The simplest (technologically speaking) GPS jammer could be any powerful transmitter in the 2.4GHz region. A slightly modified microwave oven would work perfectly. An unmodified microwave oven is already a significant source of interference to 2.4Ghz Bluetooth and WiFi communications while in use.
When handling jammer, is it troubled by no information? Whether it is because you do not know how much power left and do not know when to charge? It does not matter, there has been a display with a liquid crystal display jammers, the above will show the interference of the band, power and other information.
Whilst evading such jamming is easily possible and having an autopilot likewise, are they currently built into the available drones in a way that can not be overridden by a jamming system who’s manufacture has shall we say a not publicly known arrangement with the drone manufacturer?
This can be done with the kind of Wi-Fi RF cell phone jammer that is sold to military and government groups. These Wi-Fi jammers will stop most, if not all, hobbyist, commercial and unsophisticated terrorist drones and cause them to return to where they launched with very little chance of doing much more than interfering with people’s Wi-Fi connection in the very near vicinity.
Simply pushing lots of CW power into the ether is the most inefficient method of jamming and rarely used because of this. More efficient is a tailored jamming system that is modulated in a way that causes problems in the demodulator of the receiver being jammed, usually by using a high peek pulse power at a critical frequency to the receiver demodulation. Even more efficient is to mess with the stages beyond the receiver such as sending valid modulation that mucks up the computer data processing.