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Tonight,hopefully, some of us should be able to see a nice meteor display.

Meteor burst communications utilize amost unusual propagation mode, as you can read about in the attached article.

http://news.yahoo.com/s/ap/20091208/ap_on_sc/us_sci_meteor_shower

http://en.wikipedia.org/wiki/Meteor_burst_communications


http://www.meteorcomm.com/technologies/tech_burst_tech.aspx

Note the references to the use of phase arrayed antenna systems, which should be familiar to you from your 802.11n studies [ beam-forming in MIMO ].


Radio waves will bend or ???¡é?¡é?????¡­?¡°refract???¡é?¡é???????? in the presence of charged particles. It is a different form of refraction from that which occurs when an 802.11 radio wave refracts when passing from one media to another, but bending does take place. High frequency [ HF ] radio communications [ short wave ] occurs when radio waves of a certain frequency [ 3-30 Mhz approximately ] pass through a layer of ionized particles above the earth???¡é?¡é?????¡é???¡és surface known as the ionosphere.

http://www.spectratek.co.nz/images/propagation_night_time.gif


Radio waves of a certain frequency can also be ???¡é?¡é?????¡­?¡°ducted???¡é?¡é???????? from one place to another by being channeled through a layer of air of one temperature trapped between two other layers. This is called tropospheric ducting and occurs mostly in tropospheric scatter radio systems.
http://www.northatlanticradiosystem.com/abttropo.htm


I used to see this in a middle eastern country I used to work in. During certain times of the year, UHF [ 300-3000 Mhz ] TV signals from another country hundreds of miles away would come blasting through onto our TV screens.

Another phenemenon called ionsospheric scintillation can affect GPS signals and needs to be taken into account by the GPS control station software.

http://ess.nrcan.gc.ca/rrnh-rran/proj3_e.php


Dave