Jamming is easy though.

Just get a big transmitter, and transmit on the same frequency. If you overpower the signal on the reciever end enough that they can't make out a signal anymore, you've succesfully jammed it. You can fight that in a few ways, with a directional antenna, better signal processing to drown out the noise, better signal redudancy to make the processing easier, etc etc. In the end, it's just basics physics.

Of course, the downside of having a really big long range transmitter (like a jammer or rada) is that it's super easy to shoot a missile at it.