Block a drone with a mobile jammer? Good luck with that…

The EFF getting forcibly removed from parliament and the scuffles that ensued might have been the highlights of President Jacob Zuma’s State of the Nation (SONA) address, but as has now been well documented one of the most concerning activities of the evening was the fact that a cell phone jammer was deployed inside the Parliament buildings, causing great consternation from journalists trying to report on what was going on.

Yesterday, State Security Minister David Mahlobo said that it the jammer was deliberately activated in order to create a “no-fly zone”, but should have been switched off.

Quite what Mahlobo was afraid of flying through parliament is unclear, but he was referring to unmanned aerial vehicles (UAVs or drones), the question is how effective is a mobile phone jammer against them?

So what exactly is a mobile phone jammer, and how does it work?

This is how it works

The technology employ to block or jam mobile phone signals is actually a very simple process. It’s so simple in fact, that you will be able to find blueprints on the internet on how to build your with just a television remote.

But with that said, it is also hugely illegal for anyone without the proper clearance to deploy (or even possess) one. In South Africa, only security services (including the police) are allowed to use them.

A mobile phone jammer is essentially a denial-of-service attack, which floods targetted areas of the radio spectrum with a blast of very loud white noise. This interferes with the mobile phone’s ability to contact the cell tower, thus causing it to loose functionality.

It’s like standing next to someone with a megaphone, shouting into their ears – they won’t be able to hear anything else except the shouting.

The brilliant website How Stuff Works describes it rather well: “Jamming devices overpower the cell phone by transmitting a signal on the same frequency and at a high enough power that the two signals collide and cancel each other out. Cell phones are designed to add power if they experience low-level interference, so the jammer must recognize and match the power increase from the phone.”

Jammers can interfere with 3G, 4G, CDMA, GSM and GPS signals, but it’s usually the military-style jammers that can cover the entire gamut of connectivity.

But since they block out mobile phone signals, can it be used to jam the signals of a drone, or Unmanned Aerial Vehicle (UAV)?

Journalists inside Parliament during SONA circulated pictures of a device they suspected to be the jammer. This is it.

It appears to be high power, military spec machine – a little like this. Generally speaking, most of the commercially available designs are built to block signals ranging from around 400Hz to 2.4GHz, which is where almost all mobile phone traffic takes place.

Can it block a UAV?

Well, according to House4Hack’s Schalk Heunis – who designs, builds and sells quadcopters – trying to prevent a drone from flying anywhere near the Parliament building is going to be a bit of a struggle.

Actually, it is going to be near impossible.

“It is possible to block the signals of cheap drones that you can buy at a toy store, but serious drones are a different story. The majority of them use a different frequency to what the purported device (and any other mobile phone jammer) use.”

The popular DJI Phantom, for example, is designed to be flown with a 2.4GHz or 5.8GHz signal for the controller.

Even in the event that it was theoretically possible to fill the spectrum with white noise used by drones, modern radios on UAVs can signal-hop – a technique deployed by operators to switch to a different, clean frequency band when interrupted.

Heunis also explained that while multiple control channels are possible, at the end of the day it really depends on what you want to do with the drone.

“These drones can do autonomous flight, and will keep on flying even if there is a jammer activated in the area.”

“It’s almost impossible to block a drone with a signal jammer. Maybe a regular drone, but not the serious ones. The sophisticated stuff is difficult to block.”

But that is not to say that the device wasn’t military grade, but if that was the jammer in question (and Mahlobo suggested there was more than one) then its range would likely have been very limited. It appears to have had its antennae removed.

What was it used for?

We’re still waiting for further clarification as to what the jamming device was actual in place for, but many in the security cluster has speculated that jamming device was switched on the prevent remote detonations of explosives while the president was making his way into Parliament.

This is a theory to which Gerrit Maritz, an electronics expert, subscribes. Maritz is sceptical that the jammer’s sole purpose was to block drones overhead.

“I would propose another theory that UAV’s might not have been the only true target behind the jamming and that it was indeed to jam mobile phones, albeit temporarily,” Maritz told us, “The negligence to leave it switched on might very well be the truth. The commercial jammers are mostly advertised as a countermeasure to remotely detonated bombs and improvised explosive devices (IEDs). If this was the original intention then it makes sense that they jammed the mobile frequencies while the president was outside and intended to switch it off immediately after.”

Either way, an investigation has been launched and complaints have been filed with the related agencies, and until then, nobody can be certain as to the device’s intention.

“The unknown nature of the threat that they were aware of makes it very difficult to guess as to what the intention was behind the jamming,” Maritz concludes.

We get a feeling that this won’t be the last time that we’ll hear about mobile phone jamming when it comes to South African politics.

Mahlobo on Wednesday said, “this isn’t the first time it was used, and it won’t be the last time.”


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