A Teardown Of Something You Should Not Own

GPS jammers are easily available on the Internet. No, we’re not linking to them. Nevertheless, GPS jammers are frequently used by truck drivers and other people with a company car that don’t want their employer tracking their every movement. Do these devices work? Are they worth the $25 it costs to buy one? That’s what [phasenoise] wanted to find out.

These tiny little self-contained boxes spew RF at around 1575.42 MHz, the same frequency used by GPS satellites in high Earth orbit. Those signals coming from GPS satellites are very, very weak, and it’s relatively easy to overpower them with noise. That’s pretty much the block diagram for these cheap GPS jammers — put some noise on the right frequency, and your phone or your boss’s GPS tracker simply won’t function. Note that this is a very low-tech attack; far more sophisticated GPS jamming and spoofing techniques can theoretically land a drone safely.

[phasenoise]’s teardown of the GPS jammer he found on unmentionable websites shows the device is incredibly simple. There are a few 555s in there creating low-frequency noise. This feeds a VCO with a range of between 1466-1590 MHz. The output of the VCO is then sent to a big ‘ol RF transistor for amplification and out through a quarter wave antenna. It may be RF wizardry, but this is a very simple circuit.

The output of this circuit was measured, and to the surprise of many, there were no spurious emissions or harmonics — this jammer will not disable your cellphone or your WiFi, only your GPS. The range of this device is estimated at 15-30 meters in the open, which is good enough if you’re a trucker. In the canyons of skyscrapers, this range could extend to hundreds of meters.

It should be said again that you should not buy or use a GPS jammer. Just don’t do it. If you need to build one, though, they’re pretty easy to design as [phasenoise]’s teardown demonstrates.

67 thoughts on “A Teardown Of Something You Should Not Own

  1. Given the power levels of things like this jammer are way more than the signal levels that a GPS receiver would ever expect, I’m surprised that they (the devices) couldn’t ‘self-diagnose’ that they were being jammed.
    Okay, they can’t do anything about it but at least logging it (plus, where it last known location and how long it lasted for) could highlight anything suspicious/nefarious going on.

  2. Considering the GPS signals are so weak would it not be possible to passively block them with something like a little Faraday Cage? That way you are not disrupting any near by GPS devices that are not your intended target.

    On the more advance GPS spoofing attacks, a team of students a few years ago demonstrated that you can make a ship think it’s in a completely different position to where it actually is with out raising any alarms on the bridge. In this case it was a luxury yacht and just a demonstration but the potential of such an attack method is quite scary. For example you could spoof an oil tanker to thinking it was 50km away from a dangerous reef when actually its been steered directly on to it and if you are a pirate with the right resources you could steer a ship towards an ambush.

    Doing a little research before posting this it would seem someone is already testing a system in the Black Sea:

    Story about students hacking Ship GPS:

    1. If you think this is scary, you probably should know that ADS-B, which is used as “secondary radar” for civil air traffic is completely open to spoofing and has no verification whatsoever on who’s actually transmitting what information…

      Furthermore, Airbus and Eurocopter have the collision detection systems connected with ADS-B and if on autopilot and with no pilot action despite the alarms, it will actually change course in order to avoid collision. Needless to say that high rise buildings do not have collision avoidance systems, so it probably is possible to steer a jetliner into one without being on the plane or doing any modifications to it.

  3. If GPS satnavs weren’t avilable it would certainly improve driving standards.
    People might plan ahead and read the 50ft tall junction signs than rely on a little box and swerve across traffic at the last possible moment without thought for anyone behind them.

    If people cannot function at all without technology to do it for them, more fool them.

        1. I guess it’s a little bit of A and a little bit of B. Cars are also a lot easier to drive, roads are built with some safety standards, people are better drivers due to the fact that cars are an everyday thing now and yes, cars are not death traps anymore.

        2. Seatbelts. Airbags. Deforming bodyshells. ABS. and so on…

          It’s commonly found that devices in the car distracting people from the road are a major cause of accidents.
          That has gone up with time and gadgets massively.
          Fines and loss of license from using portable devices is rocketing in the UK.

          Ever seen someone on their mobile phone in traffic using the car’s collision avoidance features to keep crawling along while they text? Look for it. It’s happening more and more.

          Google, Apple et al are making facial recognition for the front camera, why the hell are they not stopping them from working when people are driving and holding/looking at them?
          It wouldn’t be hard.
          Front cam sees face looking up and down constantly with a pattern akin to driving distracted.
          Back cam sees steering wheel, car cockpit.
          GPS sees movement and location.
          Put it all together. Lock phone for 10mins as punishment except emergency calls.
          Keep upping the time if it happens again.
          People would get the lesson fast.

          Change the law so the makers are legally responsible for the use and can be sued for injuries by 3rd parties.
          Watch it get implemented in days.

          1. The real reason – perpetual traffic jams forcing cars to drive slower. Seriously. The number of cars on the roads have increased faster in the last 40 years than the number of highway lanes to drive on. Traffic speeds in most NA cities are slower than back then as a result. Slower traffic = fewer accidents and less severe accidents. Weekend driving, with fewer traffic tie-ups, results in more accidents and higher death/injury rates. Forget the ABS/airbags/etc. Speed kills now and in the past. We are experiencing lower speeds on the average (over 25 year period ending about a decade ago, L.A. saw a 30% drop in rush hour speed).

          2. Since most phones have GPS, and all can be triangulated from base stations, it wouldn’t be hard for a phone’s OS to disable it, if it detected it was moving above, say, 5mph. You could probably do 5mph on foot but it wouldn’t be safe to use your phone anyway.

            AFAIK 4G relies on triangulating a phone’s location. So it’s probably just a couple of lines of code.

            On the other issue though, yep, there is far far far too much distracting crap in cars these days.

            Maybe for people who are particularly independence-minded, you can set the phone to still work while you’re moving, but it disables the airbags.

      1. Yeah 1921 would not be a good year to compare to, too many other variables have changed. However you could compare it to like 2000 or something, I was still using Mapquest at the point I’m pretty sure. And that can’t be safer than GPS because it can’t dictate the turns to me.

    1. Preeetty sure people swerve like idiots without GPS… Personally I would be f-cked without GPS. My brain is broken when it comes to having a sense of direction so GPS is my saviour (just need it for indoors as well). And I find that I plan even more in advance with it. I keep a close eye on how far I need to go before the next turn/lane change and make sure I’ve done it waaay ahead of time because I’m “afraid” of being stuck in the wrong lane and get lost…

      1. This. Although I don’t rely on it turn-by-turn, it forces me to plan ahead rather than risk turning way too late. Street signs are not very well maintained where I live.

    2. “If GPS satnavs weren’t avilable it would certainly improve driving standards.”

      Yes indeed. Gone would be the inconsiderate drivers, because they would be mostly dead after crashing while trying to read a map. or to look for a house number. Lets hope this doesn’t happen to be where you are standing.. eh?

      “People might plan ahead and read the 50ft tall junction signs than rely on a little box and swerve across traffic at the last possible moment without thought for anyone behind them.”

      Or..they might be the exact same kind of drivers, without GPS as they are with one less thing to occupy their attention..

      “If people cannot function at all without technology to do it for them, more fool them.”

      If people blame technology for ignorance and indifference in others, more fool them.

      GPS is a tool.
      The internet is a tool.
      A smartphone is a tool.

      And sadly.. so are you.

      1. In the old days of maps if you missed the junction because you weren’t paying attention you’d more than likely drive on to the next one.
        Now you’ve got a little box that tells you you are going to miss it. So jam on the brakes and take that exit.
        Or worse, back up because it tells you that it’s a 20mile detour so reversing will save you time.

        Yes, GPS doesn’t make fuckwits any more inconsiderate. It just enables them a lot more to be that way.
        Because some people rely on it to replace what they themselves should be doing: paying attention, reading the road, etc.
        Some people will blindly follow their satnav into the sea – read the news at all ??

        If you cannot fathom how technology is enabling people to be more ignorant and less considerate then sorry chap the ignorance lies with your good self.

    3. I wonder what the net effect of GPS navigation is on overall car emissions.

      On the one hand, it makes routes more efficient and reduces wrong turns, etc. I remember days when you’d miss a highway exit, if you didn’t know the mile marker you could drive for 20 miles before realizing it.

      On the other hand, people are more confident to jump in their car and drive somewhere unfamiliar, so maybe it has added trips that otherwise wouldn’t have happened.

    4. If you swerve across all lanes to make a last minute turn with GPS, then you are doing it wrong. I had more issues when driving blind, or in the past with a hand drawn map. I did try at least to indicate landmarks or earlier exits/intersections so I knew it was approaching, but it was an imperfect system.

    5. You don’t fix stupid people by increasing the governments reach/control over all people. Same goes for allowing private entities/corporations to force a users legally owned device to act in some way or do something they did not OK and I don’t mean OK’ing via some legalese Terms Of Conditions that no one reads because they are written to be difficult to understand. Terms of Service and Agreements often use all caps and similar techniques to obfuscate the meaning of the thing.

      More Laws/Government Control Safety !

    6. With a GPS I can see where the street is supposed to be well before I am there.

      With directions I don’t know where I’m going until I see the road sign.

      So I really don’t see how having less information where you are going makes you a better driver.

    1. I was going to say that aluminum foil would be the simpler solution, but jammers would most likely be used where the GPS (and particularly its roof antenna) are hard-mounted in a vehicle and foil hats would be difficult.

    2. dudes like this – GPS jammers are frequently used by truck drivers

      I would about 2-3 times a year help with some dude doing exactly this. We would have the terminal manager make a loud example out of one driver and the rest usually fell in line quickly. We made it perfectly clear we can tell. It is dead easy to tell. The truck is going 60MPH passed through dozens of cell towers (which also have a form of GPS) and yet the GPS still says the truck stop 100 miles ago. How very odd… The terminal managers who liked to give the benefit of the doubt would do a ride along and magically the driver was 2-3 hours ahead of schedule. With a nice stern warning of ‘we know dont screw up again’. The ones who usually got fired were the ones after 2 total equipment swaps and it would fail in the same way every time and after a ride along. Some managers would do a dual set of hardware and track it in a different way then show it. Or a camera to watch them disable it.

      Our favorite was to scare them into leaving the thing alone. “I can put a bucket over that thing and hahaha no signal” “well you could but it has enough energy to bounce the data off a satellite I sure would not want to expose my balls to that” A lie sure but plausible enough they would stop doing it.

      1. And if that theatres structure and or location resulted in someone’s signal being unavailable would that mean that the theatre is at fault if that patron needs to access emergency services?> or should it be on the patron to seek alternative means like going to the theatre mgt and asking them to call emergency services?

        I get what wiretap would use such a device in a theatre. Its not like loud patrons where you can get mgt to ask them to quiet down or leave. Too many people are disrespectful of others and thus do things that cause problems for others and because of there “F’ em” attitude others like wiretap are forced to empty counter measures. Ever been at a theatre where some idiot has brought they’re baby/toddler to an adult movie and the baby/kid cries most if not the whole time?

    1. Because fuck that guy with his on call phone set to vibrate. He didn’t need to be alerted that he has to get the backup generators running for the water treatment plant. Who even needs those?

  4. Any kind of RF jamming equipment is illegal in the USA, and probably in most other jurisdictions also.
    There, somebody had to say it.

    That being said, I’m surprised at how such a simple circuit could produce such a clean output. NO harmonics? None at all? Have the laws of physics looked the other way, or is there far more filtering going on than just what we can see?
    Of course, the spectrum analyzer screen shot doesn’t actually show the frequency where the 2nd harmonic would be expected, right around 3150 MHz, in a part of the spectrum reserved for space research and radiolocation…

    1. I have no insight into the equipment that was used to generate that spectrum graph, but I suspect it’s a very reasonable possibility that the equipment didn’t go up to 3.15Ghz, very possible a failure to measure created the opinion that it must not exist.

  5. Okay, if jamming is this easy, what about spoofing? It would be a lot of fun to have whoever’s watching think you’re in the middle of the Pacific Ocean one minute and downtown Des Moines the next, particularly when you’re supposed to be in London.

    (Yes, I know this kind of signal manipulation would be very difficult…but that’s what makes it fun)

  6. You say that now but when waves of autonomous killer drones are headed your way you’d wish you had an array of these in your go-bag ready to deploy. Although random location spoofers might be more suitable.

    1. If you can get to it. GPS in vehicles, particularly ones where the owner isn’t the driver (trucks), is often hidden away somewhere hard to get to. And they don’t always tell the driver where. Since the machine’s job is to spy on the driver, they’re intrinsically enemies. And a sneaky company might put 2 GPSes in. A jammer solves that problem.

      If the driver was in charge of the GPS, he could just not fit it in the first place!

  7. If the GPS is in the roof of the car, get a rubber magnetic stick on to cover it up. The stuff in magnet should be a poor window to RF. Better to laminate some “tin foil” on it.

    1. Sure you can get something that blocks GLONASS’s frequency though right? But yep, certainly in mobile phones, anything with GPS usually has GLONASS too, they put them in the same chip.

      1. Some receiver might use multiple bands of each system too (not sure about consumer product, but my survey-grade GNSS do use multiple band). That’ll sure make jamming even more complicated.

  8. A running SJCAM 4000 (possibly any other cheap gizmo with LCD) placed closely to GPS antenna makes a quite good GPS jammer. People that do HABs know this. The RF crap is apparently generated by that thing come from (most likely) poorly terminated LCD control lines.

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