Modifying a Cheap Portable Cellphone Jammer





Introduction: Modifying a Cheap Portable Cellphone Jammer

This instructable is going to show you a quick process which will allow you to convert a cheap portable cellphone jammer from Chinese frequency's (I think) over to American or other regions frequency's.

Specifically this model from

  • Important Note: Usage and purchase of this item may not be allowed in certain countries. It is your responsibility to check for your local regulations.

Step 1: Dissasembly of the Jammer

In this step we will simply want to remove the top and bottom plates from the outer casing.

You will need:

- A small phillips head screwdriver
- a pair of pliers - optional

The first thing you're going to want to remove is the three antennas because the top plate will not come off properly with them attached. Next, there are four small screws which hold the top and bottom plates to the aluminum casing, remove these screws and then remove the on/off button from the side using the pliers or your fingers, pretty simple.

Make sure you don't lose the screws, put them aside with their respective cover piece.

Step 2: Removing the Inner Circuit Board and Locating the Adjustable Caps.

In this step we will remove the inner circuit board and locate the caps we will be adjusting.

Once the top and bottom plates are removed the inner board will slide out with some slight pressure. Once the boards out you just want to find the 6 small variable capacitors towards the middle of the board.

Step 3: Adjusting the Caps

In this step you just want to adjust each set of caps until you locate the correct band to block out whatever carrier or network you want to block.

in order to adjust the caps its best to use a small screwdriver, either a phillips head or a regular will do, you don't want to use allot of force here as the capacitors are very sensitive to force and could break.

If you have a frequency counter this step will be very easy as you can precisely tune your jammer, without a counter im afraid its pretty much guess and check. The easiest way I have found to do it is to call a number that continuously generates tones or some kind of audio
and then sit about 15 feet away and slowly turn the knobs until you hear the phone drop out

Here are some useful reference frequencies for tuning.

Cingular 1.850-1.865 Ghz 1.930-1.945 Ghz 1.730-1.735 Ghz 2.130-2.135 Ghz

Sprint 1.865-1.870 Ghz 1.945-1.950 Ghz 1.885-1.890 Ghz 1.965-1.970 Ghz

Tmobile 1.895-1.910 Ghz 1.975-1.990Ghz 1.710-1.720 Ghz 2.110-2.120 Ghz 1.740-1.745 Ghz 2.140-2.145 Ghz

Step 4: Reassemble

In this step you just want to reassemble everything. Start by sliding the board back in, then reattach the top and bottom plates with their respective screws (4 each) next remember to place the on/off button back in its socket, and then finally put the antennas back on ( make sure to put the correct antenna on the correct port).

After you have finished reassembling the unit you may find it annoying to continuously need to open the unit up and re-tune whenever you decide you want to block out a different carrier. In that case you can optionally drill out some small adjustment holes with a small 3/16 size drill bit. Make sure to disassemble and remove the circuit board fully before drilling!

Step 5: Have Fun, But Not Too Much!

Just remember, in most places actively blocking any kind of communications is illegal! so if you plan on using this device make sure you check your local laws and regulations.


Thanks to the guys over at PLA for the method, especially NAK (see you in class dude)



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    278 Discussions

    I just got one of these, and the Board looks different than the ones in these pictures (see attached pic). I need help tuning this thing so it at least blocks AT&T and Verizon. I've tried every setting in this thread and in the threads on dealextreme, and none seem to work. I have some questions, such as: What do the hightrim and lowtrim on each variable cap actually mean? Which caps on this new board correspond to which frequencys/carriers? How can I get this thing tuned without a spectrum analyzer or frequency counter? If there's no way around tuning this without a spec. anlyzer/freq. counter, can anyone recommend a good one to buy that will meet the range requirements for the mobile phone? Is there anyone out there that can help me? Please?

    3 replies

    Even a private shop may tip off the Feds, especially if they deal with customers who come in with "broken" phones found to be working just fine, and those customers are clustered in a particular location. A phone shop will work to keep phones running, not help someone illegally shut them down.

    Keep in mind that Instructables is now owned by a major software company Autodesk, who is a member of the scary copyright group BSA. So certainly they have enough lawyers to know that allowing discussion of illegal activities is not the best idea.

    Why must fun things be so illegal. In my class one student texts all the time and would love to have one to tick him off with. Then he would be angry with his phone. Pretty much I would use it on only him.

    3 replies

    In such a case talk to your teacher. Even absent any specific rules regarding specific devices, there still should be a general clause regarding disruptive behavior.

    Stay away from jammers, as these days mobile phone companies are monitoring signal quality all the time for service anomalies, and will investigate anything that doesn't look right. A phone company actually busted a science teacher in Florida about a year and a half ago.

    use a modified annoyatron from think . itill do pretty much the same thing, as well as put wierd stuff arcross their screens.

    lol in my language arts class almost half the class texts and it would be hilarious for them to not be able to

    But what practical use does this have? Anyone who would jam cell phones, is just as inconsiderate as those dimwit cell phone users, who tempt others to use these devices. No one has the right to interfere with the service I and others pay for.

    11 replies

    You are quite right, and as such it is quite surprising that Autodesk (a huge US software company that owns Instructables) hasn't taken severe action against the author of this project for their willful disregard for RF interference law, and potentially for the health and safety of those within range of this illegal device.

    I teach high school and I don't want students texting test answers to one another, You have the right to your service, but not the right to facilitate fraud.

    Can't the schools require students to keep the phones in their lockers, during class periods? Can't any phone found in the class rooms confiscated, to be returned only to a parent that goes to the school to pick it up? Respectfully how can the kids learn self discipline, when the adults in their live justify breaking the rules, when doing so makes it easier?

    just because you make the rule doesnt mean they'll adhere. i was in high school a few years ago, i can say, most everyone who had a cellphone had it in class, even though they were considered contraband. now that i'm in the military, if you get caught with a phone on you in certain buildings, it's a security issue and it will be promptly destroyed in front of your face. saw it happen two weeks ago to this girl who wanted to text during breaks. they smashed her iphone 4 or whatever the hell the newest version is. im not sure if schools could make this rule though.

    Certainly a school needn't to go to the extreme of destroying a phone. Confiscating phones taken into the class room, to be return only to a parent, that went to the school to get it wouldn't be too radical. the adults would be the only ones that would stand in the way of a reasonable action. What happened to the time when caught cheating meant an automatic failing grade on the exam for both parties, and failing the class entirely if the cheating didn't abate?

    As long as it is the posted policy they can.

    Usually 'school policies' are cleared with the districts attorney before posting them.

    Don't be stupid, the mobile phone is an invaluable tool to education, I use mine all the time, for taking notes, to even photographing the whiteboard, but yeah, I hate the kids who just go onto fakebook all the time...

    Man I'm getting old. No modern whiteboard, we called them blackboards, even if they where green. A cheap snapshot camera was too expensive for most kids to have. No matter taking photos with them was more expensive yet. Not mention actually having the photos of the board would be at least a week away if you lived in a rural town. I agree the phones can be a tool for the students to use, and have to see the degree to what the smart phones will become more useful tools for the students. As a student do you have any recommendations as how to deal with the inappropriate use of the phones in the class room?

    I think a bit of common sense is needed with them... Silent mode, full attention paid to the subject of class, and the requirement to put the phones in your bags during tests. If anyone is obviously on facebook, the teacher should proceed to read the contents of the screen out loud to the class, for maximum embarrassment...

    Then again, I am a TAFE student, (the Australian form of College) So phones and other tech are welcomed by the teachers, a zero tolerance high school will not, however...

    ditto to that, and amen ! prisons and schools alike should have them, , short range of course. . 1300.00 will do the job. . for 40 130.00 they get bigger obviously.