azeem
Topic Author
Posts: 132
Joined: Mon Jul 03, 2000 8:17 pm

Hi there

Can anyone please provide information on radials. How to intercept them and how to set courses etc.

Thanks

Guest

I think I have covered everything!
Iain

Guest

Azeem,

I found this one web site that simulates an airplane flying around with 2 VOR stations. You can position the airplane and the stations in various ways and observe how the needles behave. It is a great learning tool. Check it out:
http://www.visi.com/~mim/nav/

Best regards,
Nut

Buff
Posts: 1066
Joined: Fri Mar 16, 2007 1:29 pm

Nut: GREAT site for beginners. Well done! I was going to make a post on this last night for Azeem but was too tired.

If I could add to what you and Iainhol have posted, one of the biggest difficulties beginners have with VOR/ADF navigation is visualizing where they are relative to the transmitting station, be it a VOR or an NDB. When dealing with VOR's one is dealing with "Radials" which one also has the benefit of a visual tool, i.e. the VOR display. With the ADF which tracks NDB's with a needle pointer, the exercise is quite a bit more difficult, especially with an older fixed-card ADF (do they even have those things anymore?), or worse, a drum style DG!!

Back to Radials: One of our avionics experts could give a better technical explanation, but I'll give a layman's view here on what they are, how they're created and received and how to "track" one.

How: Each VOR station radiates a couple of signals in a slightly out of phase condition. One of these signals is an omnidirectional signal going out in all directions; the other is a uni-directional signal that is rotated in direction (somebody said) 30 times a second, moving from 000 degrees to 359 degrees 30 times a second. As the moving signal reaches 000 degrees, both signals overlap and are "in-phase"; as the uni-d signal continues to 090, the two signals are then 90 degrees out of phase; at 180, 180 degrees out of phase. Then as it continues to 270, the signal is only 90 degrees out of phase decreasing to 0 at OOO. They can only be out of phase at a maximum of 180 degrees. Any more or less makes them + or - out of phase. That's why at the 270 radial, it's only 90 degrees out. Make sense? The VOR receiver in the airplane translates this phase measurement into something you can see and interpret - the VOR needle and the TO/FROM indicator - the two of three things you need to navigate. The TO/FROM indicator lets you know the orientation of the "out-of-phase" or +/- condition mentioned above.

Using the information: First thing that needs to be done is to tune and identify the transmitting station. As it's a VHF signal, it's restricted to line of site. At 6,000' of altitude, you can expect about about 90 miles of reliable range. The identification is by either morse code (published on charts) or voice identification and almost always in a three-letter format. This identification can't be stressed enough as more than once you will mis-tune and end up using the wrong signal - a recipe for disaster.

Second is to determine where you are relative to the VOR. A "radial" is ALWAYS identified on a VOR receiver as a FROM indication with the needle centred. ALWAYS a FROM indication - remember that for as long as you're in aviation. Very, VERY important if you are just learning.

If you use the site that Nut links us to above, you can move the little airplane around and then spin the associated VOR needle until it centres and gives you a FROM indication. A picture is worth a million words. When you get that indication, then you can do the same thing with the other VOR needle and notice a different FROM indication with the needle centred. If you then plot these two radials on a map, they will intersect and that is where you are on the map.

That's the first step in navigating. Know where you are starting from. And that's the basics of learning the VOR.

I'm going to stop here and wait for a response from Azeem to see if this makes sense. If it doesn't, then saying anything else will cause more confusion!!

Let me know!

Best Regards,

Buff

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