CELL PHONE BLOCK

[frhrwa]

anyone know of a schematic or a unit for sale that will block cellphones at somewhat close range.. 100' or so? something that would disconnect the user and keep them off until they are far enough away?..

[jimmy101]

In general what you describe is illegal in the US. You may not deploy a device that interferes with radio transmissions.

[Externet]

Hi.
There is dozens of those gadgets, some with inflated prices.

---> http://www.phonejammer.com/home.php?cat=249
---> http://www.dealextreme.com/search.dx/se ... e%20jammer

And they do have a reason to exist and applications. Am staying away from legalese.
Digging deep, you may find kits or instructables ---> http://www.ladyada.net/make/wavebubble/index.html
Compact fluorescent light bulbs do interfere with radiocommunications, nobody does anything about.
Operating radio transmitters requiere a license. I know of no cell phone licensed users, and they are extremely powerful tools for crooks of all kinds, but good souls amateur radio operators are still mandated to get a license .

Miguel

[Bob Scott]

In general what you describe is illegal in the US. You may not deploy a device that interferes with radio transmissions.

Well, it is possible for a malfunctioning electronic device, say a "PA amplifier", to "accidentally" interfere with the cell phone bands if it's designed just right...

[haklesup]

To interfere with a cell phone specifically is a technical challenge. You actually need to manipulate cell phone signals and spoof cell phone to connect to your false tower. $250 is a very reasonable price for something like that considering what the full price of a phone made in high volume really cost.

To interfere in the cell phone band non specifically should be easier. You'll probably also knock out other devices like WiFi and cordless landline phones in the process maybe at an even greater range. All you really need is an oscillator in of the right frequency onto which you modulate noise if you want to make a continuous wave transmitter. Still a non trivial circuit. For brief attacks a small spark gap transmitter with a broadband antenna might be enough of a buzz to cause a dropped call.

Keep in mind that designing, building and deploying such a thing could put you in the class of a terrorist operating an EMP wepon in the eyes of law enforcement though but I rather think just a miscreant in the eyes of the FCC.

One more thing. something that works on PCS might not work on CDMA in other words you might zap ATT but Verizon might still be able to "hear me now".

Frankly you're better off making the area unattractive to use phones rather than trying to impinge on their rights.

Well, it is possible for a malfunctioning electronic device, say a "PA amplifier", to "accidentally" interfere with the cell phone bands if it's designed just right...

Like the VHF antenna booster that trashed GPS reception in half moon bay for nearly a year.

[jimmy101]

If you want to keep it legal, and not risk the legal ramifications of broadcasting, or blocking other signals, or interfering with someone's pacemaker ...

A Faraday cage greatly attenuates radio waves. If you have a building with foil faced insulation and that insulation happened to be grounded, then there will be zero cell phone signal inside the building. Or, if the building is clad with aluminum siding and the siding is grounded. Windows and doors etc do allow some RF to enter but it is greatly attenuated.

[Robert Reed]

Hi Jimmy
The flaw in just merely grounding any shielding device is the expense and work involved. At UHF frequencies, even a foot of conductor can generate substantial voltages with RF current flowing through it which in turn regenerate the RF signal as do reflectors and directors in some antenna designs. The RF cages I am familiar with were very expensive installations with MULTIPLE grounding throughout. Add gasketed doors and so on made them very expensive. Most of these cages were used in the test bench room and rarely larger than ten feet square.
I would love to have some small shirt pocket device with a hidden power switch for those annoying restaurant occasions where some jerk at the next table is shouting his conversation to the world.

[jimmy101]

All true, a good faraday cage is a lot of work. But, steel framed buildings are often enough to severely inhibit cell phone signals. A bit of shielding might be enough.

[dacflyer]

i had the chance to play with a cellphone jammer..guy that works for military brought me one, that had a problem with the power switch,,it was a easy fix...and i did play with it for a while.. and boy do idiots get mad when they have no signal..its supposed to have a 1/4 mi range.. i was in the wal-mart...lol
one lady was stomping around cussing etc,, i was about to bust out laughing..and people in traffic..started to drive normally...couldnät text and drive
so i know it worked...he bought it somewhere for over 400.00 they use them for jamming cellphones when in a suspect IUD area over in the sandlot...

[haklesup]

Funny how terrorists never blow up cell towers

[frhrwa]

na.. not trying to use it all the time, was only going to fire it up when the fat "a$$ed" salesman sits next to you in a restaurant and talks on his cell like he's talking to someone across the street.. very irritating.. I guess a cold glass of water down his shirt would do the trick tho..

[dacflyer]

lol.. ya i hate that also...and why do so many use their outside voice on a cell phone ? always hollering as if the other person will hear them better..lol
its a phone dude, not a meggaphone..

[haklesup]

Scene: Evening, on a warm summer night. A romantic restruant, couples sitting in corner booths with spouse/significant others etc. No children in sight.

Antagonist enters: Guy wearing suit sits by himself at a table and begins tapping on his smart phone while muttering. Cell phone rings at max volume with a ring tone about "shawties dancin in the club" Loud salesman begins droning on indefinately about the most boring widgets and office bitching you have ever heard in a stage like voice to be heard above the lovers murmurs.

Enter Hero: frwrwh with a booming and commanding voice speaks up "Excuse me sir, but your rude cell phone etiquette is spoiling the mood of this otherwise quaint little bistro, would you please take that outside with the smokers"

Embarressed and compleatly humiliated Salesman huffs and leaves the room while everyone in the restruant erupts in applause, the waitress then brings you a complementary desert plate and flirts with you. Years later you learn the man rejected all modern conveniences and began living in a cave as a hermit in india.

Then you wake up and realize it was all a dream, thank goodness nobody was naked (well, there was something about that waitress).

Dac, that's why they are not legal. People would play with them like they play with spam software just to try it out.

[dacflyer]

ya true...but some places definatly need them..
i have actually heard that some offices here in europe. ..you must impound your phone in some places.
they have the scramblers for theose that do not submit to the rules..mostly in some board meetings or other big office events etc.
my friend in austria has told me that they do this in the hospital phone free areas. so as not to interfere with hospital equip. Hmmm

[haklesup]

Not suprising europeans would do that. They have a hightened sense of distrust of electromagnetic emissions of any kind. For example many WiFi devices available in the US are illegal to use in France. Some countries have laws protecting claimed sufferers of electrosensitivity (often scoffed at as a mental illness in the US). Europeans are also more used to giving up certain civil liberties in the name of security and harmony for example unmanned speed traps, extensive public place video systems, and liscence plate tracking systems on the highways that can follow you for a very long way automatically in real time and from saved files.

As for the hospital thing. It is commonplace in the US to find a cell phone on the hip of every hospital employee and WiFi access in every room. Just last week I observed a WiFi transmitter mounted on the wall of the X-Ray room. Oddly the lab waiting rooms in this same medical group often have no cell phone signs but I think that is more to make waiting in the waiting room more pleasent when it is crowded, not on account of any equipment or people with pace makers. I don't recall if cell phones were in use in sensitive areas like the OR but they are definately in the ER and regular rooms.