Effects on ionosphere

by: Tymon Hytem
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Word Count: 459

A solar eclipse causes a decrease in the critical frequency of E and F1 layer. The variation of critical frequency is approximately in phase with the optical eclipse. The ionization in E and F1 layer results from solar radiation having speed closely agreeing with that of light. The influence of the solar eclipse on the F2 region is relatively less. Meteors may produce enough ionization in the upper atmosphere so as to appreciably effect radio wave propagation. The meteors may account for sporadic E layer effects. Sporadic E layer effects are when radio waves are returned are returned to earth by the E layer at frequencies considerably greater than the critical frequency of the layer. These are believed to be caused by partial reflections from sharp boundaries to stratified ionization. Further the ionizing effects of the minute meteors continuously received by the earth may at least partially account for the ionization that remains in the ionosphere at night time. Irregularities in electron distribution in the ionosphere causes scattered reflections of radio waves. These reflected signals are generally weak, irregular and diffused and may be caused in any of the layers. Further these reflected signals some times become quite complex because of the interaction between layers. The vertical heights of scattered reflections depend upon the type of scattering and may lie between ninety to about fifteen hundred kilometers. Scatter reflections are also caused when an ionosphere wave on refraction from the ionosphere strikes the earth. The scattered energy then propagates away from the point of scatter refraction in the same general way as that from a transmitting antenna. How ever the signals so produced are some forty decibels weaker than the main signals. Scattering of radio waves may be radiated usefully utilized in the following waves that is scatter signal may be radiated within the skip region and with highly directional transmitting antenna, a receiving antenna lying appreciably to one side of the path of the main beam may also adequately receive the signal as caused by scattered wave traveling at right angles to the main beam.

The effect produced by the ionosphere on a radio wave is not linear that is not proportional to the magnitude of the wave, hence two strong radio waves passing through the ionosphere concurrently may interact to produce cross modulation products. The magnitude of such a cross modulation may in some cases be large enough to produce appreciable effect. First such interference reported involved radio Luxemburg. Hence the effect is termed as Luxemburg effect. But the Luxemburg effect has not been generally observed with even most powerful transmitters. Hence there is a possibility that the effect might have been produced by external cross modulation instead of cross modulation in the ionosphere.

About the Author

Tymon Hytem has worked in the electronics field for the past 15 years. He enjoys helping people decide on electronic gadgets from telephones to XM Radio and choosing the perfect XM Satellite Radio system for their needs.

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