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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 ?.

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    $\begingroup$ 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
    Jun 8, 2023 at 9:22

1 Answer 1

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  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.

As ASE is based on a one question-one answer concept, please post your other questions separately.

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