Mode S Technology





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Interview with Paul Drouilhet, 10/29/00

  • The "biggest effect that [GPS Squitter] will have is the ability for aircraft to know where they are, who's around them, and who's out there...." Right now aircraft are "totally dependent on ground stations to keep them separately." It "opens up a whole new way of possibilities" for managing aircraft in the sky.

  • There are other Europeans experimenting with ADS-B, but using three different alternatives: GPS, UAT (Universal Access Transponder), and VDL Mode (Very High Data Link, developed by the Swedish). GPS and UAT use frequencies above 1000 MHz, but VDL uses the VHF frequency bands.

  • In DABS, selective interrogations can be used (hence the term Mode S). Each aircraft has a unique address and broadcasts it every so often, sort of "like a flashing light....every once in a while, it sends out saying I am here, here is my address code. "If another aircraft hears that, then it will send that interrogation with that address."

  • The GPS squitter "is an expansion of the signal." "What has changed is that GPS Squitter "adds to the broadcast, GPS info...the previous Mode S squitter [just] broadcasts altitude." "The GPS Squitter has taken [Mode S], added more bits and in those bits, transmit information as derived from GPS."

  • "It's a complicated question where [the original idea] can be see in the cartoons as suddenly the light goes off." "There was a lot going on in ways to improve aircraft safety, so I can't honestly say..." "I was very involved with Mode S...and quite familiar with Mode S, so I was the first to say that we have a signal that is ready-made but when and where it was invented is a mystery."

  • The Story of Mode S: An Air Traffic Control Data Link Technology last modified: 12.06.2000