Honest question, I assume playing with this is completely illegal in the US??
I guess you can get in real trouble if you are catched faking GPS signals? Does anyone know what are the regulations for something like this?
The FCC rules for Amateur radio which is defined in Part 97 clearly states that an amateur may not disrupt radio location services. The frequency for the GPS Signals, high UHF is not close to any privileges available, amateur operators included. In short, don't do this unless you're testing / putting out very low power. Better yet, get an RF enclosure.
The FCC would have absolutely no problem at all throwing around at least 5-digit fines for doing these things.
Beyond that, though, GPS is still considered military technology. The state department could very well come after you for exporting military tech were you to even make a blog post about it while based-in or having any ties to the US. They really don't fuck around with this stuff.
I got to play with a real GPS simulator a few years back for a school project (visiting the local defense contractor to verify some equipment) the narrow part of which was testing an unlocked (height and velocity restrictions disabled) GPS receiver as it would work in LEO.
You can get a Part 5 experimental license, although a likely condition of getting such a license would be taking steps to ensure that your work doesn't interfere with devices outside of a small designated test area. Alternatively, you can do all the GPS experimentation you want inside of a shielded chamber without asking permission from anyone.
Yes, very illegal. Which makes me remember to ask: how did Todd Humphreys get permission to transmit a spoofed signal [1] in the middle of a thriving metropolis, within a couple of miles of an airport?
Here is a graphic of the spectrum available in the US: https://www.ntia.doc.gov/files/ntia/publications/2003-alloch...