on each side of the carrier (same as the <fc #ff0000>baseband</fc> signal!).  It is that distance away from the carrier that represents the audio signal we want to recover.   * The two side bands are 10 kHz on each side of the carrier (same as the <fc #ff0000>baseband</fc> signal!).  It is that distance away from the carrier that represents the audio signal we want to recover.
   * Most of the power is going into transmitting the carrier, which in itself doesn't carry any information, so that's a bit of a waste of energy.   * Most of the power is going into transmitting the carrier, which in itself doesn't carry any information, so that's a bit of a waste of energy.
-  * More fundamentally: even though we say that the signal is transmitted at 200 kHz, in this example, it is really contained between 190 kHz and 210 kHz.  That is, it has a bandwidth of 20 kHz (210 kHz - 190 kHz).  This bandwidth is regulated and depends on the [[.sections:intro#full_frequency_list| band used]].+  * More fundamentally: even though we say that the signal is transmitted at 200 kHz, in this example, it is really contained between 190 kHz and 210 kHz.  That is, it has a bandwidth of 20 kHz (210 kHz - 190 kHz).  This bandwidth is regulated and depends on the [[intro#full_frequency_list| band used]].
  
 ===== SSB ===== ===== SSB =====
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 For those interested in some of the mathematical details, see this [[wavemodulationmath |optional page]]. For those interested in some of the mathematical details, see this [[wavemodulationmath |optional page]].
  
-[[.sections:intro|{{/back.png }}]] [[mathbasics |{{  /next.png}}]]+[[intro|{{/back.png }}]] [[mathbasics |{{  /next.png}}]]
  
howto/hambasics/sections/wavemodulation.1602082712.txt.gz · Last modified: 2020/10/07 07:58 by va7fi