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cell (mobile) phone scrambler jammer

Discussion in 'Electronic Basics' started by Dominic-Luc Webb, Jan 11, 2006.

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  1. 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

  2. Rich Grise

    Rich Grise Guest

    Station guards at the doors, and tell the lecturees to turn their phones
    off. Or confiscate them, and give them back after the lecture.

    Good Luck!
  3. 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?

  4. Phil Allison

    Phil Allison Guest

    "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

    .......... Phil

  5. 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.

  6. Phil Allison

    Phil Allison Guest

    "Dominic-Luc Webb"

    ** Yes you are - fuckhead.

    ** 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.


    .......... Phil
  7. Pooh Bear

    Pooh Bear Guest

    So eject them !

  8. Pooh Bear

    Pooh Bear Guest

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

  9. 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

    I will look into the RF screening. Thanks bunches!

  10. Juno

    Juno Guest

    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!

  11. Phil Allison

    Phil Allison Guest


    ** 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
  12. 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!


  13. Rich Grise

    Rich Grise Guest

    Or just give the ushers long sticks....

  14. Rich Grise

    Rich Grise Guest

    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!
  15. Fred Abse

    Fred Abse Guest

    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.
  16. Get a Grip

    Get a Grip Guest

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

    kell Guest­ducts.aspx?catID=326­ex..htm­cellphonejammer.htm­cell phone jammers.htm



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  18. Jasen Betts

    Jasen Betts Guest

    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.


  19. 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.

  20. 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. ;-)
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