Look guys, my handicap is years of experience training aircraft mechanics, pilots and dispatchers. I have to be able to tell them things in a way they can understand
and not just memorize. I think excessive reliance on memory is contrary to safety of flight. This is one of those places where the FAA and I agree.
I believe that the way a radio altimeter works is based on an underlying constant - the speed of light. So a beam goes out. A beam bounces back. Some mechanism determines how long that took. That yields the distance to the surface. One mile out and one mile back equals one "radar mile" or 10.75 microseconds.
That is how it works.
Now as an instructor and as a technical writer I have to make it comprehensible without falsifying it.
you wrote "So, there is no time measurement nor even a time reference, but of course time is the underlying fixed factor"
Now how can I explain that to students? That time is the underlying factor but we IN
NO WAY measure it? So you are saying that the frequency modulation changes could be utterly random, that they could vary at random rates, or not at all and we could still tell how far the signal traveled?
Look guys, just because no one looked at their Rolex doesn't mean timing did not occur.
I have a different problem with your analogy. Picture me putting that up in front of students, who are not fools. A hand goes up.
"Captain Slam I assume the pulley at the bottom is the surface, but is the pulley at the top the airplane?"
"No, the airplane is my finger somewhere in the middle."
"Okay, then, WHAT IS the pulley at the top? Do they have transmitters hanging in the sky?"
I submit to you that the pulley at the top
is the constant - the speed of light. There is just no way you can make this work without measuring time. You may measure it by knowing electronic or mechanical rates of change, but those are just details. The underlying truth that makes it work is the speed of light.
In recent years there has been a trend in training US airline pilots, away from so-called "nuts and bolts" type of courses. I have mixed feelings about this because of my own mechanical background but they sign my paycheck I teach the way they want it. If a student comes to me during the break and wants to know more I'll try to accommodate.
So how does a radio altimeter work?
25 words or less.
Whatever the electro-mechanical minutiae in the details of how it is done, the simple answer (and not incorrect) is "We know how long it takes for a radio signal to travel a distance and bounce back."
If I'm teaching someone how to calibrate a radio altimeter - well, I would not be doing that because I am not qualified, never going to be qualified. But this student should get the full "nuts and bolts" of how it works.
For pilots and lay people, it is the speed of light, the radar mile. That depends on our ability to quantify the passage of time. Some people call that timing, no matter how it is accomplished.
Happiness is not seeing another trite Ste. Maarten photo all week long.