Satgen 157 Distorted/Misleading Satellite and Ionosphere Plots 29Mar 92 A recent spate of letters and packet queries have concerned Radio Amateurs confused by Handbook and Magazine illustrations showing grossly distorted views of the Ionosphere and/or Satellite communications cover. Even with computer software the instructions often create totally false expectations. Eg many programs purporting to work for all satellites, carry a section which tells you when the satellite is jointly in range of UK and San Francisco, indicating when communication is possible. But if you try to use this program for Mir or the Space Shuttle you get a complete blank. Because Mir's low altitude restricts it to a very limited view of the earth surface at any one time. You can avoid being mislead if you remember the rough rules whereby satellites height determines how far away you can follow it ( the so called FOOTPRINT RADIUS ), and twice the FOOTPRINT RADIUS gets you the maximum possible separation for two stations communicating through the satellite. Useful examples are :- Satellite Height above Earth Footprint radius Max Communication range SHUTTLE 296 km average 1890 kms No 2 way transpond MIR 400 2224 4448 kms RS 12 1000 3336 6672 kms Fuji 20 1500 at apogee 4000 8000 kms Arsene 36000 (launch July?) 9050 18100 kms Oscar 13 38000 approx 9100 18200 kms So please check which satellite you are using , remembering that its height will govern its communications link range. A similar problem of distortion afflicts the illustrations of ionospheric signal paths shown in many magazines and handbooks. RSGB Radio Communication Magazine recently published illustrations of an Ionosphere which was drawn 3200 kms above the earth , thereby appearing to provide a fat distorted communications channel for signal propagation via ionospheric refraction and forward scatter. In fact this distortion of the ionosphere by nearly ten times its normal height, gave a lot of novices and old timers the impression ,that the conditions described would support large angles of vertical incidence in the signal propagation path and fierce angles of ground reflection. In fact the simple very thin channel presented by the really ionosphere makes these crazy geometries quite impractical and grossly misleading. So please remember that neither the Ionosphere. or the vast majority of satellites in low earth orbit ,are all that far above the earth . Do not get caught by either these RadCom absurdities, or, magazine or software instructions that do not tell the true story. 73 de GM4IHJ @ GB7SAN