I think that whilst GPS is an excellent tool, it should be remembered that it can be switched off at any point by the authorities. In the early days of GPS two standards existed, civilian and military. The civilian signal was degraded with an error which would be up to 100m, and the error changed every hour. Today we see accuracies of 300mm possible from civilian units.
I can totally understand the reason and need for a jamming unit, all that would do is disrupt the signal from the GPS satellite to the GPS unit making the GPS unusable in the area covered by the jamming transmitter. It’s not rocket science, any radio ham could potentially make one. It would not be legal, but technically not difficult.
The need for a jammer? That’s easy, if we do a Google search for UAV autopilot then it’s easy to find both ready made GPS guided autopilots units for UAV’s (which in their simplest form are model aeroplanes) and build your own unit designs. Now imagine the scenario, somewhere sensitive, or a sensitive event, someone has one of these units (GPS guided device) and its used to position a model aeroplane loaded with something nasty to within a meter of where the person wants it to go.... It becomes a very easily available guided weapon.
I think we have to accept that we live in a very unstable world, that we have no right to GPS services (in fact the use of it should be looked on as a privilege rather than a right) and that the use of it can be removed without notice. WE all need to go back to basics, and remember that GPS can fail, get jammed or be switched off without notice.