### Table giving optimum antenna beam elevations and offset angles for forward-scatter MS links of various distances,

taken from AMS Bulletin No. 203, "The AMS Radiometeor Project."
__RANGE (km)__ | __RANGE (mi)__ | __ELEVATIONS__ | __AZIMUTH OFFSETS__ |

500 | 310 | 18 | 21 |

600 | 373 | 15 | 18 |

700 | 434 | 13 | 16 |

800 | 497 | 11 | 15 |

900 | 559 | 9 | 14 |

1000 | 621 | 8 | 13 |

1200 | 746 | 6 | 11 |

1500 | 932 | 4 | 10 |

1800 | 1118 | 2 | 10 |

2000 | 1243 | 1 | 10 |

2500 | 1553 | 0 | 8 |

The offset angles come from the fact that most meteor reflections will not come from meteors directly between the transmitter and receiver, but instead tend to most frequently come from two "hot spot" regions about 50-150 km to either side of the transmitter-receiver great circle path midpoint. The offset angles are approximate angles which the antenna should be pointed to either left or right away from the direct bearing of the other station. For small antennas and distances over about 1200 km, these are not important. For large arrays at shorter distances, and for all but the smallest antennas at distances less than about 800 km, these can become very important. For sporadic meteors, an azimuth on either side of the direct path can be used; but both stations must offset in the same direction!

For more information, see "moreon50.txt" in the OH5IY MSSoft package; "VHF Propagation by Meteor-Trail Ionization" by W4LTU (reprinted in *Beyond Line of Sight*, ARRL, p. 115); *The VHF/UHF DX Book* p. 2-58 from RSGB; and the various professional literature.

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A general idea of the distance to an individual meteor as a function of meteor altitude can be gained using a law of cosines function, drawing a triangle using the observer, the meteor, and the center of the Earth. This will give the relationship:

(r + h)^2 = r ^2 + d^2 - (2 * r * d * cos (90 + theta))

where

r=Earth radius (km) (6370 km)

h=height of meteor above the surface (km) (80-120 km)

d=distance between observer and meteor (km)

theta=angular height of meteor above the horizon (degrees)