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Author Topic: T3C11  (Read 706 times)

TRUTHSEER

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T3C11
« on: June 25, 2019, 09:46:12 AM »

Given the characteristic of electro magnetic waves being hindered the travel by larger vs minimal earth curvature, man made and natural structures, wouldnt it be more accurate to say the ability for VHF and UHF bands to travel further than line of sight is more of a ionosphere reflection combined with the power of those frequencies?  Just asking.
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N8AUC

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RE: T3C11
« Reply #1 on: June 25, 2019, 12:03:34 PM »

Keep reading and studying.

Ionospheric propagation is normally limited to the HF bands, below 30 MHz. Occasional exceptions to that occur on 6 meters, and even more rarely on 2 meters, both of which are VHF bands. It almost never happens at UHF and above.

The reason for that is that the energy contained in a radio wave increases with frequency. Planck's equation describes this.
When the energy in the wave is higher than the ionosphere can refract for a given level of ionization, it passes through the ionosphere rather than being refracted back to earth.

Generally speaking VHF, UHF, and higher frequency radio waves possess too much energy for the ionosphere to refract.

The curvature of the earth does little to hinder the propagation of electromagnetic waves, unless the altitude of a particular geographic feature literally "gets in the way of line of sight".
Radio waves usually will not propagate through dirt, and they are often blocked my man-made structures. Especially those made of metal, or reinforced by metal (think rebar in concrete).
Structures made of non-conductive materials, such as a wood-sided house, have little effect.

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K4EMF

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RE: T3C11
« Reply #2 on: June 25, 2019, 12:39:01 PM »

This might not directly answer the question but it does give some good explanations of propagation

http://w6yra.bol.ucla.edu/class2/T10_weak_signal.pdf
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TRUTHSEER

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RE: T3C11
« Reply #3 on: June 25, 2019, 01:39:42 PM »

Keep reading and studying.

I will, thanks.

Here's what Im getting at:

The curvature of the earth does little to hinder the propagation of electromagnetic waves, unless the altitude of a particular geographic feature literally "gets in the way of line of sight".
Radio waves usually will not propagate through dirt, and they are often blocked my man-made structures. Especially those made of metal, or reinforced by metal (think rebar in concrete).
Structures made of non-conductive materials, such as a wood-sided house, have little effect.

What makes the "bending" of radio waves to make the exam answer correct.
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W9IQ

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RE: T3C11
« Reply #4 on: June 25, 2019, 02:40:29 PM »

What makes the "bending" of radio waves to make the exam answer correct.

The effect in question is observed as the radio horizon which is slightly longer than the line of sight horizon.

Keep in mind that RF doesn't propagate in straight lines but rather in a curved or spherical front. The atmospheric layers create a refractive effect so that propagation paths are essentially curved - the degree of which is dependent upon the frequency. Because the refractive atmosphere is slightly above the surface of the earth that limits line of site distance, this elevated curving refractive effect adds about 15% to the effective path length.

This mechanism should not be confused with HF "skip" that occurs in the much higher E and F layers of the atmosphere.

- Glenn W9IQ

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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

TRUTHSEER

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RE: T3C11
« Reply #5 on: June 25, 2019, 06:59:49 PM »

Keep in mind that RF doesn't propagate in straight lines but rather in a curved or spherical front. The atmospheric layers create a refractive effect so that propagation paths are essentially curved - the degree of which is dependent upon the frequency. Because the refractive atmosphere is slightly above the surface of the earth that limits line of site distance, this elevated curving refractive effect adds about 15% to the effective path length.

This what I expect from knowledgeable individual radioists who can articulate complex subject matter.  Even though I may have an electronic background, the above rendition is what I am talking about concerning the understanding what is behind the mechanics of radio.

Glenn sir, I look forward to reading your input in future posits of pointed questions.
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