I heard that they were waiting for the patent holder's patent to expire, but just wanted to confirm.

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    $\begingroup$ Mode-S transponders with extended squitters (ADS-B) send this information, and is part of the Nexgen update. $\endgroup$
    – Ron Beyer
    Jul 6, 2017 at 4:33
  • $\begingroup$ \what patent and who is the holder? GPS is only useful to increase accuracy. Standard secondary RADAR knows the aircraft position already. Are you asking about ADS-B or something else? What do you consider to be other important info? $\endgroup$
    – Simon
    Jul 6, 2017 at 4:43
  • $\begingroup$ Because many if not most transponders pre-date GPS? $\endgroup$
    – jamesqf
    Jul 6, 2017 at 5:19
  • $\begingroup$ @Simon I believe its this one google.com/patents/US5289183 . Originally intended for motor vehicle traffic network, it has broad claims that would include said technology. Google, Honeywell, Uber, Lyft, and many other companies were waiting for this and other patents to expire to totally revamp transportation networks while avoiding licensing fees. Since this one was filed in 1992, it has already expired but I think there is another one they are waiting expiration on. What other important data? too numerous to list here. $\endgroup$ Jul 6, 2017 at 11:29
  • $\begingroup$ Related $\endgroup$
    – Pondlife
    Jul 6, 2017 at 12:01

1 Answer 1


Basic transponder technology is old, predating GPS. Basic transponder operation (also called Mode A) only sends the programmed code, which can easily be represented as four octal digits. (In fact, before that, only two octal digits worth of data were programmed and sent.)

Later, a representation of the aircraft's (transponder's) altitude was encoded and sent along with the programmed code. This is Mode C.

As noted in the comments by Ron Beyer, the new transponder standard (the ADS-B Out technology) can send the GPS location information.

See also Why is the range of transponder digits 0 to 7 rather than 0 to 9?.


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