Teardown: Mini GPS Jammer | Hackaday

If you take the time to troll eBay to disassemble interesting electronic devices, you’re sure to start seeing suggestions for some questionable gadgets. That’s how I recently found out about these little GPS mufflers that plug directly into a car’s 12 V socket. Sent to your door for less than $ 10, it looked like the perfect device to open in the name of science.

Now you may be wondering what legal uses such a device can have. Well, as far as I know, there are none. The only reason you would want to mute GPS signals in and around a vehicle is if you’re trying to get away with something you shouldn’t be doing. Maybe you’re out driving a tracked company car and want to enjoy a quick two-hour nap in the parking lot, or maybe you want to deactivate the built-in GPS of the car you just stole, long enough to take it to the store. for cutlets. You know how a man does it.

But we will not dwell on the potentially vile reasons why this device exists. Hackers have never been too picky about the devices they explore and experiment with, and there’s no reason to start now. Instead, let’s take this part of the gray area of ​​test drive hardware and see what makes it stand out.

Can you hear me now?

While the average altitude of the GPS constellation of 20,200 km (12,550 miles) may not be as high as communications satellites in geosynchronous orbit, they are still a long way off. Given this incredible distance and the size of the antenna on most devices equipped with GPS, it is no wonder that the received signal is very weak. So weak in fact that it is usually under the noise. Only with intelligent algorithms and the silence of the wizard can your phone turn this whisper of the stars into something resembling useful information.

When viewed from an RTL-SDR, the GPS signal is like a needle in a haystack.

It is this fragility that makes this type of cheap muffler possible. It doesn’t take much to beat the legal signal. Keep in mind that a device like this is not trying to mimic a GPS satellite, but is just emitting such loud enough nonsense that the real satellite can no longer be heard.

With the muffler on, we can clearly see how the already scarce signal is completely erased from the patterns emitted by the device.

When the muffler is on, the signal is converted into a needle in a haystack.

There is simply no competition; the legal signal is tens of thousands of miles away, and this thing screams with its head away from the hand. I did not test the range of this device, mainly because I did not want it to be powered longer than necessary, but it is certainly able to do the job at least a few meters.

Betrayed by an old friend

Now that we have done it violated federal law in minutes by working with this device (seriously, don’t buy one of them) and make sure the crap does what it’s advertised, all you have to do is open it and find out how it works. For the $ 8 I paid for this unit, I certainly didn’t expect much inside, but it’s still fascinating to see how easy it is to cause so many problems.

After years of losing his job to the Arduino, the 555 timer came in the wrong crowd.

On one side of the PCB we can see that there are only two main components, a 78M05 regulator to lower the car’s 12 volts to 5 volts, and the hacker’s old friend, the NE555 timer. It’s a shame to see that it is necessary to break an illegal muffler before we see one of the most iconic integrated circuits in the history of electronics, but here you are.

Still, unless you want to mute the AM radio, the 555 won’t turn it down. Turning the board, we get our first look at the real problem maker.

RF sorcery in a box

Apparently this component, labeled 13BA A041, is the star of the show. But what is this? Although I could not find a datasheet for this specific model, what we are looking at is a voltage-controlled microwave oscillator (VCO). The visible top plate is actually a metal shield and with a little conviction we can look inside to see the amazing set of components packed in the 9 mm x 7 mm area.

The basic theory of operation here is that the control pin of the VCO (labeled VC on the silk screen) is connected to the output of the 555 timer on the other side of the board. The signal coming from 555 modulates the output of the VCO, causing the noise we see in the center of the GPS frequency of 1.575 MHz.

With the band connected to the VC pin, we can see the 133 kHz signal produced by timer 555. If you had to adjust this signal, you could move around the frequency range on which the muffler operates, albeit without a datasheet. for a VCO, it’s hard to say how far you could push it in any direction. But since these were probably the cheapest components available, probably not far off.

It is also worth taking a closer look at the small four-pin device at the top of the Q6 board. Located directly in the path of the high frequency signal, when passing from the VCO to the central pin of the antenna connector, this would be a logical place to place an amplifier. Although this may be some kind of diode to protect the electronics from anything taken from the antenna.

An unfortunate surprise

Part of me assumed that the Mini GPS Jammer just wouldn’t work, or at least would work so badly that it wouldn’t be a problem. But no, out of tradition, a cheap imported device from eBay actually managed to exceed all my expectations.

Not that I’m happy about that. Of course information for building a muffler like this has been out in nature for years, but you still had to have the means to actually supply the parts and assemble it. With such a low entry bar, this device is obviously quite dangerous in the wrong hands. Although WiFi or a cellular jammer might pose a more immediate threat, it’s still not a technology that anyone wants to reproduce.