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I finally went and got my Ham Radio licence. I've been reading about how radio operators use the ionosphere for long distance communication through ionic reflections of transmitted/received EM waves.

I'm trying to visualize how this happens, so that I have more intuition into what frequencies to use under various conditions of the ionosphere.

Can someone give an illustration of how EM waves are reflected by ions in the ionosphere, to help convey pictorially why wavelength matters?

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The way I look at it is as follows:

Flat surfaces reflect waves well. Jagged, rough surfaces scatter them. The ionosphere is not a well defined area but a diffuse region - roughly the same altitude over a very large area, but jagged at any specific point.

Now, imagine a rugged surface like an well played-upon sports field with lots of cleat-marks. Then zoom out. The further away you are, the flatter the surface will appear. The closer it is, the more irregular it will appear. The longer the wavelength (lower the frequency) the more smooth it appears, and thus the better reflector it will become.

Thus lower frequencies generally provide better skywave (reflected from the ionosphere) performance. But since everyone wants to use those lower frequencies and because of pink (skewed towards the lower end of the spectrum) noise from electronics and other man-made devices, there is a tradeoff to be made.

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  • \$\begingroup\$ No, it is not the irregularity. Rather it is a question if the charge density causes sufficient dispersion at a given frequency to achieve reflection. In cases of actual irregularity - for example intense ionization trails left by meteors - VHF & UHF frequencies become usable. \$\endgroup\$ Nov 10, 2015 at 20:25

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