A jammer for a specific service like signal jammer can simply be a low power transmitter on the frequency range used by the GPS satellites. Even if it transmits enough signal to overwhelm your GPS receiver for a few feet, anyone standing near you could carry one in a pocket.
Billed as the only operational tactical jamming fighter in the world, the Growler is a specialised version of the F/A18-F Super Hornet, and since achieving initial operational capability in September 2009, it has been equipped with the AN/ALQ-99 airborne EW system. The AN/ALQ-99 itself, however, can claim much older ancestry, having been designed in the late 1960s, and first fielded in 1971with the introduction of the EA-6 Prowler, the EW variant of the A-6 Intruder, in time to see combat service in Vietnam.
The concern comes as civilian aviation and communications systems have repeatedly been jammed in connection with nearby Russian military activities.The situation was similarly serious in September 2017, when airliners from companies SAS and Widerøe in periods had to navigate with the help of radio signals due to loss of GPS when they entered the East Finnmark airspace. The jamming coincided with the major Russian military exercise «Zapad».
Jammers work on the principal of interference. It is similar to you trying to have a conversation with your friend in an airport runway, where a jet engine is turned on. You wont be able to listen to any thing because of the jet engine. A signal jammer works like a jet engine in this case, instead of noise it generates radio waves of all frequency’s simultaneously and does not let your device connect to the network.
If China is jamming US Navy aircraft flying in international airspace at sea, it serve as yet another sign that Beijing may disregard international law and norms to defend its South China Sea land grab.Never-the-less, straight-forward jamming is unlikely to pose the greatest threat, primarily because it is a very blunt instrument and not one that is likely to pass unnoticed. In the event of any abrupt loss or sudden degradation of the signal, a surprising range of devices will detect the problem, not just the GPS receivers themselves, and sound the alarm.