A couple of years ago, flying from KFFZ in Arizona, my Bendix-King KLN89B starts acting up, map page all skewed, inop time/distance data, so I tell the tower.
They make a telephone call.
Yup, it's TRW again, with their test signals.
The FBI is called.
Their chief engineer on site is propmptly arrested and read his Miranda rights.
No problems since.
Nobody f***s with my GPS signal.
Period.
If they try, I know just whom to call.
A completely true story.
The FBI takes unwarranted GPS interferrance very seriously in the USA...jail time for the perps, make no mistake.