GPS has a type of frequency hopping. Rather than jumping around from frequency to frequency, it slides up and down the spectrum like if you were turning an anal

GPS has a type of frequency hopping. Rather than jumping around from frequency to frequency, it slides up and down the spectrum like if you were turning an analog knob. The movements are determined by a pseudo random number generator unique to each satellite. Civilian GPS receivers have these PRNG keys so they can follow the movements up and down and stay locked on to the carrier while filtering any potential interference or jamming. For military use they have a second PRNG that lines up with the civilian PRNG once every 10 cycles. So between every ping your phone or car GPS gets, there are 9 more military only ones that move around the spectrum randomly and have some other security features. To jam GPS you either need the PRNG keys to know when to move your jamming, or just blanket the entire spectrum with random noise. If you take the blanket everything approach receivers may still be able to pick out the carrier (because it is moving and a detectable change). (This isn't actually how it works, but is a simplified example of the concept. GPS is an amazing protocol that I don't even understand most of. There is some really cool stuff like using two different frequencies to measure the delay introduced by the ionosphere. The Coast Guard manages a lot of the civilian side of things and has plenty of rabbit holes you can go down: https://www.navcen.uscg.gov/?pageName=GPSmain https://www.navcen.uscg.gov/?pageName=GPSmain)