Service Volumes of VOR's make no sense

Steven P. McNicoll wrote:

Yes, and every other VOR on that frequency as well. The altitude/distance
limits ensure you won't receive an unwanted VOR signal. Note that the
service volume decreases from 130 miles to 100 miles above FL 450.



Exactly! And that was the reason for my confusion and original question.

Antonio

Grumman-581 wrote:
"Antoñio" wrote in message ...

I'm not sure of what that remark means.


The earth is round... Radio travels line of sight, which means a straight
line...Draw a large circle with a protractor... Choose a point on the
circumference at the top of the circle... Draw a line tangent to the circle
through this point... The line is horizontal... If an object is above this
line, it will be able to 'see' the original point, if it is below the line,
but above the circumference, it will not be able to 'see' the original point
since the body of the circle (i.e. the earth) is getting in the way of the
signal... The greater the distance the object is above the circumference of
the circle, the more of the circle it is able to 'see'...

Now, extend this concept into three dimensions...


That argument would be acceptable if the service volumes were increased
at regular rates as one increased in altitude. However, according to the
AIM, they do not. In fact the configuration presented is non-linear.

Once again I say take a look at the drawings in the AIM of the service
volumes. The distances that VOR's of varying service offerings are
depicted to offer is schematically represented as sort of like stacked
tires of differing sizes! Your linear geometric model explanation just
does not hold up to what is pictured there in the AIM.

Antonio

Hilton wrote:


Yes, if we all had extremely efficient receivers, but we don't. The FAA and
some radio guys got together and decided on applicable distances. Once they
figured that out, they had a bunch of semi-spheres. While it would have
been 'correct' to define the service volumes are a semi-sphere, it wouldn't
have been all that useful to us (pilots). So the FAA made them (mostly)
cylinders (and ensured that the cylinder lay within the semi-sphere) to make
it easy for pilots to figure out whether or not they were in the service
volume. i.e. it is a combination of radio effectiveness and pilot
usefulness that describes the service volume.

I just made that up, but it sure sounds convincing, logical, and almost as
good as if I had stayed at a Holiday Inn last night... instead of working
on software.

Hilton

If the FAA simply depicted a cylinder of theoretical signal strength
within the actual "semi-sphere" of service, I would completely follow
the analogy.

However, the FAA has depicted cylinders of various diameters stacked
upon each other. Given that the VOR is line-of-sight, I did not
understand why, for example, a VOR would be received 130nm out at FL180
yet only be received 100nm at FL500. Doesn't it logically follow that at
the higher altitude the VOR would be able to be received further out?

(See AIM 1-1-8)and then order some room service! ;-)

Antonio

"Antoñio" wrote in message
news

If the FAA simply depicted a cylinder of theoretical signal strength
within the actual "semi-sphere" of service, I would completely follow the
analogy.

However, the FAA has depicted cylinders of various diameters stacked upon
each other. Given that the VOR is line-of-sight, I did not understand why,
for example, a VOR would be received 130nm out at FL180 yet only be
received 100nm at FL500. Doesn't it logically follow that at the higher
altitude the VOR would be able to be received further out?


Yes, it does logically follow that at the higher altitude the VOR would be
able to be received further out. Do you now understand why the distance is
less at higher altitude?

"Andrew Sarangan" wrote in message
1...

Isn't that the reason certain airways have a MAA - Maximum Authorized
Altitude?


Frequency overlap is probably the most common reason but they may also exist
due to conflicts with special use airspace.

I did not understand why, for example, a VOR would be received 130nm out at FL180 yet only be received 100nm at FL500. Doesn't it logically follow that at the higher altitude the VOR would be able to be received further out

Depends on the antenna radiation pattern, and interference from other
emitters.

Jose
--
Money: what you need when you run out of brains.
for Email, make the obvious change in the address.

The signal strength from a VOR decreases with distance. You are on a
straight line to the VOR from the moon but the signal strength would be too
low to create guidance.

--

Darrell R. Schmidt
B-58 Hustler History: http://members.cox.net/dschmidt1/
-

"Steven P. McNicoll" wrote in message
nk.net...

"Antoñio" wrote in message
...

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?


Yes, and every other VOR on that frequency as well. The altitude/distance
limits ensure you won't receive an unwanted VOR signal. Note that the
service volume decreases from 130 miles to 100 miles above FL 450.

"Darrell S" wrote in message
news:4R4he.25286$tQ.4405@fed1read06...

The signal strength from a VOR decreases with distance. You are on a
straight line to the VOR from the moon but the signal strength would be
too low to create guidance.


I think he was speaking figuratively, aircraft do not operate very well
outside the atmosphere.

Steven P. McNicoll wrote:


Yes, it does logically follow that at the higher altitude the VOR would be
able to be received further out. Do you now understand why the distance is
less at higher altitude?


I am not sure. Is it because the radiation pattern is spherical and not
line-of-sight?

Antonio

"Darrell S" wrote in message
news:4R4he.25286$tQ.4405@fed1read06...
The signal strength from a VOR decreases with distance. You are on a
straight line to the VOR from the moon but the signal strength would be
too
low to create guidance.

Signal is too weak to use with today's receivers, but a signal is never too
weak, with the right receiver. Look at the space robots; still in contact,
at the edge of the solar system. Amazing.
--
Jim in NC