After watching CSI:Miami a boater was told “you get a pass on your illegal GPS unit.”
How can a GPS receiver be illegal?
I don’t think it can.
A few years ago, GPS satellites operated in ‘Selective Availability’ mode. That mean that civilian GPS receivers were much less accurate than the ones available to the U.S. military. So I suppose in that situation a GPS unit that had SA turned off might have been illegal.
SA has been turned off for a long time now, so there’s no functional difference between civilian and military GPS units.
Another possibility is that marine GPS units have to be specially certified to be installed on the boat. I’m not a boater, so I don’t know if that’s the case. Certainly if you want to install a GPS in an aircraft it must be specially certified. So permanently installing a GPS not rated for aircraft use into the panel would make it ‘an illegal GPS unit’.
Umm…
close, no cigar.
A non-certified unit can be installed in an a/c (a common practice in homebuilt circles) - but the a/c cannot be certified for IFR operations based on the presence of the unit.
Additionally, it would be possible for a FAA inspector to declare the presence to be an unacceptable distraction and actually revoke the airworthiness certificate of the a/c, but such draconian actions are rare.
For maritime uses: WAG - many units feature moving maps (show the unit’s position and movement relative to geographical features) - if the map is out of date, it would not be legal for navigation - this would be a problem if the vessel were used in such a manner as to require that in info be accurate, but, if the boat is a pleasure craft never operated out of sight of land, the GPS would simply be a toy - not required, therefore not of interest.
There are several reasons why the military band still exists, is encrypted, and why US military might not want the general public able to use it. (You’re right about selective availability being off at the moment)
The military band is presumably fairly equivalent to the civilian band; yet during the days of selective availability the US military was known to have the formula for the pseudo-random variation that limited the accuracy of the civilan GPS units, so that they could use it as civilians use it now. There’s a reason for this- the two bands are at different wavelengths. Using two different wavelengths at the same time enables a number of error corrections unavailable to those with only one wavelength (diffraction based errors can be compensated for by extrapolating from the difference in the signals, for example)
The second reason is that under certain circumstances the US military might decide to eliminate or modify the civilian-(and therefore enemy-)available GPS signals, to thwart enemy use of GPS in a combat action. In this case it would be very useful for the US to have exclusive access to an accurate set of GPS signals on the military band.
On the other hand, I doubt people are commonly installing military GPS- I suspect happyheathen’s reasons are more commonly found. (Though it would be concievable for just the right sort of hacker to do it to get the increased accuracy)
HappyHeathen: Not quite. I specifically mentioned PERMANENTLY mounting it in the aircraft. In which case, the installation has to be STC’d. The same would apply if you wanted to install a tape deck.
If you want to fly IFR with your GPS, it has to be TSO’d and approved for IFR flight.
Homebuilts are a whole 'nuther matter. No STC required, but you still require the TSO and certification for IFR flight.
HappyHeathen: Not quite. I specifically mentioned PERMANENTLY mounting it in the aircraft. In which case, the installation has to be STC’d. The same would apply if you wanted to install a tape deck.
If you want to fly IFR with your GPS, it has to be TSO’d and approved for IFR flight.
Homebuilts are a whole 'nuther matter. No STC required, but you still require the TSO and certification for IFR flight.
Not quite true. The civilan signal is used to locate the military signal. Jamming civilian signals will cause the military signal to be jammed too (here ).
Listen to it here
The military wouldn’t be “jamming” the civilian signal; they would just reintroduce SA.