The four course low-frequency range was an effective tool for its time. In an era when electronic equipment was expensive, it allowed one to navigate with a whiskey compass, a clock and an AM radio that could receive the signals (below the AM broadcast band). It had its disadvantages, though. All one received was the audio signal, which told a pilot that he was left of course, right of course or on course. It did not tell you where you were in relation to the station. Orienting one's self if one were truly lost in the clouds was a daunting task. And if the weather was such that it interfered with clear reception on the AM band, then one could be well and truly screwed.
The answer to that was the Very High Frequency Omnidirectional Radio Range, "Omni" or "VOR". This is a VOR station:
A VOR broadcasts a nearly infinite radial bearing by some magic of some kind. The VOR broadcast band is just above the FM radio broadcast band. A VOR station is indicated on sectional charts by a blue circle that is 20NM in diameter. You can see one in the upper left corner of this chart:
VOR radials are always described as the bearing from the VOR station, so if you are on the 300 radial of any given VOR, you are northwest of the station. The radials are aligned to the magnetic north pole as of the time the station was commissioned.
To use one, the first thing you should do is turn the Omni-navigational Bearing Selector, or "OBS" to a bearing that is near the one you are on.
The reason to do that is because if the bearing is way off from where you are, when you tune the VOR receiver in, the needle will slam to one side or the other and that is not a good thing. You then tune in the VOR receiver (they're all digital nowadays) to the correct frequency. If you are in range, the needle should twitch a little and, in the illustration above, the red/white crosshatch should change to a reading of either "to" or "from" (more on that later). Then you should turn up the volume knob on the VOR receiver and listen for the identifier for the station to ensure you are tuned into the correct one. The identifier is typically a three digit Morse code identifier and since most pilots do not know Morse code, the actual isgnal is printed in the information block for the station. (The VOR station on the chart is Topeka, or "TOP," - --- .---)
As I said, radials are bearings from the VOR station. If you are on a 300 bearing from the station and you set the OBS to 30, the needle will center and the little box where the red and white crosshatch is will show a "from" flag. But you probably want to fly towards the station, so you turn the OBS until 12 is at the top and the OBS flag will read "to." If you are flying towards the station, you want to see a "to" and if you are flying away from the station, you want to see a "from." The reason for this is the bearing needle will point towards the centerline of the radial bearing if you are not on it; if you are flying to the station with a "from" indication, the needle will "reverse sense" and point away from the radial.
By either tuning back and forth between two stations or by using a second VOR receiver, you can receive bearings from two stations and determine your position.
But that is not all VOR stations can do. This is the information box for the Topeka VOR:
117.8 MHz is the frequency of the VOR itself. The channel number is the TACAN channel, which is of interest to the military. Above the box is a voice frequency of 122.45 MHz and below the box is the word "Wichita." You can tune your voice radio to 122.45 to call the Wichita Flight Service Station ("Wichita Radio" is the call sign) for weather updates, to file change or cancel flight plans or to submit a weather report. If the frequency above the box says "122.1R, then you transmit to FSS on 122.1 and listen on the VOR frequency itself. Any given FSS is monitoring a lot of VOR outlets; good form is to call the FSS, give your call sign and say which VOR you are calling through.Now go back up to the chart itself, you will see blue lines running between some of the VOR stations. Those are the airways themselves. Airways at or below 18,000 feet are designated by the letter "V" and a number; they collectively are known as the Victor airways. If airways combine, both numbers are used. Victor 502 and Victor 10-12 can be seen on the chart. High altitude charts, used above 18,000 feet, are J-airways ("J" for "jet"). There is no real requirement for VFR flights to use the airways. IFR flights fly the airways and have for decades, though there is a move to get away from those routings.
VORs are stil in wide use, though the Feds would love to get away from the cost of maintaining all of the VOR stations. Concerns about what will happen to the GPS satellites in a severe solar storm are some of the factors that may keep VORs around for awhile yet.
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