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I cannot find an official, trustworthy source on the bandwidth of the 1090 Mode S extended squitter ADS-B signal. It is not even listed in DO-260C standard. I've seen ranges from 50 kHz to 11 MHz (https://www.komachine.com/en/companies/ap-satellite/products/53719-ADS-B-(Automatic-Dependent-Surveillance-Broadcasting)-System). SigID Wiki claims 2 MHz in the US (https://www.sigidwiki.com/wiki/Automatic_Dependent_Surveillance-Broadcast_(ADS-B)), but I've also seen 1.3 MHz.

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    $\begingroup$ You have to define and be consistent about what you mean by "bandwidth." Theoretically, the absolute bandwidth of most signals are infinite. There are various definitions: -3 dB, -10 dB, -20 dB, -40 dB, and non-linear definitions (spectral channel masks). The latter is what most standards, including ICAO defines. $\endgroup$
    – user71659
    Oct 21, 2022 at 20:41
  • $\begingroup$ @user71659 OK, I agree with you. Most times we use 3dB bandwidth, but you indicate a spectral mask is used in this case/purpose. How does that help if I do not see the signal or the mask in any documentation. $\endgroup$
    – Macuser
    Oct 22, 2022 at 10:00

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The bandwidth is not specified in the ADS-B MOPS as the 1090ES transmitter is defined in the Mode S MOPS.

Here is the graphical description of the required transmitter bandwidth from the ICAO SARPS:

Mode S spectrum limits.

The transmitted data is within the 2.6 MHz, -3dB portion.

The raw data rate of the extended squitter is 1 Mb/sec. The data is encoded using pulse position modulation (PPM). In PPM encoding, there is a 1 microsec slot for each bit with a 1/2 microsec pulse located in either the first or second half of the slot to indicate a 1 or 0, respectively. As the pulses are a 1/2 microsec in width, the necessary bandwidth is 2 MHz.

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  • $\begingroup$ Yep, you are correct. The spectral mask information is located in DO-181F. Thanks. $\endgroup$
    – Macuser
    Oct 23, 2022 at 14:53
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As shown by the SigID Wiki page you linked, 1090 MHz ADS-B (the international version) has a bandwidth of 2 MHz. The 1.3 MHz version operates on 928 MHz and is only used in the United States.

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  • $\begingroup$ UAT is not the same as 1090ES ADS-B. $\endgroup$
    – Macuser
    Oct 22, 2022 at 9:59
  • $\begingroup$ UAT carries ADS-R, TIS-D and FIS(weather and notam). Of those only TIS is available by relay on 1090ES. $\endgroup$ Oct 22, 2022 at 17:19

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