Mode-S Receiver

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Revision as of 17:57, 5 July 2011 by Mid (Talk | contribs)

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WTF is Mode-S?

Mode-S is the radio protocol used for secondary surveillance radar in the United States and most of the world. It is a direct descendent of Mode-A/C, which were originally used to add simple supplemental data to the primary radar returns on air traffic controllers' displays (like altitude and assigned squawk code). It is not literally RADAR, but it is a data protocol on a separate frequency (1090MHz), with by equipment generally co-located with primary surveillance radar systems (often 1030MHz). In Europe now and the US eventually, a new higher-level protocol, ADS-B, is being implemented on-top of Mode-S. ADS-B allows for more sophisticated two-way data transfer data between ground stations and equipped aircraft. Right now in the US, most aircraft only transmit Mode-S, but any flight going to Europe generally supports ADS-B. Most importantly, ADS-B-equipped aircraft generally transmit their location, so that aircraft can be tracked by anyone within line of sight, instead of relying on primary radar returns. (The US is eager to move to ADS-B, as it means they can get rid of those hundreds (thousands?) of secondary surveillance radar stations they have to maintain across the US territories, and replace them with very simple systems not dissimilar to that described here! Also note that the US will also support ADS-B implementation via the UMT datalink instead of "1090ES"; this is a different thing and isn't covered by this project.)

What's at 2169

mid and Balint installed an antenna tuned for 1090MHz on the noisebridge antenna masts. It runs to bunny, a Geode LX800 motherboard with a microADS-B PIC decoder inside a NMEA/IP-67-rated weatherproof can powered over fake-PoE. It's running Voyage Linux, why not. In testing, it has been able to follow aircraft over 150 miles away (we picked up the Aeroflot A330 from LAX to Moscow on the other side of the Sierra last weekend, as well as flights en route over Paso Robles).

Currently it is not operational due to interference issues between the motherboard and the PIC (and perhaps a host of other problems). mid, jbm, and Balint have a plan! It likely involves aluminium foil and gobs more electrical tape. Also the mounting+cabling is a crime against engineering—we'll fix it ASAP.

Long-term plan

  • Provide a freely-usable timestamped stream of data in the "port 30030" protocol used by most of the rest of the ADS-B hobbyist community
  • Contribute the stream to the community to increase coverage of the bay area
  • Put up a fun slippy map display
  • Pool data with other bay area hobbyists to try to do real-time multilateration on aircraft that only transmit non-positional Mode-S data


  • mid started this and donated a bunch of hardware
  • jbm has been helping make bunny work
  • Balint has been contributing motivation and has vast radio knowledge whenever he's in town
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