Steven P. McNicoll wrote:

You're looking at just one VOR at a time. There are about 1000 VORs in the
US and just 100 VOR frequencies. The service volume has to ensure not only
usable reception of the desired VOR, but non-reception of undesired VORs on
the same frequency.

Ok...I think I'm with you (though feeling like I might be exhibiting
that I am a little obtuse at this point in the discussion). I assume
that your post means you think I haven't quite got it yet?

Are you saying that the service volume diagrams are artist renderings of
the reception distances that the FAA have tested and will *guarantee* to
be usable?? So the "double/inverted wedding cake" structure (which, as
you recall, was the basis of my original question) really has little to
do with the *actual* signal propagation distances of a particular VOR
but, rather, provide approximations by taking into consideration the
real world interference of other VORs, spherical wave radiations,
curvature of earth, etc. ?

So I would not necessarily loose VOR service if, while using a Standard
High Altitude Service Volume station, I were to climb above FL45, with a
depicted service distance of 130nm, to FL46 with it's depicted service
distance of 100nm?

Antonio (thinking he had it, then....)