Comment by jevinskie | Hacker News Reader

Comment by jevinskie | Hacker News Reader

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Unfortunately many receivers have a (speed > X || altitude > Y) check when, IIRC, the law only requires (I don't see the altitude part in your quote) (speed > X && altitude > Y). I think the altitude limit was 20 km or 25 km. Anyways, it is a pain for people who want to put a receiver on a high altitude balloon. I was able to... find... a modified firmware for my SIRF receiver but I have been to afraid to flash it. Besides, I don't even know if the receiver has the "bad" logic. I've been jonesing to make a SDR GPS simulator that generates a signal that I can feed directly into the antenna port on the receiver to test high altitude functionality.

MTCR is an informal agreement, not a treaty. Its provisions are actually implemented by laws in the member nations-- in the US, that's the International Traffic In Arms Regulations Act. (ITAR) ITAR Category XV, Section c:

  Global Positioning System (GPS) receiving equipment specifically 
  designed, modified or configured for military use; or GPS receiving 
  equipment with any of the following characteristics:
    1. Designed for encryption or decryption (e.g., Y-Code) of GPS 
       precise positioning service (PPS) signals;
    2. Designed for producing navigation results above 60,000 feet 
       altitude and at 1,000 knots velocity or greater;

So the US limit isn't even in metric units! Consulting my psychic powers, since I haven't bothered to dig up the laws for each member nation, I predict that each nation implements MTCR slightly differently, some using the word AND, some using the word OR. Since a GPS manufacturer wants to sell worldwide, they would have to use the strictest limits possible.

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