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Old June 13th 06, 09:38 PM posted to rec.aviation.ifr,rec.aviation.student
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Default 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