Tutorial VOR

Tutorial: VOR (radial from a navigation beacon)

What it is

A VOR is a ground beacon between 108 and 118 MHz that tells an aircraft its bearing from the station. Each station also sends a Morse code identification and sometimes voice. OnAir measures the radial you are on, reads the identification, and with two stations can estimate a position. It is a learning and monitoring tool: do not use it for navigation.

What you need

• A radio that tunes 108 to 118 MHz. The mode asks for 2 Msps; the lowest working rate is 100 ksps (the channel width in the mode table is 50 kHz). An RTL-SDR works. See Supported radios.
• A VHF antenna. VOR signals are line of sight; stations are strong near airports and weaker at range. Vertical polarisation is not required for VOR; a horizontal or any VHF antenna works.
• Frequencies: the database lists the band edges (VOR 108.000 to 117.950 MHz; "even tenths below 112 are ILS localizers"). The actual station frequency for your area comes from an aeronautical chart or navaid database. The mode starts at 113 MHz.

Before you start

• You need to be reasonably near a station, often within 50 to 100 km on the ground, further when high.
• A station list makes the Stations view and the position fix more useful; see step 4.

Step by step

1. Choose the group Aviation, entry Radial, 108-118 MHz (mode VOR).
2. Type the station's frequency into the tuner and press Start. The status reads "receiving" and shows the carrier.
3. The Radial view shows the radial and the ident. The status says whether the beacon is a conventional VOR or a Doppler VOR, which the decoder detects.
4. In Stations, press Import CSV... and load a station list. OnAir does not bundle one; the panel names two public sources (OurAirports navaids, public domain, and OpenAIP, non-commercial licence) and you download the file yourself.
5. For a position, open Fix: enter two station frequencies in the rows A and B (MHz, 108.00 to 117.95), press tune for each, or tick hop between A and B with a dwell of 4 to 30 seconds. When both radials are read and both stations are identified and in the list, a position, a 95 percent error ellipse and the angle between the two radials appear on a map.

What you should see

A steady carrier, a radial angle in degrees with a plus-or-minus value, and a Morse ident decoded as letters (three letters, repeated about every 30 seconds) once it has been keyed. Voice on a VOR is announcements by the station and is heard as audio.

Reading the screen

• Radial: the current radial, a history of the last two minutes, the carrier level, FM deviation, subcarrier and tones, and the identification.
• Fix: described above; "waiting for both radials" until both have been read.
• Stations: the imported list with name, ident and type; a search box filters by ident or name; entries are marked "not in the station list on this frequency" if the frequency is unknown.
• scan: a list of frequencies in MHz to hop through; after a pass it lists what each one hears ("no VOR" where nothing).

Options and settings

An ident filter takes the 1020 Hz identification out of the voice. Positions use true bearings and need the station list; check the panel for how the radial is referenced.

Troubleshooting

• "no VOR signal" or "no carrier": wrong frequency, or too far from the station.
• Radial jumps: reflections; try another antenna position. Near buildings the radial can be off by several degrees.
• Ident missing: wait up to 30 seconds; the ident is keyed on a long cycle.
• Fix needs both stations "identified and in the list": import a list and let the ident decode.

Tips

Use scan to find which VORs you can hear from home before you set up a fix.

Legal and privacy notes

VOR beacons are public navigation aids; receiving them is unrestricted in most countries. Never rely on OnAir for navigation or flight; it is not certified. See Legal.

Under the hood

A VOR carrier is amplitude-modulated with a 30 Hz variable signal and a 9960 Hz subcarrier frequency-modulated with a 30 Hz reference; the radial is the phase difference between the two 30 Hz signals. Doppler VOR swaps the roles of reference and variable. The identification is a 1020 Hz tone keyed in Morse. Specified in ICAO Annex 10 vol. I.

Related

VOR mode page, Tutorial: ILS, Tutorial: NDB, Tutorial: Airband.