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en:lesson10 [2020/03/25 16:03]
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en:lesson10 [2021/04/06 09:43] (current)
golikov
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 ===== Theory ===== ===== Theory =====
  
-Doppler effect ​a change in the frequency of the signal, the observed ​movement of the signal source relative to the receiver. The effect is named after the Austrian physicist Christian Doppler.+The Doppler effect ​represents ​a change in the signal ​frequency occurring due to movement of the signal source relative to the receiver. The effect is named after the Austrian physicist Christian Doppler
 + 
 +The Doppler effect is easy to be observed in practice, when a car passes by with an alarm turned on. Let’s suppose an alarm produces a certain tone and it does not change. When the car is not moving relative to the observer, then the observer hears exactly the tone the alarm emits. But if a car approaches the observer, then the frequency of sound waves will be increased and the observer will hear a higher tone than the alarm actually emits. At the moment in which a car passes the observer, he\she will hear the same tone that the alarm actually emits. When the car passes farther away and is already moving away instead of coming closer, then the observer will hear a lower tone due to the lower frequency of sound waves.
  
-The Doppler effect is easily perceived in practice when a car with the siren turned on passes by the observer. Suppose a siren gives out a certain tone, and it does not change. Due to the fact that the car does not move relative to the observer. If the frequency of sound waves increases, and the observer hears a higher tone than actually because of the siren. At the moment when the car will pass by the observer. When the car goes further and is already approaching. 
  
 {{:​200px-doppler_effect_diagrammatic.png?​400|}} {{:​200px-doppler_effect_diagrammatic.png?​400|}}
  
 == Mathematical description of the phenomenon == == Mathematical description of the phenomenon ==
-If the wave source moves relative to the medium, then the distance between ​the wave crests ​(wavelength λ) depends on the speed and direction of movement. If the source moves towards the receiver, that is, it catches up with the wave emitted ​by it, then the wavelength decreasesif it moves awaythe wavelength increases:+ 
 +If source ​of waves moves relative to the medium, then the distance between wave extremes ​(wavelength λ) depends on the speed and direction of movement. If the source moves towards the receiver, that is, it catches up with the wave emitted, then the wavelength decreasesif it moves away - then the wavelength increases:
  
 {{:​1001.png?​150|}} {{:​1001.png?​150|}}
  
-where ω0 is the angular frequency with which the source emits waves, c is the speed of wave propagation in the medium, v is the velocity ​of the wave source relative to the medium (positive if the source ​approaches ​the receiver and negative if it moves away).+ω0 is the angular frequency with which the source emits waves, c is the speed of wave propagation in the medium, v is the speed of the wave source relative to the medium (it is positive if the source ​is approaching ​the receiver and negative if it is moving ​away).
  
-Frequency ​recorded by a fixed receiver+The frequency ​recorded by a stationary ​receiver
  
 {{:​1002.png?​200|}} {{:​1002.png?​200|}}
  
-Similarly, if the receiver moves towards the waves, it registers their crests ​more often and vice versa. ​For a fixed source and moving receiver+Similarly, if the receiver moves towards the waves, ​then it registers their extremes ​more often and vice versa. ​Stationary ​source and moving ​(mobile) ​receiver
  
 {{:​1003.png?​150|}} {{:​1003.png?​150|}}
  
-where u is the receiver velocity ​relative ​to the medium (positive if it moves towards the source).+where u is the receiver'​s ​velocity ​with respect ​to the medium (positive if the receiver ​moves towards the source). 
 + 
 +By substituting ω0 in the formula (2) for the frequency ω taken from formula (1), we obtain the formula applied for the general case:
  
-Substituting the frequency ω from formula (1) instead of ω0 in formula (2), we obtain the formula for the general case: 
  
 {{:​1004.png?​150|}} {{:​1004.png?​150|}}
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 ===== Observation of the Doppler effect ===== ===== Observation of the Doppler effect =====
  
-We will observe ​the Doppler effect using the example of receiving a telegraph code from satellites. ​Get ready for work and configure ​the necessary software as described in Lesson 09.+Observation of the Doppler effect ​will be provided ​using the example of telegraph code reception ​from satellites. ​Prepare equipment ​for operation ​and set up the necessary software as described in Lesson 09.
  
-Wait for a “good” ​satellite ​flight ​at least 30 ° above the horizon.+Wait for a "​proper and suitable" ​satellite ​to pass at least 30° above the horizon.
  
 {{:​image001_xw2a.png?​400|}} {{:​image001_xw2a.png?​400|}}
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 {{:​image004_xw2a.png?​200|}} {{:​image004_xw2a.png?​200|}}
  
-Output the sound to the headphonesand hear a change in the tone of the signal from a moving satellite.+Activate ​headphones and listen to the changing ​tone of the moving satellite.
  
 {{:​image003_xw2a.png?​400|}} {{:​image003_xw2a.png?​400|}}
  
-Turn on all the items in the Zoom FFT section.+Turn on all elements ​in the "Zoom FFT" ​section.
  
 {{:​image002xw2a.png?​200|}} {{:​image002xw2a.png?​200|}}
  
-The Auto Spectrum graph clearly shows how the frequency of passing satellite ​changes.+A user can check perfectly ​how the frequency of the passing satellite ​is changed in the "Auto spectrum"​ chart.
  
 {{:​image005_xw2a.png?​400|}} {{:​image005_xw2a.png?​400|}}
en/lesson10.1585141419.txt.gz · Last modified: 2020/03/25 16:03 by 127.0.0.1