It is my understanding that all broadcast stations have been retro-fitted with a control box interface, hard wired to the regional EAS system, so the EAS has priority to override. Any attempt to remove or defeat the override renders the equipment non-functional. It is no longer in the station engineers control at all. Any group attempting to seize control and get a message out will have non-functioning equipment.
This has been done for several years now and has been posted on FR. When the time comes to keep Americans from communicating with each other, it can be done. Any radio transmissions from Amateur Radio Operators or CBers will be dealt with as needed. You can’t jam an entire continent - I think...
Correct; you can't jam the entire continent. It won't be easy to even jam one city. To be effective, every receiver in the city must hear the jammer many tens of dB above the signal of interest - on all frequencies, from HF to microwaves.
I don't see how the government could prevent ham radio operators from making contacts. Many RF links are local (especially on V/UHF) which means the government will not even know about those transmissions unless they are listening nearby. That's a lot of territory to cover - and don't forget that they must listen on all frequencies at the same time!
Just like it is with firearms, there are millions of HTs and base stations and repeaters in hands of ARRL members. Many hams have several rigs - one in the pocket, one in the car, one at home, one to take on a trip... All of them can be used to communicate. Unlike firearms, they operate quietly and don't require ammo.
The rules require every station to transmit its call sign every 10 minutes, or at the beginning and the end of each transmission. It's a gentleman's agreement. If the government decides to neglect its end of the deal - and especially if TSHTF - operators will be still using call signs, but they won't be issued by the government :-) And unlike firearms, there are no bullets or cartridges to inspect under the microscope to match the gun. On top of that, new radio equipment can be always manufactured; it won't be an FT-2000, but it will get the job done.
If the government hopes to detect unauthorized transmissions and triangulate the source, it is nearly impossible in cities and very hard to do in general. You'd need a very special setup, probably involving helicopters - and that depends on the theory that the transmitter is operating constantly. A guy working his mobile radio from a moving car can't be easily triangulated. Thousands of radio operators were active in World War II. They needed tens of minutes to transmit long messages in Morse code, and the opposite side was very willing to find them - and most commonly they failed to find them fast enough. Today the message can be much shorter due to computer-based modulation schemes. PSK31 and RTTY are faster than the best CW operator in the world, and they don't require much of a training to use.