What is the reason that high frequency radio wave experience more attenuation compare to low frequency radio wave? Is high frequency experiences attenuation at high distance or at low distance?
[Physics] the reason behind high frequency radio wave attenuates faster compare to low frequency
frequencyradio frequency
Related Solutions
In amplitude modulation, the frequency of the carrier wave is constant. The frequency spectrum of an AM signal includes sidebands, but those aren't the carrier wave. In your second figure, the carrier wave is the black line. You'll note that the amplitude changes; it increases and decreases in accordance with the modulation, however the frequency of this wave does not change. That is the essence of amplitude modulation. For a carrier wave of constant frequency, the information is encoded in the amplitude of the signal. The presence of sidebands does not imply the frequency is non-constant, merely that the overall signal is not a single pure frequency. The carrier still remains the same throughout and the frequency of the AM wave is connotatively the same as the frequency of the carrier.
EDIT: In the interest of avoiding spreading misleading information, I have removed the portions of this answer that have been disputed or refuted in the comments and edits on this question. Specifically, the parts about the ACK/Distance shown on the screen at 42:47 and the calculation of the curvature have been removed. The rest of this answer, however, still stands.
TL;DR: They erroneously believed that radio antennae were lasers. The antennae should still be able to connect even on a curved Earth.
The video pretends that the signal leaving the radio antennae is like a laser beam, focused in the line that emanates from transmitter to receiver without diverging. In reality, this isn't even close to true, even for directional radio antennae. Both the transmitted signal and the receiver acceptance get wider farther from the respective antennae, purely due to the diffractive properties of waves. This means that the signal actually propagates in a large ellipsoidal region between the antennae called the Fresnel zone**. The rule of thumb that is used in engineering systems is that as long as at least 60 percent of the Fresnel zone is unobstructed, signal reception should be possible.
The maximum radius $F$ of the Fresnel zone is given in the same Wikipedia article by
$$F=\frac{1}{2}\sqrt{\frac{cD}{f}}\,,$$
where $c=3\times {10}^8 \frac{\mathrm{m}}{\mathrm{s}}$ is the speed of light, $D$ is the propagation distance and $f$ is the frequency. Using $D=14 \, \mathrm{km}$ and $f=5.880 \, \mathrm{GHz},$ we see that $F=13.69 \, \mathrm{m}.$ As you can see, the beam expands massively over such a distance. If you cut out the lower $3.84 \, \mathrm{m}$ of that circle, you would find that the fraction of the beam that is obstructed for obstruction height $h$ from the formula for the area of the cut-out portion given here:
$$\frac{A_{\text{obstructed}}}{A_{\text{whole beam}}}=\frac{F^2\cos^{-1}\left(\frac{F-h}{F}\right)-(F-h)\sqrt{2Fh-h^2}}{\pi F^2}\,.$$
Evaluating this expression for $F=13.69 \, \mathrm{m}$ and $h=3.84 \, \mathrm{m}$ gives you an obstruction fraction of $\frac{A_{\text{obstructed}}}{A_{\text{whole beam}}}=0.085.$
So, even on a curved earth, only 8.5 percent of the beam would be obstructed. This is well within the rule of thumb (which required less than 40 percent obstruction), so the antennae should still be able to connect on a curved Earth.
**In reality, propagation of radio waves between two antennae is complicated, and I'm necessarily skipping over a lot of details here, or else this post would become a textbook. What I refer to as the "Fresnel zone" here is technically the first Fresnel zone, but the distinction is not necessary here.
Best Answer
There is no attenuation in free space, no matter what the frequency. Other mediums (like the atmosphere) have their unique attenuation spectra. For radio frequencies, there is more attenuation through the atmosphere for higher frequencies because they are better absorbed by the moisture in the air.