VHF airband

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VHF-AM aircraft band, worldwide allocation 108-137 MHz, divided into two subbands:

108.0 MHz - 117.95 MHz - aeronautical navigation only - VOR, VORTAC, localizers (50 kHz channel spacing) 117.975 MHz - 136.975 MHz - aeronautical voice and data communication, AM (25 kHz / 8.33 kHz channel spacing)

Emergency frequency 121.5 MHz is often known as GUARD CHANNEL - analogous to VHF marine channel 16 (156.800 MHz), 2182 kHz, 4125 kHz, 6215 kHz, etc.

8.33 kHz channel spacing is used in Europe and in select other locations, most of the world uses 25 kHz spacing for a total of 760 channels. VDL (VHF data link) systems such as ACARS (aircraft communications addressing and reporting system) use select frequencies in the VHF airband, including 131.550 MHz and 136.975 MHz (in the United States).

Military aircraft retain the capability to transmit and receive on the VHF-AM aircraft band, with US military aircraft radios covering up to 150.0 MHz in AM mode (25 kHz steps). Military aircraft also make extensive use of the UHF-AM aircraft band 225-400 MHz, often with ECCM systems such as HAVE QUICK, HAVE QUICK II and SATURN frequency hopping modes. The 225-400 MHz band is also extensively used for SATCOM and other purposes outside the scope of air-to-air communications. 380-400 MHz is shared with land mobile radio systems used by the US military in the United States. Military aircraft in close air support, MEDEVAC and other roles will also be equipped with VHF-FM SINCGARS tactical military radios for air-to-ground and air-to-air communications in both frequency hopping (FH) and single-channel (SC) modes.


Contents

Selected VHF aircraft frequencies

Frequency Purpose/Use
121.500 MHz Emergency Frequency known as Guard, see also 243.0 MHz - UHF Guard
121.600 MHz May be used for SAR training - practice Emergency Locator Transmitters (ELT) on a secondary basis
121.775 MHz May be used for SAR training - practice Emergency Locator Transmitters (ELT) on a secondary basis
121.950 MHz Gliders, balloons, pilot training, lighter-than-air aircraft coordination and operations
122.700 MHz UNICOM - Aeronautical Advisory Stations
122.725 MHz UNICOM - Aeronautical Advisory Stations
122.750 MHz Air-to-air communications - fixed wing aircraft
122.800 MHz UNICOM - Aeronautical Advisory Stations
122.850 MHz MULTICOM
122.900 MHz MULTICOM
122.900 MHz Secondary SAR (Search and Rescue) air-to-air/air-to-ground
122.925 MHz Coordination of forest fire suppression, fish and game management, environmental monitoring
122.950 MHz UNICOM - Aeronautical Advisory Stations
122.975 MHz UNICOM - Aeronautical Advisory Stations
123.000 MHz UNICOM - Aeronautical Advisory Stations
123.025 MHz Air-to-air communications - helicopters, also used for helicopter-to-fixed wing air-to-air coordination
123.050 MHz UNICOM - Aeronautical Advisory Stations
123.075 MHz UNICOM - Aeronautical Advisory Stations
123.100 MHz Primary SAR (Search and Rescue) air-to-air/air-to-ground, also used by Civil Air Patrol
123.300 MHz Gliders, balloons, pilot training, lighter-than-air aircraft coordination and operations
123.400 MHz Unofficial air-to-air pilot chit-chat frequency - "fingers" or "1234"
123.450 MHz Unofficial air-to-air pilot chit-chat frequency - the CB radio of the airband - also called "fingers"
123.475 MHz Unofficial air-to-air pilot chit-chat frequency
123.500 MHz Gliders, balloons, pilot training, lighter-than-air aircraft coordination and operations
126.200 MHz Common US military airfield VHF frequency (often as backup to UHF-AM and FM tactical radios)
131.550 MHz ACARS air-to-ground datalink frequency (North America)
136.975 MHz ACARS air-to-ground datalink frequency (North America)

Selected VHF aircraft sub-bands

Band Purpose/Use
118.000 MHz - 121.400 MHz Control towers
121.600 MHz - 121.925 MHz Control towers
123.600 MHz - 128.800 MHz Control towers
132.025 MHz - 135.975 MHz Control towers

8.33 kHz channels vs. 25 kHz channels

In countries using the legacy 25 kHz channel plan, VHF frequencies are (were) often referred to by the frequency in MHz followed by the two digits after the decimal. For example, 129.175 MHz would be called "129.17 - as in one two niner decimal one seven" and 123.425 MHz would be called "123.42 or one two three point four two". With 25 kHz channel spacing, there's no need to read the third digit, as it is always a 5 on the 1xx.x25 or 1xx.x75 frequencies. 124.1 MHz would obviously be one two four point one and 133.95 would be one three three point niner five or one three three decimal niner five.

In areas using the narrower 8.33 kHz spacing, things become a little more complicated. Due to the number of digits after the decimal point on the 8.33 kHz channels, a rounding system has been developed. Instead of reading the entire frequency, aircraft radio displays round the channel up or down to the nearest 5 kHz channel (so 120.00833 MHz becomes 120.010 MHz, etc.)

This gets even more insane when you include the old 25 kHz channels in the 8.33 kHz channel plan. Therefore, you must know if your radio is in 25 kHz mode or 8.33 kHz mode. For example, on a 25 kHz radio, 118.025 MHz shows on the display as 118.025 MHz (or 118.02 MHz). On a radio switched to 8.33 kHz mode, 118.025 MHz shows on the display as 118.030 MHz... The lunacy is pretty apparent here. Instead of switching from 25 kHz steps to 8.33 kHz steps, the switch should have been from 25 kHz steps to 12.5 kHz steps or 5 kHz steps.

  • 118.0000 MHz - 118.000 MHz [display frequency]
  • 118.00833 MHz - 118.010 MHz [display frequency
  • 118.0166 MHz - 118.015 MHz [display frequency]
  • 118.025 MHz - 118.030 [display frequency]
  • 118.0333 MHz - 118.035 MHz [display frequency]
  • 118.0416 MHz - 118.040 MHz [display frequency]
  • 118.050 MHz - 118.055 MHz [display frequency]
  • 118.0583 MHz - 118.060 MHz [display frequency]
  • 118.0666 MHz - 118.065 MHz [display frequency]
  • 118.075 MHz - 118.080 MHz [display frequency]
  • 118.0833 MHz - 118.085 MHz [display frequency]
  • 118.0916 MHz - 118.090 MHz [display frequency]
Icom IC-A210E VHF-AM airband transceiver, designed for installation in aircraft, this version of the IC-A210 supports the 8.33 kHz narrowband channel spacing required in Europe. Frequency coverage is 118.000 MHz to 136.975 MHz in 25 kHz or 8.33 kHz steps with 6 watts AM carrier power.

Some frequencies will not be switched over to 8.33 channeling. The obvious one is 121.5 MHz - the aircraft emergency frequency.


NAV Navigation VHF VOR

The 108 MHz - 117.95 MHz band is allocated for navigation signals, including the VHF Omnidirectional Range - VHF Omni Range or VOR, the Instrument Landing System (ILS) localizer transmitters (localizers operate within the 108.100-111.950 MHz band and are paired with the UHF glideslope transmitters operating in the 328.600-335.400 MHz band, see chart below). Aircraft navigation systems use numerous other frequency bands, ranging from LF/MF up through UHF and SHF.


See also:



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