CFII oral exam guide questions?

Well, Jim, it almost COULD work that way, but it doesn't. :-[
VOR azimuth angle is measured by a phase comparison
between two sinusoidal signals, not a time-delay measurement.
The VOR reference signal is frequency modulated on a subcarrier,
while the azimuth signal is from amplitude modulation on the
radio-frequency carrier, caused by the VOR's rotating cardioid beam.

Separately, DME distance is measured radar-like, by the time it takes
for the ground transponder to *reply* with a delayed pulse-pair
to an interrogation transmitted from the aircraft.

"Jim Macklin" wrote in message news:vhDjg.137276$k%3.119945@dukeread12...
You can explain how a VOR/DME works with a simple visual
model.

There is a large lake with an island in the middle. There
is a lighthouse with a rotating beacon that makes one
revolution a minute. It has a white beacon and a green
beacon, when the white beacon is passing North, a big strobe
light on top flashes and a very loud horn sounds.

You see the strobe light flash and 6 seconds later see the
green beacon sweep by. Where are you? 216 degrees from the
beacon. Ten seconds after the strobe, you hear the horn,
how far away? 2 miles.

VOR is the same, just faster.

--
James H. Macklin
ATP,CFI,A&P

Well, Jim, it almost COULD work that way, but it doesn't. :-[
VOR azimuth angle is measured by a phase comparison
between two sinusoidal signals, not a time-delay measurement.
The VOR reference signal is frequency modulated on a subcarrier,
while the azimuth signal is from amplitude modulation on the
radio-frequency carrier, caused by the VOR's rotating cardioid beam.

It's indirect, but isn't a measurement of phase difference of two
different waves the same as the measurement of the time difference
between crests (once you take into account the frequency and the speed
of light)? It's like saying the alimiter measures altitude. It's not
technically correct (and yes, the difference is meaningful under some
circumstances) but gets the job done.

Jose
--
The price of freedom is... well... freedom.
for Email, make the obvious change in the address.

"Jose" wrote in message . com...
Well, Jim, it almost COULD work that way, but it doesn't. :-[
VOR azimuth angle is measured by a phase comparison
between two sinusoidal signals, not a time-delay measurement.
The VOR reference signal is frequency modulated on a subcarrier,
while the azimuth signal is from amplitude modulation on the
radio-frequency carrier, caused by the VOR's rotating cardioid beam.

It's indirect, but isn't a measurement of phase difference of two
different waves the same as the measurement of the time difference
between crests (once you take into account the frequency and the speed
of light)? It's like saying the alimiter measures altitude. It's not
technically correct (and yes, the difference is meaningful under some
circumstances) but gets the job done.

Jose
--


The time domain and the frequency domain are related conventionally
through a mathematical manipulation called the Fourier Transform.
However, the measurement methods used in the two domains
are considerably different.
The VOR system was designed for measurements in phase space.
DME, of course, was designed for the time domain.

too difficult to comprehend for the beginning student who is not an
electronics major

BT

"John R. Copeland" wrote in message
.. .
"Jose" wrote in message
. com...
Well, Jim, it almost COULD work that way, but it doesn't. :-[
VOR azimuth angle is measured by a phase comparison
between two sinusoidal signals, not a time-delay measurement.
The VOR reference signal is frequency modulated on a subcarrier,
while the azimuth signal is from amplitude modulation on the
radio-frequency carrier, caused by the VOR's rotating cardioid beam.

It's indirect, but isn't a measurement of phase difference of two
different waves the same as the measurement of the time difference
between crests (once you take into account the frequency and the speed
of light)? It's like saying the alimiter measures altitude. It's not
technically correct (and yes, the difference is meaningful under some
circumstances) but gets the job done.

Jose
--


The time domain and the frequency domain are related conventionally
through a mathematical manipulation called the Fourier Transform.
However, the measurement methods used in the two domains
are considerably different.
The VOR system was designed for measurements in phase space.
DME, of course, was designed for the time domain.

The time domain and the frequency domain are related conventionally
through a mathematical manipulation called the Fourier Transform.

That may be true, but is also a ten dollar irrelevancy. The phase
difference directly relates to the time difference. Operationally, the
circiuitry employs phase relationships rather than a little man with a
fast stopwatch, but new pilots attempting to understand the concept of
VOR navigation don't need to understand RF electronics to "get" the idea
behind the VOR, especially in contrast to the ADF or DME. I find the
analogy completely apt.

The VOR system was designed for measurements in phase space.
DME, of course, was designed for the time domain.

This is a useful distinction for ciruit designers, but not for new pilots.

Jose
--
The price of freedom is... well... freedom.
for Email, make the obvious change in the address.

In article ,
Jose wrote:

The time domain and the frequency domain are related conventionally
through a mathematical manipulation called the Fourier Transform.

That may be true, but is also a ten dollar irrelevancy. The phase
difference directly relates to the time difference. Operationally, the
circiuitry employs phase relationships rather than a little man with a
fast stopwatch, but new pilots attempting to understand the concept of
VOR navigation don't need to understand RF electronics to "get" the idea
behind the VOR, especially in contrast to the ADF or DME. I find the
analogy completely apt.

I honestly don't see why a pilot needs to know anything beyond, "A VOR
transmits 360 radials, and the NAV receiver can tell which one you're on".

Unlike some of the physics half-truths the FAA pushes, I can't see how this
little white lie could possibly get you into any operational trouble. It
doesn't get in the way of understanding VOR declination, or service
volumes, or scalloping due to signal reflections, or reverse sensing, or
the zone of confusion, or any of a number of little VOR gotchas that pilots
do need to be aware of.

"Roy Smith" wrote in message ...

I honestly don't see why a pilot needs to know anything beyond, "A VOR
transmits 360 radials, and the NAV receiver can tell which one you're on".

Unlike some of the physics half-truths the FAA pushes, I can't see how this
little white lie could possibly get you into any operational trouble. It
doesn't get in the way of understanding VOR declination, or service
volumes, or scalloping due to signal reflections, or reverse sensing, or
the zone of confusion, or any of a number of little VOR gotchas that pilots
do need to be aware of.

This is usenet so we like to split hairs. :-)
VORs are not limited to "360 radials".
If you want to claim you navigate to 1/2-degree precision, or finer, VORs do that.
Personally, I try not to claim that ability, though. :-/

"Jose" wrote in message . com...
The time domain and the frequency domain are related conventionally
through a mathematical manipulation called the Fourier Transform.

That may be true, but is also a ten dollar irrelevancy. The phase
difference directly relates to the time difference. Operationally, the
circiuitry employs phase relationships rather than a little man with a
fast stopwatch, but new pilots attempting to understand the concept of
VOR navigation don't need to understand RF electronics to "get" the idea
behind the VOR, especially in contrast to the ADF or DME. I find the
analogy completely apt.

The VOR system was designed for measurements in phase space.
DME, of course, was designed for the time domain.

This is a useful distinction for ciruit designers, but not for new pilots.

Jose
--

Jose, you asked and I answered. I didn't disagree with you.
The truth is out there for those who are interested.
But Jim's DME explanation was egregiously wrong, and shouldn't propagate.