[HN Gopher] The 1090 Megahertz Riddle: A Guide to Decoding Mode ...
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The 1090 Megahertz Riddle: A Guide to Decoding Mode S and ADS-B
Signals
Author : toomuchtodo
Score : 71 points
Date : 2025-08-03 18:54 UTC (3 days ago)
(HTM) web link (books.open.tudelft.nl)
(TXT) w3m dump (books.open.tudelft.nl)
| toomuchtodo wrote:
| DOI: https://doi.org/10.34641/mg.11
|
| Source files/code: https://mode-s.org/
|
| Synopsis:
|
| In the last twenty years, aircraft surveillance has moved from
| controller-based interrogation to automatic broadcast. The
| Automatic Dependent Surveillance-Broadcast (ADS-B) is one of the
| most common methods for aircraft to report their state
| information like identity, position, and speed. Like other Mode S
| communications, ADS-B makes use of the 1090 megahertz transponder
| to transmit data. The protocol for ADS-B is open, and low-cost
| receivers can easily be used to intercept its signals. Many
| recent air transportation studies have benefited from this open
| data source. However, the current literature does not offer a
| systematic exploration of Mode S and ADS-B data, nor does it
| explain the decoding process.
|
| This book tackles this missing area in the literature. It offers
| researchers, engineers, and enthusiasts a clear guide to
| understanding and making use of open ADS-B and Mode S data. The
| first part of this book presents the knowledge required to get
| started with decoding these signals. It includes background
| information on primary radar, secondary radar, Mode A/C, Mode S,
| and ADS-B, as well as the hardware and software setups necessary
| to gather radio signals. After that, the 17 core chapters of the
| book investigate the details of all types of ADS-B signals and
| commonly used Mode S signals. Throughout these chapters, examples
| and sample Python code are used extensively to explain and
| demonstrate the decoding process. Finally, the last chapter of
| the book offers a summary and a brief overview of research topics
| that go beyond the decoding of these signals.
|
| (books is open/freely available for download)
| fluxquanta wrote:
| > aircraft surveillance has moved from controller-based
| interrogation to automatic broadcast
|
| I'd take issue with the phrasing "moved from" and would rather
| use "supplemented by". Controller-based interrogation is still
| widely used.
| touisteur wrote:
| Moreover the advantage of Mode S radar (ground-initiated
| transactions) is that you're using a self-coherent system:
| the radar knows what it sent and what it is supposed to
| receive, and when, in a narrow beam, etc.
|
| It makes lots of spoofing attacks unpractical. Where as
| relying on GNSS exposes to a whole bunch of 'constellation
| replay' or fake-adsb-telegrams attacks. Mode S lacks
| authentication, but there's no reason it couldn't be tacked
| on one day (through e.g. the already available 'advanced'
| data-link capabilities or the many available 'gicb'
| registers...). Even light session-authentication would break
| most of the remaining spoofing attacks (and most swap
| problems) on ground-initiated Mode S radar.
| jjwiseman wrote:
| Great book that I reference all the time.
|
| (The title is actually "The 1090 Megahertz Riddle".)
| toomuchtodo wrote:
| It appears that was clipped when I submitted. I will email the
| mods and request they correct the title. Thank you.
| tomhow wrote:
| Fixed, thanks!
| willwade wrote:
| I'll save someone the googling since I just did. You need some
| hardware to hack: I think this is what you need: https://www.rtl-
| sdr.com/buy-rtl-sdr-dvb-t-dongles/
| toomuchtodo wrote:
| Related:
|
| https://www.adsbexchange.com/ways-to-join-the-exchange/build...
|
| https://www.adsbexchange.com/open-source-software/
|
| https://old.reddit.com/r/raspberry_pi/comments/157wd9t/here_...
| Catbert59 wrote:
| Better also add a SAW bandpass and a properly designed
| amplification (LNA) stage to this.
|
| The RTL-SDRs are great - but heavily limited in their dynamics
| (8 Bit ADC). They get deaf quickly if you are located next to
| strong transmitters like FM/DAB/DVB-T/etc.
|
| Aliexpress has cheap antennas that include all of this.
| pests wrote:
| Hey, mind looking up a link to one of those antennas? Just
| don't want to pick the wrong part, so many abbreviations and
| acronyms.
|
| I picked up an rtl sdr about a year or two ago and haven't
| done much outside of listening to local FM stations.
|
| Would be fun to go a bit deeper. Track satellites or listen
| to boats/ planes / etc.
| Catbert59 wrote:
| https://de.aliexpress.com/item/1005009311806479.html
|
| Plus
|
| https://de.aliexpress.com/item/1005009237905498.html
|
| Maybe you can find an antenna with both integrated.
| ap-andersson wrote:
| If you want an easy to use project to get a map and feed to
| different sites like adsbexchange and flightradar24, I would
| recommend checking out: https://github.com/sdr-enthusiasts
| https://github.com/sdr-enthusiasts/docker-adsb-ultrafeeder
| https://github.com/sdr-enthusiasts/docker-flightradar24
| https://adsb.im/home
|
| There is a good community out there on github and discord that
| have flight tracking as a hobby. In addition to ADS-B there is
| also voice radio transmissions from aircraft (airband) and text
| messages (ACARS) etc. If you get hooked there is lots of
| different things to tinker with.
| ethan_smith wrote:
| For optimal ADS-B reception, pair that RTL-SDR with a 1090MHz
| bandpass filter and place your antenna outdoors with clear sky
| view, as these signals are line-of-sight and easily attenuated
| by buildings.
| contingencies wrote:
| It is perhaps telling the author lives in the Netherlands! My
| findings were also that it's _really_ super important to have
| them up high... at which point you need decent cable,
| termination and general radio knowledge otherwise you are
| exposing yourself to other issues. Basically, if there 's
| complex topography, give up on this ever giving excellent
| results unless you have a radio tower or tree.
|
| The most common design for wire antennas at 1090 MHz is the
| quarter-wavelength monopole (such as a ground-plane or whip).
| For 1090 MHz, the quarter-wavelength in free space is
| approximately 68.8mm, but practical build recommendations
| round this to 65-66mm to account for the velocity factor of
| the conductor, especially if the antenna element is made from
| solid wire rather than thin tubing. For a dipole (the total
| length being half the wavelength), the length is
| approximately 137mm (ie. 2x68.5mm). Commercial antennas sold
| for 1090 MHz may appear longer because they are collinear or
| have internal elements designed for added gain or bandwidth.
| Catbert59 wrote:
| Also very interesting is the data which can be extracted from
| ADS-B.
|
| There have been several attempts from meterologists to extract
| wind data from through the actual and target direction values.
|
| Other sites use it to locate GPS-jammed areas because ADS-B can
| indicate when the reception fails (but still is able to transmit
| its position due to inertial fallback mechanisms).
| tjohns wrote:
| Related: Some airliners directly transmit automated weather
| reports via either AMDAR or AIREP.
|
| AMDAR: https://madis-data.ncep.noaa.gov/MadisAircraftPublic/
|
| AIREP: Go to
| https://www.1800wxbrief.com/Website/interactiveMap, turn on the
| "Pilot Reports" layer, and look for "ARP" symbols on the map.
| You'll mostly see these over oceanic routes, especially in the
| Atlantic.
|
| The AIREP reports are coded in PIREP format, so you'll need to
| look up the instructions for manually decoding those online.
| Catbert59 wrote:
| That was a huge drama during Covid-19 as weather forecasters
| heavily rely on these automated weather reports for feeding
| their models. In Europe there are also special equipped
| Airbus/Boeings for collecting WMO-grade weather data while
| flying their standard routes - they were mostly grounded
| during the pandemic.
|
| They partially replaced the data with the experimental Aeolus
| satellite which made its data into the productive forecasts
| within months due to their high quality.
| jasonjayr wrote:
| The weather model based on ADS-B data was [very recently]
| discussed here:
|
| https://news.ycombinator.com/item?id=44734515
|
| The article linked to this book, which is very comprehensive.
| zX41ZdbW wrote:
| I've decided to check if it's possible to generate temperature
| and wind maps in real-time.
|
| Temperature:
| https://adsb.exposed/?dataset=Planes&zoom=5&lat=45.8124&lng=...
|
| Wind direction (Europe mainly):
| https://adsb.exposed/?dataset=Planes&zoom=5&lat=46.8734&lng=...
| tiagod wrote:
| Section 1.2 reads:
|
| >The concept of PSR is fairly simple. It is a rotating radio
| transponder with an omnidirectional antenna.
|
| Shouldn't it be a directional antenna?
| CoolNamesAllTkn wrote:
| This book is a great reference! Junzi has it in website form as
| well: https://mode-s.org/1090mhz/ Much more affordable than
| purchasing a copy of DO-260.
|
| I consulted it a lot while working on an open-source ADS-B
| receiver project that decodes Mode S using RP2040 PIO.
| https://github.com/CoolNamesAllTaken/adsbee/
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(page generated 2025-08-06 23:00 UTC)