(The title is actually "The 1090 Megahertz Riddle".)
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.
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.
Plus
https://de.aliexpress.com/item/1005009237905498.html
Maybe you can find an antenna with both integrated.
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.
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.
Well, 1090 Mhz is a crap frequency to run through coax cable for long distances. The attenuation is pretty high at that frequency already. So I wouldn't just mount the antenna on the roof and then coax the RF down a few floors. You will reduce your range.
I would simply mount the SDR itself right up on top of the mast, along with a raspberry pi to decode everything. Then add a PoE HAT and all you need to bring down is Ethernet for which long distances are no issue. The PoE uses 48V so it also bypasses the problem of voltage drop on 5V with high current. Put it all in a waterproof box of course. Ideally metal for heat dissipation because waterproof means no airflow from outside to inside.
Make sure you use real copper Ethernet cable and not that CCA crap (copper clad aluminium) because that has much higher resistance and does have big problems with PoE. All the cheap cables are CCA these days so beware.
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).
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.
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.
https://news.ycombinator.com/item?id=44734515
The article linked to this book, which is very comprehensive.
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=...
>The concept of PSR is fairly simple. It is a rotating radio transponder with an omnidirectional antenna.
Shouldn't it be a directional antenna?
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/
Ps Elon is not against ADS-B but against people sharing the received data and scrutinising his private jet use. Not sure why that would be a deterrent to do that though.
toomuchtodo•6mo ago
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•6mo ago
I'd take issue with the phrasing "moved from" and would rather use "supplemented by". Controller-based interrogation is still widely used.
touisteur•6mo ago
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.
ptero•6mo ago
On the defense side ADS-B can provide a baseline air picture of cooperative traffic, but does not otherwise help with detecting non-cooperative aircraft.