Mobile jammer (within legal limits)

[HamdyDumpty]

I was trying to design a short range mobile jamming circuit (for academic purpose only and with the permission of the Frequency Allocation Board of the country) and was wondering how I might be able to produce random signals within the bandwidth of the mobile service's frequency.

My general idea has been:

An AM receiver tuned to no particular frequency (in order to catch random signals)
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an AM modulator to modulate the frequency upto the mobile service's frequency
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a bandpass filter filter within the bandwidth of the mobile service's frequency
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amplification
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transmission


Do you think this is a reasonable design or is the whole approach on the wrong track?

Anxious to hear some recommendations.

 

[Someone Electro]

Legal limit is 0mW.Any radio device that disturbs somthing is ilegal

 

[HamdyDumpty]

yeah, we kinda wenty through the procedures through our uni (i live in pakistan). They agreed to it since it was for academic and demonstration purpse only.

 

[Nigel Goodwin]

yeah, we kinda wenty through the procedures through our uni (i live in pakistan). They agreed to it since it was for academic and demonstration purpse only.

Perhaps you would care to scan and post the written permission you have from the goverment authorities?.

I doubt anyone at your University has the authority to give you permission?.

 

[Oznog]

Cell phones are actually fairly hard to jam, there are hundreds of channels a service uses.

Nigel's not alone in abhoring these projects. Seems like every newbie here wants to build one, and not a one of them has any valid reason to operate such a thing. It will only cause a lot of trouble for a lot of people, and be very hard to stop. Even though it's illegal here it would be very difficult to locate and prosecute.

Even people who should know better, like movie theaters and that one guy from a university who wanted to enforce a university-wide no-cell phone policy, want to do it. It's like some kind of friggin addition.

Even for localities where it may not be illegal, I don't like to see propagation of this concept into hobbyist technology as a good thing. As soon as somebody describes their project and put plans on the 'net and high school kid'll start competing to see how many city blocks they can jam. Probably will jam FAA communications too without them realizing it. In fact making a jammer which jams hundreds of channels but does not jam any frequencies outside the specified band is very difficult and not really an amateur project.

 

[Nigel Goodwin]

It's like some kind of friggin addition.

I always said maths was bad for you! :lol: :lol: :lol: :lol:

 

[HamdyDumpty]

I understand your concerns, this was actually suggested to us by one of our professors who cited the example of a local bank that was unable to control its jamming signals. We were wondering if we could think of a way to get around such a problem. The university is government owned and its not very difficult to get an approval through the Director of Industrial Liaison.

It was a very innocent thought with which we began but what i have come to know is that not many encourage this idea. We do have the backing of our professors, now I am wondering if its worth pursuing. We still have a couple of months to the Engineering Fair (to be held on campus). Should I drop the idea?

 

[akg]

but has anyone realy built it..?? :roll:

 

[Nigel Goodwin]

I would suggest (again) a Faraday cage around the building, this causes no interference and (if done correctly) would prevent internal radio signals.

Any transmitter method is going to cover far too large an area, or not cover enough of an area - unless you do it INSIDE a Faraday cage?.

 

[HamdyDumpty]

Ok I just read the other thread on Cell Phone jamming and dunno why I feel like an idiot now :shock: :lol:

 

[evandude]

A professor of mine explained the concept of CDMA to us, which is the way modern cell phones communicate. It's a spread-spectrum communication, and due to the way it works, it can pick the actual signal out of noise quite well. It was originally implemented in some war, and was extremely useful because the signal often does literally reside in or very near the noise floor, making it hard to detect, and was just about immune to being jammed by a strong narrow-band signal like traditional communication schemes.

You might be able to jam it, but you'd probably need a lot of power spread over a large spectrum, and by then your system would be so illegal you wouldn't dare turn it on :lol:

As a demonstration of the power of CDMA, we DO have a faraday cage at my university. And students have been able to make cell phone calls from inside... signal strength is of course reduced, but it still works. In all fairness, it is not 100% done construction as it needs improved earth grounding, but it is still a complete box where you are surrounded on all sides by two layers of sheet metal.

 

[Oznog]

It was a very innocent thought with which we began but what i have come to know is that not many encourage this idea. We do have the backing of our professors, now I am wondering if its worth pursuing. We still have a couple of months to the Engineering Fair (to be held on campus). Should I drop the idea?

Well, yeah. That's what we're saying. In practice there's no good reason to be jamming cell communications outside of wartime.

Actually I heard Israel has used it to counter cellphone-detonated bombs but in practice it's not only difficult to make work, it's rare to actually know when a bomb is placed somewhere and at that point the need is to clear the area. It wouldn't take long before they'd modify the concept to set the bomb off if it became jammed anyways. So you couldn't use it to protect the area until it was cleared of people and you couldn't use it to protect property by preventing it from going off. Thus if such a circuit were used all the jammer would do would be to make it detonate at a predictable time.

It is a somewhat worthwhile process to investigate how the distributed channels of a cell phone can be jammed. That may get you a job with a military contractor though that's pretty darn unlikely. But a more practical result is you gain insight how such a system- or any similar communication system- can avoid being jammed, either on purpose or from stray pirate radio station signals. It is unnecessary and not all that helpful to build a jamming device to explore this area.

 

[anoop_electrical]

i need a mobile jammer circuit..coz i wan to know how it works and i wan to make :lol:

 

[suicidalmonkey]

i need a mobile jammer circuit..coz i wan to know how it works and i wan to make :lol:

Can I ask a question. HOW STUPID ARE YOU?

Search this site, every person who has asked about mobile jammer circuits has replies stating how studid and illegal they are.

A quick google search for mobile jammer and this was on the first result.

SALE CONDITIONS FOR CELLULAR JAMMING PRODUCTS


Note - The use of cellular telephone jamming equipment is prohibited in some countries. It is the responsibility of the customer to ensure that they have the legal right to import these products before purchasing from us. Upon purchasing, the customer becomes wholly liable for any legal issues that may occur as a result of the importation and/or use of these products in the destination country.

Note for UK customers: Cell phone jamming equipment is illegal to use in the UK as it violates sections 1 & 13 of the 1949 telegraphy act, we are therefore unable to supply cell phone jammers to any UK customer with the exception of certain military and government departments who have the necessary authorisation from the UK Office of Communications (Ofcom). Please note that no exceptions can be made on this policy.

Due to non CE approval of these products we cannot sell these products into any European Union country.

 

[Nigel Goodwin]

As a matter of interest I looked at the same site, really funny - it's a UK site :lol:

Yet they specify they can't sell to the UK or Europe, yet give order and delivery details for both areas :lol:

 

[Clyd3]

well, people reading this who still have alterior motives - consider rather the espionage route, it remains easier to listen in on the conversation than to jam, and many are waaay more willing to give out information on this.
As for why people want to in the first place - i can only think it's boredom, get out there in the real world and have some fun.

 

[Hero999]

You don't always neeed an active jammer for example a cinema could line their walls with steel plating to create an effective Faraday cage and block all radio reception.

 

[Nigel Goodwin]

You don't always neeed an active jammer for example a cinema could line their walls with steel plating to create an effective Faraday cage and block all radio reception.

As already suggested previously in this thread, and the many others.

I think it's time this thread died, so I'm locking it!.