HP 29 GPS: the view from 9865 meters!

[Paul Dale]

(06-02-2017 06:01 AM)PANAMATIK Wrote:  That's interesting. I knew only of the software imposed position inaccuracy, which is deactivated for civilian areas today, but of course from military view height and speed would be important informations for enemy missiles.

This would be Selective Availability. This used to be enabled and it intentionally degraded the GPS position for civilian use. It was turned off about 2000 and I don't think it has been turned on again.

For military use, there is an extra signal broadcast which supposedly provides ten times the accuracy. This signal is encrypted, so most GPS receivers can't decode it. The carrier wave from this signal can be used to improve the fix on a civilian GPS by some clever trickery.

There have been localised GPS black outs since selective availability was turned off. The war in Georgia against Russia is an example. This prompted the Russians to update and complete their GLONASS constellation. Good receivers will use both GPS and GLONASS signals (& the European Galileo ones).

Quote:I don't know what happens in the HP-29E GPS when more than 1000 knots are displayed (see picture no digit left), Geoff, please keep below this barrier.

Geoff's planes don't go anything like that fast. 1000 knots is well into the supersonic range.


Pauli