We shared our knowledge about how to make a jammer yourself last month. In that post, we list a step-by-step guide to building your signal jammer that can block the cell phone signal. Today, we will share with you how to build a GPS jammer.
So without further ado, let’s get started.
Before seeing how to make a GPS jammer, you must first know some basic notions in the world of electronics that we will detail in this post to be able to make your own. So the first thing to ask yourself: what is a GPS jammer?
What is a GPS jammer?
It is an inexpensive but high-tech device to temporarily disable reception of the civilian course acquisition (C/A) code used for Standard Positioning Service (SPS) on the Global Positioning System (GPS/NAVSTAR) L1 frequency 1575.42 MHz.
This is accomplished by transmitting a narrowband Gaussian noise signal, with a deviation of +/- 1.023 MHz, on the GPS L1 frequency. This technique is a bit more complicated than simple continuous wave (CW) jamming but tends to be more effective (i.e., harder to filter) against spread spectrum radio receivers.
This device will not affect the precise positioning service (PPS), which is transmitted on the GPS L2 frequency of 1227.6 MHz and has little effect on the P-code, which is also carried on the L1 frequency. It can be a problem if your particular GPS receiver needs to have the P(Y) code through the C/A code before proper operation.
This device will also not work against the new upcoming GPS L5 frequency 1176.45 MHz or the Russian GLONASS or European Galileo systems. It can be adapted to jam the new civil C/A-code signal, which will also be transmitted on the GPS L2 frequency.
So it will work against most consumer GPSs, provided they are not configured with an advanced anti-jam system.
Why make a GPS jammer?
Several manufacturers now sell “hidden” GPS-based tracking devices mounted indoors. Some transmit your contact details via your Smartphone or vehicle, itineraries, and movements without your knowledge.
Car rental companies have been known to use GPS tracking devices to check that you are not going too fast and misusing their rental vehicles. The unsuspecting renter often faces these hidden abuse “charges” after the rental vehicle is returned.
Cell phone companies, trucking companies, private investigators, toll roads, airplanes, and many more, all of these services fully participate in the use of GPS tracking. The problem is you don’t want everyone to know where you are.
How to make a GPS jammer
This will briefly describe each of the main sections of the entire jamming device and how to put them together to make a GPS jammer.
The main components of the GPS jammer consist of a Motorola MC145151, a phase-locked loop (PLL) frequency synthesizer chip, a Micronetics M3500 chip, a 1324S voltage-controlled oscillator (VCO) module, and a division of the Fujitsu MB506 -by-256 Prescaler chip.
The VCO feeds part of its radio frequency (RF) output signal into the divider chip, where it is divided by 256. A 1575 MHz signal would be transformed into a 6.15234375 MHz signal. This is then fed into one side of the PLL Chip.
The other side of the PLL is fed with a reference frequency derived from a 10 MHz quartz crystal. This crystal reference frequency is divided 512 times by the PLL to reach 19531.25 Hz. The 6.15234375 MHz Prescaler output frequency is divided 315 times by the PLL chip for a final frequency of 19531.25 Hz. This will be the new PLL internal reference frequency. That big bad 1575 MHz microwave signal now looks like just audio frequency from the PLL chip.
The PLL chip internally compares the phase of the VCO side 19531.25 Hz signal to the phase of the crystal side signal of 19531.25 Hz. The PLL chip produces high or low voltage pulses depending on whether the crystal signal is leading or lagging the VCO signal. These pulses are then filtered and attenuated into a pure DC control signal via a simple passive loop filter. This cleaned signal is then connected to the VCO voltage of the control input.
When everything is working correctly, the VCO output frequency is locked to whatever frequency you have programmed into the PLL chip, 1575 MHz in this case. It will stay on that frequency even through dramatic temperature changes, a problem a non-PLL VCO might have. If the PLL is not working properly, the red “PLL Unlock” LED lights up.
Due to the quirks of using cheap and easily obtainable components, you will need to modify two load capacitors on the reference crystal. This is unusual but necessary to move the signal from the default 1575 MHz frequency to the more appropriate 1575.42 MHz (+/- a few hundred hertz). This is a very important and delicate procedure; you will need a frequency counter to accomplish it.
The GPS jammer noise generator is very simple. A 6.8 Volt Zener diode is first biased, buffered, and amplified by a single 2N3904 transistor. This single Zener diode can generate broadband and noise signals from audio frequencies above 100 MHz. We then filter that noise signal down to something more practical and something the VCO module can also respond to. This is done via the LM386 audio amplifier chip. The LM386 amplifies and filters the final noise signal. The final output signal of LM386 will have enough time if you need to adapt it to a wideband noise GPS jammer.
This low-frequency noise signal is sent through a 100 Ohm potentiometer to a simple resistor/capacitor network, which is mixed with the VCO voltage. It sets the control signal (described above). The single 1N4148 diode prevents negative voltage pulses from reaching the VCO.
This mixing results in a new “noisy” supply of the VCO’s voltage adjustment control signal. The resulting RF signal looks like random noise dancing around the central 1575.42 MHz RF carrier. You will need to set the deviation of this noise to approximately +/- 1.023 MHz from the 1575.42 MHz RF carrier. Access to a spectrum analyzer is required to do this properly, or you can use an oscilloscope and the included test point voltages to get a rough setup.
The +7 dBm (5 milliwatts) RF output of the VCO is first slightly attenuated (4 dB) and harnessed for the input of the MB506 pre-converter. It then passes to the RF amplifier and bandpass filter stages. The first RF amplifier is a Sirenza Microdevices SGA-6289. It offers approximately 13 dB of gain to overcome losses from resistive buffer attenuation. It also shows a good 50 Ohm termination for the VCO RF output and even helps drive the final RF amplifier.
The GPS bandpass filter is a Toko 4DFA-1575B-12 2-pole ceramic dielectric filter from Digi-Key, part number TKS2609CT-ND. This part is optional but helps clean up the RF spectrum before further amplification. The insertion loss of the filter is about 2 dB.
The final RF amplifier is a WJ Communications AH102. It provides another 13dB of gain, with a higher P1dB compression point of about 27dBm (500mW). The AH102 draws the latest current from any room and isn’t necessary if you’re aiming for low-range, low-current battery operation.
Voltage input regulation and filtering are made using standard voltage by IC regulators. LM2940CT-12 12 Volt, 1 A Low Dropout Voltage Regulator is used to regulate the 12 Volt main line. Standard 78xx series regulators are used to supply the 9 and 5-volt lines. A simple diode/fuse polarity protection scheme is also provided on the battery input. The use of a self-resetting fuse is strongly recommended.
You can turn off the GPS jammer with a common 12-volt rechargeable battery. Radio Shack’s 12 Volt, 4.5 Amp-Hour Lead-Acid Battery, part 23-289, is a good choice. Old car batteries, 6-volt strings, lantern batteries, or even solar panels will also work. The current draw for the completed GPS jammer will be around 300 milliamps.
A radiating antenna is not shown in the schematic diagram and must be purchased or constructed for proper operation. Many commercial GPS receiving antennas will work well for this low-power transmitting application.
The LPY2 log periodic Yagi periodic antenna can be used for radiating directional applications (straight line transmission). Using a directional antenna will give you a slight increase in overall transmitted RF power, which increases the range of the GPS jammer and can also be used to protect your GPS receiver from being jammed.
The bottom line
We know it isn’t easy to follow all these steps and especially find all these parts, but at least you know how to make a GPS jammer and how it works. You can buy a high-quality GPS jammer in our online store if you don’t want to make it all yourself. We are offering free worldwide shipping and a one-year warranty now.