cell (mobile) phone scrambler jammer

Can anyone offer some tips on building a cell phone jammer. There are apparently no laws about this (yet) in the country where it will be used. Purpose is to interupt/disable these devices during doctoral thesis dissertations in a typical lecture hall. Ideally an incoming signal would not be detected by the phone, so no ring signal, and also there should be no way to ring out. I can build simple circuits if someone can point the way. I am currently a bit hesitant to dish out hundreds of dollars each for the commercial products and am thinking that this might actually be not much more than a simple radio broadcasting a loud dirty signal (something I could build very cheaply).

Dominic

The mobile phone has been around for a long time now and these low-tech solutions based on audience honesty have never worked. We post signs, we remind people several times before and during the defense and the problem persists. Quite frankly, there are a lot of very rude inconsiderate people in academia who think their mobile phone calls are so important that these rules do not apply to them. I have proposed fines, which are being considered, but are not likely to stop this problem. I have read that some Mexican churches now have these jammers and they are working great. No one can receive calls or call out and the system seems to stop pretty much all attempted connections, which is what I want.

Since this is an electronics newsgroup, I am very interested in the electronics solutions. This industry gave rise to the mobile phone, and I think the jammers it gave rise to seem to be a very efficient surefire accessory. So, has anyone here built a jammer?

Dominic

Dominic, I think screening is your best option. Plus, it is not illegal, at least not anywhere I can think. Basically you construct a Faraday cage around the area you want to protect, so that any RF transmissions are absorbed and grounded out so that cell phones, radios, or any other device that use RF frequencies cannot be used.

Unfortunately, most of the people here in the forum live in the United States, and as my interpretation of the law reads, it is illegal for a private citizen to operate a jamming device(although the military uses them, of course). That is why many people will not be able to provide you with your requested information, as doing so would probably break the law relevant to our country, even if it is not illegal in your country. Sorry, but that's how things work.

Like I said, though, building a Faraday cage would probably be the simplest solution. It requires no power, and protects ALL radio transmissions, not just cell phone freqs. Plus it has the excellant benefit of not being illegal, and as I am told, is being used by many fancy resteurants here in the US to protect against noisy and obnoxious cellphone users.

As for the actual construction, I've heard that using a ferrite coating on plywood has enough strength to absorb the signals without building a potentially more complex Faraday cage. I believe the magazine Popular Mechanics has an article about the subject a couple months ago.

Anyway, hope that helps, and hope you can safely and legally accomplish your goals without anyone getting into trouble. Cheers!

-J

"Dominic-Luc Webb"

** You are asking folk to get involved with breaking the law if they supply such info in a public forum. ** Irrelevant - see above.

** YOU have no way at all of building a successful cell phone jammer.

Commercial offerings are FAR more technically sophisticated than you naively imagine.

......... Phil

So eject them !

Graham

RF screening of the hall will do this. I beleive that this method is now being commercially adopted in some places.

Graham

I am not asking anyone to break any law. I am asking for legally accessible information for legitimate construction and use of these devices that are otherwise sold commercially and used quite legally. I recognize that in some locations there are laws restricting these devices, just as there are places where telephones and phone books are illegal, but this does not apply to the entire universe. If you live under such a fascist regime, do not take part in this thread. I definitely do not want anyone to get tossed into a trash can and burned alive on my account.

As for others, thanks for contacting me offlist. I look forward to more ideas.

Dominic

Or just give the ushers long sticks....

;-) Rich

OK, please post a link to one of these devices, and we'll see what we can do.

And if there _is_ such a thing available legally in the US, and you don't have the wherewithal to control the children, then just buy one and let the children run wild while you jam their phones. Sheesh!

Good Luck! Rich

Thanks Graham for this tip. Investigating jamming elsewhere I see that one important consideration is that whatever mechanism is installed cannot interefere with the complex electronics found in modern lecture halls. This seems to be the situation at my instituion. Aside from the more well general annoyance, at least some mobile phones interrupt some of the audio-visual systems, effectively stopping the speaker dead in his tracks. In fact, it seems that some phones manage this task even without being connected to another phone, in which case the batteries have to be removed. Rather irritating for a large lecture hall to wait for one person to remove batteries due to interference, then a few minutes later wait for another person with another phone that interferes with another piece of equipment. So it seems, the plot thickens, and the solution will be quite more complicated.

I will look into the RF screening. Thanks bunches!

Dominic

This is my understanding. It is interesting that the sources for me to buy the jamming devices are all in the USA. I get the idea they are either not illegal to own or the government is not actively pursuing abusers. I do not understand how the information about how they work or how to build them would be made illegal, but apparently this is the case. Historically, such regulatory endeavors have been dismal failures. If someone knows specifically where these laws can be found in black and white (FCC???) that would be helpful since there are a lot of liberal re-interpretations of laws amongst laypeople. I am not familiar with American laws, but can guess this is governed at the federal level.

The RF screen sounds like basic physics. Just a matter of knowing what materials give most cost effective screening. It might even protect audio visual equipment inside a lecture hall from ambient mobile phone noise. Quite interesting.

Well, if so, this certainly sounds pretty cheap and plywood has been used for walls. I will do some looking around. Giving the simplicity and demand for such things in such environments, maybe there is already a commercial source of building material.

Absolutely, Juno!

Regards,

Dominic

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Jamming involves operating a radio transmitter. There is no other way.

In most (if not all) countries, subject to some exceptions for (very) low-power, approved devices, it is illegal to operate a radio transmitter without a license.

I am not personally aware of any country in the world that allows unlicensed operation of a transmitter. Some have *very* dire penalties.

Apply for a license for the equipment you wish to use, in the jurisdiction where you wish to use it, and see what happens.

--
"Electricity is of two kinds, positive and negative. The difference
is, I presume, that one comes a little more expensive, but is more
durable; the other is a cheaper thing, but the moths get into it."
                                             (Stephen Leacock)

The OP is not in the US, and this is not a US-specific NG.

** Yes you are - f*****ad.

** That cannot be done legitimately on a PUBLIC FORUM !!!!!!!!!! ** You are a raving NUT CASE !!! ** You are a raving NUT CASE !!!

• I got a few suggestions for where you can go and what you can have done to you.

IDIOT.

......... Phil

"Juno"

** Cage a whole lecture theatre ??

That idea is very expensive and full of problems.

If the OP lives where using jammers is legal - then he knows what to do.

Buy one.

......... Phil

ferrite coating sounds like that paramagnetic paint (magnets stick to it) I've no idea what that stuff costs but I feel the bill to paint the walls and ceiling of a lecture theatre (and then re-paint in attractive colours) could be thousands of dollars.

it migt be cheaper to put a microwave oven on the bench up the front and cook any phone you see being used.

Bye. Jasen

I do not claim to know US laws. I know that I had no problem finding them, so you can do the same. It seems by some accounts that it is illegal to give information about these devices, so I had better not do this. Given that they are so easy to find, I only postulate that the laws are not vigorously enforced or that it is not illegal to actually own them. This is why I inquired about the specifics of the relevant laws.

Dominic

Yeah, loads of us (not me personally, of course) have built them. But no one with an ounce of sense is going to admit to it. They're particularly useful in railway carriages, BTW. ;-)

--

"What is now proved was once only imagin\'d" - William Blake