alt Hacker NewsBecause GPS and other GNSS have only a very weak signal strength there are no jam resistant frequencies, you can jam them all very efficiently, or you can jam them very efficiently in selective way (jam BeiDou, but not GPS).
GPS was jammed even as early as Iraq war.
"Coalition troops also got a glimpse of GPS’s greatest weakness during the Gulf War. Iraqi forces installed jammers, for example, on top of landmarks such as Saddam Hussein’s palaces to prevent them from being hit, Mastalir says. This helped the military realize early on that it would have to further develop its laser-guided munitions and other weapons that acquire targets when GPS is unavailable"
https://web.archive.org/web/20160208233555/http://www.scient...
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A lot of work is being done to make GPS more jam resistant, and - just as important - more spoof resistant. The latest batch of satellites has a whole raft of countermeasures to help a receiver to identify whether the received signal is genuine or whether it was spoofed. Receivers too can do a lot to detect spoofing by just observing the signal (for instance: unrealistic power levels on reception, impossible response to vehicle movement and others besides), but quite a few of those are unrealistic or too expensive for regular (non military) applications. Jam resistant frequencies do not exist as you already mentioned, from a physics perspective. But GP might mean this to refer to the new M-Code signal, and these are sent out on different frequency offsets from the main carrier, so effectively different frequencies.
I think Starshield (Starlink for the military) is going to use lasers as the means of communication (and location). Those are highly directionaly, and likely not possible to jam. Though I'm not sure how resistant are they to atmospheric interference, and the sats need to know where your receivers are, which I can't imagine the military is too happy about.