how does the to/from indicator work?

GeorgeC

GeorgeC

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I have a decent intuitive understanding of how VOR radial information is encoded in phase, but how does the ambiguity indicator work? Not how do you use it, how does it work- is it purely a function of the received radial and the OBS setting?
 
I'm curious if it is more complicated than that.

I've always assumed that it's a very simple instrument and a simple method of navigation and that it's based completely on the signal received and the OBS setting. It doesn't "know" if it's wrong, it just knows where you say you are (OBS input) and the signal received and therefore displays an indicator based on that signal source.
 
It uses Doppler. When you're flying towards the wave you are accelerating in the direction from which it is originating and so the way was compressed. When you're flying away from it it is stretched out and it uses that Plus a mathematical equation to determine whether or not the point to or from.


Edit: okay, I just made that up. I have no idea.
 
GeorgeC said:
I have a decent intuitive understanding of how VOR radial information is encoded in phase, but how does the ambiguity indicator work? Not how do you use it, how does it work- is it purely a function of the received radial and the OBS setting?
Click to expand...

When you are directly north of a station, the fixed (reference) and the variable (angle) are perfectly in phase and the zero-crossing detector says "zero phase difference". The ambiguity indicator asks, 90 degrees later, are the two signals still in phase, and if so (FROM). When you are directly south of a station, the zero crossings are STILL zero phase difference but 180° out of phase, so 90 degrees later the ambiguity meter says, "aha, one of the signals is max positive and one max negative, so (TO).

The omnibearing selector is nothing more than a continuous phase shifter that FORCES the signals to either be in phase or 180 out of phase for a centered needle. The ambiguity (TO-FROM) circuit asks the same question 90°later, still in phase (FROM) or 180 out of phase (TO).

Did that help?

Jim
 
SixPapaCharlie said:
It uses Doppler. When you're flying towards the wave you are accelerating in the direction from which it is originating and so the way was compressed. When you're flying away from it it is stretched out and it uses that Plus a mathematical equation to determine whether or not the point to or from.


Edit: okay, I just made that up. I have no idea.
Click to expand...
Edit correct. Doppler has little to do with it, but nice try. No Clinton cigar.
 
SixPapaCharlie said:
It uses Doppler. When you're flying towards the wave you are accelerating in the direction from which it is originating and so the way was compressed. When you're flying away from it it is stretched out and it uses that Pleasant mathematical equation to determine whether or not the point to or from.
Click to expand...
Note that it used the unpleasant mathematical equation until 1945 when that unpleasantness ended.
 
SixPapaCharlie said:
It uses Doppler. When you're flying towards the wave you are accelerating in the direction from which it is originating and so the way was compressed. When you're flying away from it it is stretched out and it uses that Plus a mathematical equation to determine whether or not the point to or from.


Edit: okay, I just made that up. I have no idea.
Click to expand...

hqg-2568.gif
 
SixPapaCharlie said:
It uses Doppler. When you're flying towards the wave you are accelerating in the direction from which it is originating and so the way was compressed. When you're flying away from it it is stretched out and it uses that Plus a mathematical equation to determine whether or not the point to or from.


Edit: okay, I just made that up. I have no idea.
Click to expand...
Spectacularly wrong answer. I love it!
 
It knows what radial you are actually on. Doppler, hocus pocus, internal ouiji board, I dunno, it just knows. It compares that to the "radial" you dial into the OBS. Then it puts up either TO or FROM. Actually I do know how it knows what radial you are actually on, kinda, I think. It spits out a signal every so often, in all directions. It also has a "beam" signal that rotates. It compares the "time" difference between the all directions signal and when it receives the "beam" signal. I think it does the timing thing using the phase thing.
 
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SixPapaCharlie said:
It uses Doppler. When you're flying towards the wave you are accelerating in the direction from which it is originating and so the way was compressed. When you're flying away from it it is stretched out and it uses that Plus a mathematical equation to determine whether or not the point to or from.


Edit: okay, I just made that up. I have no idea.
Click to expand...
 
LOL guys, this thread is hilarious.

But to answer the question, the VOR receiver knows the radial you are on, so it knows where you are in relation to the station. Then when you select a radial on the OBI, it determines if flying that radial would be taking you closer to or farther from the station. So yeah its simple geometry.

Edit: I found an even simpler way to state it. The receiver knows the radial you are on, it subtracts that radial from the one you selected in the OBI. If the difference is greater than 90, is shows "TO". If the difference is less than 90, "FROM". Close to 90 it shows indeterminant.
 
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Glenn D said:
I find that the Magenta Line on the new nav screen is much easier to understand... it knows the way, just stay lined up on it...
Click to expand...
Wait until you are on a SID but vectored and the controller says "direct to..." and you don't clear the previous fixes...that magenta line is all cornfused and the controller questions your parentage (or something).
 
You can actually answer this one yourself by playing with the OBS knob. Fly toward the station and tune in the reciprocal heading, and it will display from, not to.

That, in and of itself, tells you that the flag is determined by the equipment on board, and the radial is what is being interpreted by the radio signal that is received.
 
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