Why high frequency waves cannot be used in sky waves?

In summary, sky waves transmission uses total internal reflection to reflect waves as they pass from a denser medium to a rarer one. However, high frequency waves cannot be used for this type of transmission because their refractive index is greater, making total internal reflection easier and resulting in the waves penetrating the atmosphere. This is similar to how ultraviolet light is absorbed in glass due to its high frequency. The ionosphere also plays a role, as when frequencies near its plasma frequency are used, the electrons are not able to effectively reflect the waves and they are instead absorbed. More information can be found on Wikipedia's page on the ionosphere.
  • #1
jd12345
256
2
Sky waves transmission is done using the total internal reflection phenomena. The waves reflect as we go to a rarer medium from a denser medium.
My book states that high frequency waves cannot be used for sky waves. IT says it will penetrate the atmosphere. I don't get it

refractive index for high frequency waves is greater so they will be refracted and hence their total internal reflection will be easier

Any help? Thank you
 
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  • #2
I think the answer lies in that the phenomenon cannot be understood as simple internal reflection of visible light on the boundary glass-air. There indeed the violet light should reflect even better than red light.

The difference with ionosphere is that if the frequency gets high enough (near its plasma frequency), the electrons are not able to function as effective refelctors and the wave penetrates the layer and is damped down there instead. The same thing happens in optics, when we use ultraviolet light - this gets absorbed in glass as well.

There is also short explanation on Wikipedia (middle of the page)
https://en.wikipedia.org/wiki/Ionosphere
 

Related to Why high frequency waves cannot be used in sky waves?

1. Why can't high frequency waves be used in sky waves?

High frequency waves have shorter wavelengths, which means they are easily absorbed by the Earth's atmosphere. This makes it difficult for them to travel long distances through the atmosphere and reflect off the ionosphere, which is necessary for sky wave propagation.

2. What happens to high frequency waves when they encounter the ionosphere?

When high frequency waves reach the ionosphere, they can be refracted, absorbed, or scattered. This can cause the waves to lose energy, making it difficult for them to travel long distances through the ionosphere and be received on the other side.

3. Can high frequency waves be used for sky wave communication in certain circumstances?

Yes, high frequency waves can be used for sky wave communication in certain circumstances, such as during periods of high solar activity. During these times, the ionosphere becomes more ionized and can reflect higher frequency waves, allowing for longer distance communication.

4. Are there any other factors besides the ionosphere that affect the use of high frequency waves in sky wave communication?

Yes, there are other factors that can affect the use of high frequency waves in sky wave communication. These include weather conditions, time of day, and the angle at which the waves enter the ionosphere.

5. How does the use of high frequency waves in sky wave communication compare to other types of waves?

Compared to other types of waves, such as low frequency or medium frequency waves, high frequency waves are more easily absorbed by the Earth's atmosphere. This makes them less reliable for long distance communication, but they can still be used in certain circumstances as mentioned earlier.

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