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.
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 MHz in AM mode. 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.
Selected VHF aircraft frequencies
|121.500 MHz||Emergency Frequency known as Guard, see also 243.0 MHz - UHF Guard|
|122.900 MHz||Secondary SAR (Search and Rescue) air-to-air/air-to-ground|
|123.100 MHz||Primary SAR (Search and Rescue) air-to-air/air-to-ground, also used by Civil Air Patrol|
|123.450 MHz||Unofficial air-to-air pilot chit-chat frequency|
|123.475 MHz||Unofficial air-to-air pilot chit-chat frequency|
|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)|
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.
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.
- 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]
- 136.98333 MHz
- 136.99166 MHz
- 137.0000 MHz
Some frequencies will not be switched over to 8.33 channeling. The obvious one is 121.5 MHz - the aircraft emergency frequency.
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