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# How to Build: Cell Phone Jammer

Cell phone jammer is an electronic device that blocks transmission of signals between a cell phone and a base station. By using the same frequency as a mobile handset, the cell phone jammer creates strong interference for communication between the caller and receiver. It is effective in blocking transmission of signals from networks including UMTS, 3G, CDMA, GSM and PHS.

Mobile phones operate at different frequency bands in different countries. For Canada, the 1900 MHz band is the primary band, particularly for urban areas. 850 MHz is used as a backup in rural areas. USA uses 850 and 1900 MHz bands, depending on the area. Europeans tend to use the GSM 900 and 1800 bands as standard. Middle East, Africa, Asia and Oceania also use these frequency bands. In Russia and some other countries, local carriers have licenses for 450 MHz frequency to provide CDMA coverage.

The use of different frequencies makes it difficult to have a jammer for all frequencies. However, the below mentioned formula can be used to calculate the required values.

### F= 1/ (2*pi*sqrt (L1*C1))

Depending on the frequencies you need to block, the values of the inductor (L1) and capacitor (C1) can be altered.

For example, if mobile phones at your area work at 450 MHz, you need to generate 450 MHz with some noise to act as the blocking signal. Now the cell phone receiver will not be able to understand, which signal to receive. We have successfully blocked cell phone signals.

Here, 450MHz is the tuning frequency. Cell phone jammers for other frequency ranges are designed similarly. However, the signal range is very weak. Thus, this circuit works only for a range of 100 m.

# Description:

For any jammer circuit, it’s essential to have three important subcircuits.

These 3 circuits, when combined together form an efficient cell phone jammer circuit.

# Working

• RF amplifier circuit comprises of the transistor Q1, capacitors C4, C5 and resistor R1. This RF circuit amplifies the signal generated by the tuned circuit. The amplified signal is given to the antenna through capacitor C6. It blocks DC and allows only the AC component of the signal to be transmitted.
• When transistor Q1 is turned ON, the tuned circuit at the collector turns ON. The tuned circuit consists of capacitor C1 and inductor L1. This acts as an oscillator with zero resistance. It produces very high frequency with minimum damping.
• When the circuit is ON, voltage is stored in the capacitor. Once the capacitor is completely charged, it allows charge to flow through the inductor. When current flows through the inductor, it stores magnetic energy corresponding to the voltage across the capacitor. At a certain point, the inductor reaches its maximum and the charge or voltage across the capacitor turns to zero.
• Now the magnetic charge through the inductor decreases and the current charges the capacitor in opposite or reverse polarity. The process repeats and after a while, inductor charges the capacitor and becomes zero.
• This process runs till internal resistance is generated and the oscillations stop. RF amplifier feed is given through capacitor C5 to the collector terminal before C6. The capacitors C2 and C3 generate pulses in a random fashion (noise) at the frequency generated by the tuned circuit.
• The RF amplifier boosts the frequency generated by the tuned circuit. The frequency generated by the tuned circuit and the noise signal generated by the capacitors C2 and C3 is combined, amplified and transmitted.

# Components Required

 COMPONENT USAGE Resistor R1 Emitter Loading Resistor R2 Base Biasing Capacitor C1 Frequency Generation Capacitor C2 Feedback Capacitor C3 Feedback Capacitor C4 Noise Reduction Capacitor C5 Coupling Capacitor C6 Coupling Capacitor C7 Decoupling Transistor Q1 Amplification Inductor L1 Frequency Generation

# Note

• This circuit can block signals only within a 100 meter radius.
• Usage of this type of circuits is banned and illegal in most countries.
• This circuit is also used in TV transmission and remote controlled toys.
• If the circuit is not working properly, try increasing resistor and capacitors values in the circuit. Use the formula

### F= 1/ (2*pi*sqrt (L*C)).

• Power supply for the circuit should not exceed 3 Volts.

More interesting projects are available at: DIY Electronics Projects.

Note: The cell phone jammer is an untested prototype circuit and banned in several countries. Keeping in with those regulations, we might not be able to help you out with the exact values.

This article was first published on 17 October 2017 and was recently updated on 30 November 2018.

• Dear Krishna, Since this is banned in some areas, this is just a prototype to give you an example.

• Dear Blue zee,

This is only a prototype circuit, as of now we do not have the source code for this article.

• Prototype is just an idea for the circuit. You can create the circuit as per your liking with measurements from anywhere. We can’t guarantee that the project would work but the concept is sound.

• Dear Adarsh, this is just a prototype circuit. All the required information is already provided in the article.

1. Comment:
Good day pls. give me a simple diagram of a signal jammer with parts that are available in the market…
I intend to use it for blocking wifi & moble phone signals…

• You can’t jam WiFi signal, Because WiFi is work on 2.422 GHz so you can’t generate this frequency from tank circuit by component which is available in market.

2. please tell me what the output of C6 Then is possible to simulate this circuit in proteous 8.0

3. is it possible to simulate on proteous

4. sounds and looks like a good idea. My daughter is doing some home work and needs literature on making phones. I found your work sound easier I hope it will help her.

5. Whats the use of this if it is not working. I need the the working circuit plz. Can u upload it??

6. If already have a jammer, how to improve its working range?
I bought a jammer on perfectjammer.com , but I found that the interference range is not enough. Can I improve the interference range by modifying the circuit?

7. I really like your teaching on how to make cellphone jammer. Thank you so much.
But I need your help to complete my project. P/s how can I get the jammer complete circuit?
Thanks.

8. I am looking for acircuit diagram for a transistor servo circuit complete. In my country you won’t find servo or its ICs.

9. Please any one explain the concept of mobile jammer and how it works?? Please Wednesday I have seminar, so please give explanation… Quick

10. Hi it’s sanjid from Uk would u able to make me mobile signal jammer
An if u do how much will u charge me
Thanks

11. I am amazed at the people commenting on here. If you have read the 20+ times that the team has said this is simply a concept a.k.a. =
a prototype. And if you do not know what a prototype is and yet have the ability to post the question, you then also have the ability to search the internet for the answer. This is not for entry level or rookie skill level. If there is anything unclear to you here then this is simply above you skill level. You need senior to expert level experience and knowledge of Electrical, RF, PCB and/or telecom. Engineering

• Exactly, and what makes me wonder is why they are all in such dire need of such a device?
They should not be messing around with RF transmitter circuits in the first place. This is a fine example of people, “knowing just enough to be dangerous!”.

They may as well take an old microwave oven apart, grab a hold of the magnetron, and aim it at their victim and fire it up!
Opps, maybe I shouldn’t give any ideas like that! Lol 😂

12. What about CDMA, W-CDMA and LTE,etc.. will it work properly because these technologies uses spread spectrum rather than a single frequency.
I want to create one for 2300 mhz. So to increase the frequency only L1 and C1 has to be changed or any other components as well like R1,C7,etc ?

• heyyy hii have u done this? i need ur help plz give me fullly details about it annnnd as this is my project i need to completee soon lease help me in completing this….and finnally did it work

13. The transistor bf 494 is working on 250mhz.if you want to make rf oscillator for 450mhz then you first replace the transistor. As a basic circuit this is a good circuit.

14. The operating frequency of transistor bf 494 is 250 MHz,if you want to make rf oscillator for 450mhz then you replace the transistor. As a learning purpose the circuit is good.

15. Hello,
I think there is a mistake and the colector should not be connected to ground, otherwise the DC will be short circuited -assumming an ideal coil of zero resistance.

16. Note for dummies: I finally got it… the line from C5 to C6 is not connected to ground -it crosses over but there is no black dot 🙂

17. Yaaah u are really right of the circuit diagram u just display but it is too noisy asas compared to how u said the c4 reduceses noise but rather the sound more inflicted within the circuit. I did I project which will be able to provide a mosque with LEDs display .after some time I got to know dat , mobile phones ring and bells in the mosque where by we are praying .
So I decided to make a stop to it by making it work so jamm the signal range within the mosques not any other place , so I made several research about how to jamm mobile phones , so I made research and it brought me through success and I was able to make it, but unwantedly it affects the microphone player system within the mosque with made the speaking more difficult and the sound was not spicing out well but rather created a radio active signal noise piiiiiiiiiiiin

18. You say the target freq. for the circuit is 450 Mhz but for the given inductor and capacitor C1 it would generate a ~277 Mhz signal, am I missing something?

19. Hello there. I want to make a mobile signal jammer like this for a autistic child. He spends his time most of on useing mobile phone and he is start to act rude and attacker. He playing games and watching videos online. Actually that videos have violence and more. So the kid becoming to dangerous person. All i want make a simple and tiny circuit for block phone cell in 2 squaremeters. Can you please help me ? i tried this circuit but this doesn’t work. if you help me, we will be greatful to you. thanks alot. with all respect.

20. You say the target freq. for the circuit is 450 Mhz but for the given inductor and capacitor C1 it would generate a ~277 Mhz signal, am I missing something? Or how can i amplify it to 450mhz thanks

21. Since resistor and capacitor values are not given and or listed. Good luck making a “working” prototype. It’s like playing Russian roulette.

22. The Circuit looks more line a FM Mike. Except for the feed back component, C5, all are almost identical.

23. Sir, you have said that it is just a prototype.According to my knowledge, even it is a prototype but it must be true and should work.
But why are you saying that i don’t guarantee for working.
Is it wrong circuit??

24. The jamming system transmits adequate power radio signals to cut-off communications between cell phones and cellular base-stations.Mobile Jammer is available in different models depending upon the output power.
Upon activating Cell phone jammer, all idle phones will indicate “NO SERVICE”. When the cell phone jammer is turned off, all cell phones will automatically re-establish communications and provide full service.

25. By solving the equation I found 277 MHz frequency how can you say that this circuit is working for 450 mhz frequency

26. If I increase or decrease the range, then what should I change ? And how can I know what should be the appropriate value of components for that specific range ?