"Antoņio" wrote in message
...
I am not sure. Is it because the radiation pattern is spherical and not
line-of-sight?
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.
As an example, let's say you're flying from EAU VOR to LAN VOR at 15,500'.
They're about 320 miles apart but at that altitude line-of-sight distance is
about 180 miles so you should receive LAN before losing EAU, even though
you're well outside of the standard service volume of forty miles. When
you're about halfway you switch from EAU to LAN, but you're unable to get a
reliable signal.
The problem may be that you're closer to ESC and RFD VORs than you are to
LAN, and they all operate on 110.8.
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