It's been claimed by various observers that Russia is behind GPS glitches in Romania and Bulgaria.
The next day, September 1, it was happening again. Pilots approaching Sofia complained of the same problem, according to transcripts seen by RFE/RL's Bulgarian Service of recordings from a Sofia Airport radio channel. The plane spotter's findings were also confirmed by GPSJAM, a website documenting jamming activity.
The jamming had also happened before. Romania experienced a similar problem with its GPS system, a glitch that the army's chief of staff blamed on Russia and said posed a significant risk to shipping in the region. While Bulgarian officials are being careful not to directly accuse Russia, they have said that the problems with GPS largely date from the start of the Kremlin's full-scale invasion of Ukraine in February 2022.
Asked by RFE/RL who was behind the jamming and how Sofia is countering it, the Bulgarian Defense Ministry was circumspect, only saying that the jamming was being carried out "with radio-electronic warfare systems." [...]
The Royal United Services Institute's Withington says he believes that much of the jamming is done by equipment deployed on Russian warships in both the Mediterranean Sea and the Black Sea.
Is it technically feasible for Russia to jam GPS signals that far from their shores, i.e. well inside Bulgarian territory (see where Sofia is on a map—like 400 miles from the Black Sea shore and 200+ from the Aegean) using ships in the Black Sea and the Mediterranean? And have such jamming ships actually been spotted there doing such? Because I imagine they'd have to put out a pretty strong signal that would be easy to triangulate back to the source.
For instance Jane's says: "The truck-based R-330Zh Zhitel system was then used to interfere with satellite communications equipment, as well as navigation systems and mobile phones within a 30 km radius." But that's far below what's been implied for those alleged ship-based capabilities.