Refraction vs Frequency Question

[snoobeagle]

Hi All,

I'm studying for a Ham Radio test and can't for the life of me understand the mechanism behind higher (in this case, Radio) frequencies leading to less refraction in (again in this case, the ionosphere) mediums. I'm sure light waves/dense transparent media has the same explanation.

I've seen some good threads here on frequency being constant and wavelength/velocity changing. Does anyone have the extra step on why the bending is more for lower frequencies?

Thank you!

 

[peterjaybee]

The Ionosphere is a special type of medium and requires plasma physics to describe it as you have electromagnetic waves (in this case the radiowaves) interacting with charged particles which generate complex electric and magnetic fields.

I don't know your knowledge of plasma physics, and mine is limited, but the electrons in the plasma occilate at a frequency called the electron plasma frequency. This osscillation occurs due to the interaction of electrons with each other.

The propogation of electromagnetic waves through the plasma is determined by their frequency relative to this electron plasma frequency. For example, a wave with frequency less than the electron plasma frequency will be reflected at the interface.

Hope I havnt gone off topic

 

[snoobeagle]

Thanks Peter! Knowing there is a complex mechanism behind it such as the plasma oscillation frequency helps to make it more intuitive. I hope to get to a point where I can make a frequency choice as second nature by knowing current conditions of the ionosphere.

Neil