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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.

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  • Why do you think the jamming originates from land and not from aircraft?
    – Weather Vane
    Oct 28 at 17:47
  • @WeatherVane: for all I know they could be using satellites to do this. I just want to understand how this is claimed feasible from a technical perspective when it's a bit unintuitive given the distances involved.
    – Fizz
    Oct 28 at 19:35
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    They have been described as spoofing GPS before, though not this range.
    – User65535
    Oct 28 at 21:28

3 Answers 3

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tl; dr: GPS jammers can be small and portable devices. If Russia is jamming GPS reception outside their territory, it may very well be done by agents present in the area. A GPS jammer is by no means hi-tech equipment, but just a simple noise transmitter.

GPS jamming is technically not difficult and can even be done unintentionally. If you tune an FM radio to 94.3 MHz, the 15th harmonic of the mixing oscillator overlaps with the GPS L1 signal, which can cause drop-outs in GPS reception in the surrounding area. The oldest story about GPS jamming I could find is from the 1991 Kuwait war, where Iraqi forces allegedly used GPS jammers to prevent GPS guided US missiles to reach their intended targets, so GPS jammers have been used in warfare longer than one might think. It is also just a specialized case of radio and radar jamming, which have been used at least back in the second world war.

Instructions for building GPS jammers are publically available. Even with minor knowledge in electronics, you can modify the circuit to transmit at a higher power and hence jam the GPS signal over a larger area.

With the establishment of additional navigation systems (Galileo, GLONASS, BeiDou) over the last years, most receivers do not solely rely on GPS reception, but are also able to simultaneously use the other systems as well, primarly to increase accuracy. If only GPS receptions is jammed, such receivers can usually still get a navigation fix by using signals from other systems. It is however just as simple to jam the other navigation systems as well, so it is not unlikely that multi-system jammers are being used.

Since spoofing was mentioned in a comment, I would just point out that jamming and spoofing are two different concepts. While a jammer only prevents the receiver from determining its position, a successful spoofing attack will trick the receiver into believing that it is somewhere else. That is a very much larger cup of tea and difficult to accomplish, but there is nothing in the linked article indicating that Russia is spoofing GPS reception outside their territory.

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  • This answer seems to be premised on the concept that "If Russia was deliberately targetting one city in Bulgaria, they could do it." I am no expert on the geopolitical situation in Bulgaria, but is there any reason to believe that Russia would want to target Sofia (as opposed to the blanketing Ukraine from the Black Sea and not caring much if the east coast of Bulgaria suffers (which the jamming map shared by the original claimant might suggest.)
    – Oddthinking ♦
    Oct 30 at 16:57
  • @Oddthinking I was answering the question: 'Can Russia ...', 'Is it feasible for Russia ...'. The answer is: Yes, they can.
    – Tor-Einar Jarnbjo
    Oct 31 at 11:29
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Height of Eye

It's worth noting that airline pilots are complaining of jamming. Jamming is going to be (close to) a line of sight operation. That means things like trees, buildings, the curvature of the Earth, etc. will all block or scatter a jamming signal.

The 30km range quoted in Jane's is almost certainly for a ground based jammer interfering with a ground based GPS receiver. But a airplane coming into an airport will have a clear line of sight on the jammer from a much longer distance.

Indeed, the same Jane's article you link to states (emphasis mine):

Krasukha-2 is intended to jam airborne warning and control systems (AWACSs) at ranges of up to 250 km

Further, an airplane might have direct line of sight on multiple jammers, so even if each individual signal is weak, the noise is additive.

I'd expect that as the airplane descends for landing it's GPS reception would improve as the height of eye decreases and fewer jammers are visible.

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  • It is not entirely unlikely that if the reports from Sofia all come from airplanes, which are ascending or descending from the airport there, that the cause is unintended stray noise from a jammer located in the Black Sea. But if that was the case, it sounds unlikely to me that airplanes going to and from the airport in Plovdid do not experience the same problem.
    – Tor-Einar Jarnbjo
    Nov 1 at 14:45
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There are long range jamming systems, as @Tor-Einar Jarnbjo said jamming is relatively easy and mainly involves high power, simple and "dumb" transmitters

Some examples:

100km

200km

250km

560km

and even 1000km

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  • Is it reasonable to think that this would give a jamming map like the original claimant shared, with areas between the Black Sea and Sofia relatively clear of jamming? [I looked a relief map of Bulgaria and thought "Ohh, maybe the mountains around Sofia are high enough to get signals from the Black Sea where intervening country isn't" but then realised these readings are coming from planes, and mountains might not be a factor, so I should remain open.]
    – Oddthinking ♦
    Oct 30 at 17:01

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