I was at a CFI safety meeting today and the subject of VOR service
volumes came up. The AIM describes the Standard High Service Volume as
providing positive course guidance at varying distances depending on
your altitude--40nm at 1000ft., 100nm at 14,500ft, 130nm at 45,000ft, etc.

If the VOR is a "line of sight" signal device. How can there be varying
distances of service at varying altitudes? I mean, shouldn't I be able
to pick up a VOR radial from the moon as long as no obstructions intervene?


Antonio