Presently, ADS-B messages are broadcast on

  1. 1090 Mhz Mode S Extended Squitter
  2. VHF Data Link Mode-4 (VDL-4)
  3. Universal Access Transceiver (UAT) 978 Mhz

First 2 Frequencies have relevant ICAO standards and third one is predominantly used in America.

Out of the first 2, how to identify in which frequency ADS-B messages are transmitted ?

Also, Presently how many Air Traffic Control around the world use ADS-B messages as means of enforcing surveillance ?.

If installing ADS-B receivers (ADS-B IN) and relevant software are cost-efficient, (Like Flightradar24), Why many ATCs aren't making the switch and if ATC are using ADS-B messages, why do ATC still assign Squawk code ?.

  • 4
    $\begingroup$ I think you have the answer in your question for 1 and 3. 1090 MHz and 978 MHz. VHF data link operates on aircraft VHF frequencies. You might want to try a cleanup on your question to focus on a single topic at a time. $\endgroup$
    – BradHards
    Commented Jun 8, 2023 at 9:22

1 Answer 1

  1. 1090 MHz Mode S Extended Squitter. This is broadcast on 1090 MHz. It is a capability embedded in virtually all current Mode S transponders. The transponders also support Enhanced Surveillance which allows ATC to request most ADS-B data fields (AKA: BDS Registers) directly via Mode S datalink. In some areas ADS-B ground stations are used to provide ATC surveillance in areas where radar coverage is unavailable (mostly mountainous areas.)
  2. VDL Mode 4 has been in development in the northern European area (predominantly Sweden). It operates within the VHF aviation band, initially 118 MHz to 137 MHz. From a 2011 report from ICAO, the operating band has been expanded to 112 MHz to 137 MHZ. Frequencies are assigned by ATC.
  3. UAT operates on 978 MHz.

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