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Why can shortwave radio waves travel for thousands of kilometers without loosing strong signal?

themctipers
By themctipers
in Hobby Electronics
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Go to solution Solved by DragonTamer1,

It's a bit tricky to put into words if you don't have a background in electronics. I'm going to try my best though so don't judge me too hard.

 

Above the earth there is a layer of the atmosphere called the ionosphere. It has a property that allows it to reflect radio waves, however it is better at reflecting longer wavelengths (AM) than shorter wavelengths (FM) The shorter wavelengths get distorted and dispersed while the longer wave lengths can get through with a signal that can still be picked up. This is why when you get further away from an AM radio station the quality is significantly worse than when you are closer (especially over the distance of several hundred miles) because the audio you are hearing is passing through the ionosphere first.

 

Higher frequencies have more of a tendency to pass through the ionosphere than reflect off of it, this is why satellite communications use even higher frequencies than FM (need to get the signal through).

 

Also, the ionosphere is not a fixed distance from the earth's surface. During the day it becomes more energetic from sunlight passing through it and it expands getting closer to the surface of earth. At night it settles and recedes. This is why you can usually hear AM stations from further away during the night.

Posted

Why can shortwave radio waves travel for thousands of kilometers without loosing strong signal? For example I can tune into a shortwave radio station in the southern east of the US but I can't tune into any US FM/AM stations using my radio.

 

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138 is a good number.

 

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FM = high quality, low range

 

AM = low quality, high range 

 

SW = lowest quality, highest range

 

or something like that...

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7 minutes ago, roblesaturcamilo said:

FM = high quality, low range

 

AM = low quality, high range 

 

SW = lowest quality, highest range

 

or something like that...

yeah but why and how can it have high range?

also the quality is pretty good, considering I can listen to WWCR in toronto with AM quality with minimal static and hissing on a cheap radio.

 

Ryzen 5 3600 stock | 2x16GB C13 3200MHz (AFR) | GTX 760 (Sold the VII)| ASUS Prime X570-P | 6TB WD Gold (128MB Cache, 2017)

Samsung 850 EVO 240 GB 

138 is a good number.

 

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It's a bit tricky to put into words if you don't have a background in electronics. I'm going to try my best though so don't judge me too hard.

 

Above the earth there is a layer of the atmosphere called the ionosphere. It has a property that allows it to reflect radio waves, however it is better at reflecting longer wavelengths (AM) than shorter wavelengths (FM) The shorter wavelengths get distorted and dispersed while the longer wave lengths can get through with a signal that can still be picked up. This is why when you get further away from an AM radio station the quality is significantly worse than when you are closer (especially over the distance of several hundred miles) because the audio you are hearing is passing through the ionosphere first.

 

Higher frequencies have more of a tendency to pass through the ionosphere than reflect off of it, this is why satellite communications use even higher frequencies than FM (need to get the signal through).

 

Also, the ionosphere is not a fixed distance from the earth's surface. During the day it becomes more energetic from sunlight passing through it and it expands getting closer to the surface of earth. At night it settles and recedes. This is why you can usually hear AM stations from further away during the night.

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They do lose power, but the dampening is proportional to the frequency. Despite to the name, SW radios have actually a very low frequency compared to modern systems like WLAN. Also they usually transmitts several kW of power.

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