In a recent training exercise over Indonesia, two Russian made Su-30MK2 fighters were maneuvering near Sulawesi island when their radar warning indicators went off, indicating that a hostile aircraft was using its targeting radar on the Su-30s. One aircraft was operated by a Russian test pilot, the other by an Indonesian Air Force pilot. Both aircraft were immediately ordered back to base, since ground radar could not see any other fighter aircraft in the air over Sulawesi.
Indonesia had just received three Su-30MK2 aircraft, which are two seater aircraft, with the second crew member handling weapons systems and taking some of the workload off the pilot on long missions. Russian technicians were still in Indonesia, and they checked out the two aircraft. It was determined that some of the other electronics in the aircraft, used in a certain combination, were triggering the false radar warning.
This is an increasingly common problem. Last year, the U.S. Navy found its Silver Hawk UAVs are getting disabled by interference from other military electronics in Iraq. One of the more dramatic examples of this sort of thing occurred during the 1990 campaign to liberate Kuwait. There it was discovered that certain combinations of airborne jammer frequencies could trigger an involuntary launch of Patriot anti-aircraft missiles, as well as some less catastrophic, but equally unexpected events. Investigation of these incidents revealed something electronic warfare experts have been warning of for a long time. With so much exotic new gear, capable of putting out so many different signals, and in a huge number of combinations (which creates even more new electronic signals), there was no way to knowing what kind of impact this would have on existing military, and civilian, electronics. Throughout the 1990s, the problem only got worse. This became obvious as there were increased incidents of military electronics tests trashing, or playing with, nearby civilian electronic devices.
The military has been seeking solutions, because it's important for military equipment, especially communications and control systems, not to suffer electronic interference. In Iraq, is was quickly discovered that Warlock (a jammer that shut down enemy use of wireless signals to set off roadside bombs) also interfered with some military equipment, including some radios. This was not good. Such interference has occurred in the United States when this gear was turned on for training. There partial solutions to these problems, and that's the best anyone can provide so far.