VHF airband

From HFUnderground

Revision as of 13:03, 24 May 2024

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/glideslope (ILS) (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).

VHF aircraft communications originated during the Second World War. German air-to-ground communications networks, various radar systems (eg. Chain Home) operated in what is now called the VHF low band (roughly 35-48 MHz). American air to air and air-to-ground systems started transitioning from MF/HF to VHF-AM (100 to 156 MHz, usually crystal controlled radios with pushbutton channel selection) during the war. The 100 to 156 MHz band was only used during the war, with the narrower 108-135 MHz band being adopted shortly thereafter. Originally 100 kHz steps, followed by 50 kHz steps, then the expansion of the band up to 136.000 MHz, then eventually 136.975 MHz and 136.99167 MHz (136.995 MHz) or 137 MHz. Military aircraft have maintained capability to operate above 137 MHz for air to air tactical communications. Coverage extends up to 150.8 MHz (officially).

Military aircraft retain the capability to transmit and receive on the VHF-AM aircraft band, with US military aircraft radios covering up to 150.8 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.

Common VHF Aircraft Frequencies

• 121.500 MHz - Emergency - Guard 121.5 MHz
• 123.100 MHz - SAR On Scene Common Use 123.1 MHz, including Civil Air Patrol
• 122.925 MHz - Special Use, Government Resource Management Multicom 122.925 MHz 122.92 MHz
• 122.900 MHz - Multicom, SAR training and secondary 122.9 MHz
• 122.950 MHz - Unicom - Controlled Airports - Traffic Advisory For Towered Airports
• 122.850 MHz - Multicom 122.85 MHz
• 122.200 MHz - Flight Watch or FLIGHTWATCH (merged with 122.0 MHz network) 122.2 MHz
• 126.200 MHz - MILCOM - Military airports, advisory frequency 126.2 MHz
• 134.100 MHz - MILCOM - Military airports, advisory frequency 134.1 MHz
• 123.975 MHz - VHF AM "Victor" National Firefighting Use
• 132.450 MHz - VHF AM "Victor" Flight Following - VHF National Flight Following 168.650 MHz 110.9Hz PL
• 122.700 MHz - Unicom - Uncontrolled Airports
• 122.725 MHz - Unicom - Uncontrolled Airports
• 122.775 MHz - Unicom - Uncontrolled Airports
• 122.800 MHz - Unicom - Uncontrolled Airports
• 122.975 MHz - Unicom - Uncontrolled Airports
• 123.000 MHz - Unicom - Uncontrolled Airports
• 123.025 MHz - Unicom - Uncontrolled Airports - air to air traffic advisory frequency in some areas 123.02 MHz
• 123.050 MHz - Unicom - Uncontrolled Airports - air to air traffic advisory frequency in some areas 123.05 MHz
• 123.075 MHz - Unicom - Uncontrolled Airports - air to air traffic advisory frequency in some areas 123.07 MHz
• 121.950 MHz - Gliders and balloons, air-to-air and air-to-ground
• 123.300 MHz - Gliders and balloons, air-to-air and air-to-ground - flight training frequency
• 123.500 MHz - Gliders and balloons, air-to-air and air-to-ground - flight training frequency - balloons and some gliders also use VHF/UHF Business Band frequencies
• 123.325 MHz - Air To Air / Air To Ground - Blimp Operations (other frequencies used, including on the VHF/UHF Business Band)
• 122.750 MHz - Air To Air official fixed wing air-to-air frequency 122.75 MHz
• 123.025 MHz - Air To Air 123.025 MHz 123.02 MHz
• 123.400 MHz - Air To Air "Fingers" 123.4 MHz
• 123.450 MHz - Air To Air "Fingers" or interplane - officially used for air to air over oceans 123.45

Long Range VHF Networks

Including the ARINC wide area long range FL20 and above network, 129.9 MHz, 130.7 MHz, etc.

• 123.450 MHz - International Air to Air 123.45 MHz
• 129.400 MHz - San Francisco VHF - Long Range, multiple remote sites 129.4 MHz
• 131.950 MHz - SFO ARINC Long Range 131.95 MHz
• 129.900 MHz - ARINC New York Area - JFK
• 129.400 MHz - ARINC New York Area - LGA
• 129.900 MHz - MARITIMENET - U.S. East Coast - 20,000 feet and up FL20 and higher 129.9 MHz
• 130.700 MHz - MEXNET and GULFNET - Gulf Coast, Gulf of Mexico - 20,000 feet and up FL20 130.7 MHz
• 128.900 MHz - ARINC En Route Service - Southwest USA 128.9 MHz
• 129.400 MHz - ARINC En Route Service - Northeast USA / Great Lakes Area / Canada West Coast and Anchorage Alaska 129.4 MHz
• 129.450 MHz - ARINC En Route Service - East Central USA 129.45 MHz
• 131.800 MHz - ARINC En Route Service - Northwest USA 131.8 MHz
• 129.900 MHz - ARINC Maritime Net (Northeast Coast USA) 129.9 MHz (see MARITIMENET)
• 130.700 MHz - ARINC Mexico / Caribbean - 130.7 MHz (see MEXNET and GULFNET)
• 131.175 MHz - ARINC En Route Service - Southeast USA 131.175 MHz 131.17 MHz
• 130.400 MHz - ARINC En Route Service - West Central USA 130.4 MHz
• 131.950 MHz - ARINC Pacific Net (West Coast USA and Hawaii) 131.95 MHz

VHF ACARS Data Frequencies

• 129.350 MHz - Wide Area Coverage (En Route)
• 131.475 MHz - Wide Area Coverage (En Route) - Air Canada (DataPlus Network)
• 136.850 MHz - Wide Area Coverage (En Route)
• 136.950 MHz - Wide Area Coverage (En Route)
• 136.975 MHz - Wide Area Coverage (En Route)
• 128.975 MHz - Terminal Base Station Links At Airports
• 130.875 MHz - Terminal Base Station Links At Airports
• 131.000 MHz - Terminal Base Station Links At Airports
• 131.650 MHz - Terminal Base Station Links At Airports
• 131.725 MHz - Terminal Base Station Links At Airports

Selected VHF aircraft sub-bands

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:

• HF aircraft bands HF aeronautical frequencies