If you spend enough time browsing eBay to break down interesting electronic gadgets, you will surely see some suspicious gadget suggestions. This is how I recently discovered these miniature GPS jammers that can be plugged directly into a car’s 12v socket. It can be delivered to your door for less than $10, and it seems to be the perfect device torn apart in the name of science.
Now, you may be wondering what legal uses such equipment might have. As far as I know, no. The only reason you want to interfere with GPS signals in and around the vehicle is when you are trying to get rid of things you shouldn’t do. Maybe you are driving a haunted company car and want to get a quick two or two hours in the parking lot, or you may want to turn off the car’s built-in GPS, and the GPS you stole is long enough to bring it to the car shop. You know how to do it.
However, we will not delve into the potential evil causes of this device. Hackers have never been too picky about the equipment they want to research and test, so there is no reason to start now. Instead, let us use the hardware in this gray area to test the drive and see what it does.
Can you hear me
Although the average height of the GPS constellation is 20,200 kilometers (12,550 miles), which may not be as high as the communication satellites in geosynchronous orbit, there is still a long way to go from them. Given this incredible distance and the size of the antenna on most GPS-equipped devices, it is no wonder that the received signal is very weak. In fact, it is so weak that it is usually below the noise floor. Only with clever algorithms and a little bit of witchcraft can your phone turn from whispers from the stars into something similar to useful information.
It is this vulnerability that makes this cheap GPS Jammers possible. It doesn’t take much to overwhelm legal signals. Remember, a device like this will not try to imitate GPS satellites, but just send out nonsense big enough that the real satellites can no longer be heard.
When the jammer is turned on, we can clearly see how the already weak signal is completely eliminated through the pattern sent by the device.
There is no competition. The legal signal is tens of thousands of miles away, and this thing screams in range. I haven’t tested the range of this device, mainly because I don’t want to open it longer than necessary, but it can perform tasks of at least a few meters.
Betrayed by old friends
By running this device in violation of federal law for a few minutes (seriously, don’t buy any devices), and verifying whether the evil elements have done what is advertised, all you have to do is turn on the device and find out how this works. I certainly didn’t expect much of the $8 I spent on this device, but it is still fascinating to see how easy it is to cause so much trouble.
There are only two main components on one side of the circuit board: a 78M05 regulator that can be used to reduce the vehicle’s 12 volts to 5 volts, and the hacker’s old friend NE555 timer. Before we see one of the most iconic ICs in the history of electronics, it is shameful that illegal jammers must be removed, but this is not the case.
However, if you do not want to interfere with AM radio, 555 will not turn it off. When we turn to the board, we first understand the real troublemakers.
RF witchcraft in a jar
The component labeled 13BA A041 is clearly the star of the show. What is that? Although I cannot find a data sheet for this particular model, it is a voltage controlled microwave oscillator (VCO). The visible top plate is actually a metal shielding layer. With a little persuasiveness, we can look inward and see an amazing number of components installed in the 9mm x 7mm area.
The basic working principle here is that the control pin of the VCO (marked with VC on the screen printing) is connected to the output of the 555 timer on the other side of the board. The signal from 555 modulates the output of the VCO and generates noise, which is concentrated on the GPS frequency of 1,575 MHz.
After connecting the oscilloscope to the VC pin, we can see that the 555 timer is generating a 133KHz sawtooth signal. Adjusting this signal allows you to change the frequency range of the jammer. However, without the VCO’s data sheet, it is difficult to tell how far you can move it. But since these may be the cheapest components available, they may not be far away.
It is worth looking at the small four-pin device marked Q6 on the top of the motherboard. When it goes from the VCO to the center pin of the antenna connector, it is in the path of the high-frequency signal, which will be a reasonable place to place the amplifier. But it can also be a diode to protect electronic equipment from all objects picked up by the antenna.
Unfortunate surprise
Part of me thinks that the mini GPS jammer will not work at all, or at least not so bad that it is not a problem. But no, contrary to tradition, the cheaply imported equipment from eBay managed to exceed all my expectations.
It’s not that I am happy about it. Of course, the information on manufacturing such jammers has been flooded for years, but you still need to master some basic knowledge to actually purchase and assemble parts. With such a low entry bar, it is obviously dangerous to use incorrect hands. Although WiFi or cellular jammers may pose a more imminent threat, it is not a technology that everyone wants to spread.