CELL JAMMER

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jimandy
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Re: CELL JAMMER

Post by jimandy » Fri Mar 25, 2005 4:30 pm

At the risk of flogging a dead horse...I keep harping on the need for a system to detect the presence of the cell phone. Then you can do what you want when you know one is present.<p>Now I find a source for a detector<p>http://www.antennasystems.com/cellular/ ... ector.html<p>Do you think this thing really works?
"if it's not another it's one thing."

bridgen
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Re: CELL JAMMER

Post by bridgen » Fri Mar 25, 2005 5:00 pm

I doubt for one moment that it works.
It won't be cheap though.

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sofaspud
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Re: CELL JAMMER

Post by sofaspud » Fri Mar 25, 2005 6:23 pm

Not too long ago TJ Byers had a simple cellphone detector in his N&V Q&A column. It was for close-range detection, but could an amplifier be added to the frontend to increase the range? Anyone else remember this?

terri
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Re: CELL JAMMER

Post by terri » Fri Mar 25, 2005 9:55 pm

Hmmm... I wonder if trying to put a Faraday cage around the store is even remotely practical. In my building (downtown Denver CO) the cell phones seem to work even in the elevators... but of course, the building may be close to cell phone transmitters. Seems to me that teeny little one-foot signal can sneak through all kinds of teeny little openings.<p>Personally, I'd rather see jammers along the highways and byways of the nation.<p>Well, I've been accused of being both too practical, and at the next turn, being too impractical --the above perhaps exhibits both personal characteristics.<p>Most likely reason to want to prevent cell phone use is 'cause the proprietor doesn't want unauthorized transmission of pix from the store. There are a couple of possibilities for the reason why, but I'll let you guess.<p>[ March 26, 2005: Message edited by: terri ]</p>
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jimandy
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Re: CELL JAMMER

Post by jimandy » Sat Mar 26, 2005 9:02 am

What amazes me is what some people will say on a cell phone in a public place. I sat near a lady in a cafe who carried on a conversation in which she was applying for a home equity loan. The information she related included her home address, income sources and amounts, net worth, and social security number.<p>When she was through I went over and asked her if she would marry me.
;)
"if it's not another it's one thing."

terri
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Re: CELL JAMMER

Post by terri » Sat Mar 26, 2005 9:19 am

Gigolo!
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Bob Haller
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Re: CELL JAMMER

Post by Bob Haller » Sat Mar 26, 2005 2:20 pm

If I found out a store was jamming my cell they wouldnt have to worry about me on my cell, I would NEVER shop there again....<p>I vote with my feet :)

terri
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Re: CELL JAMMER

Post by terri » Sat Mar 26, 2005 4:21 pm

Well, jamming is one thing, since it's illegal. But for just one scenario where a store proprietor might not want possible cell phone picture transmissions, is where it is an art gallery.<p>Another might be a lingerie store.<p>A couple of other possibilites occur to me which border on the racy and even exxy --but that'sthe way my pervy little mind works.<p>And, while you might not go taking pictures and transmitting them to your home hard drive and putting them on the 'net, there are definitely others who would, despite the violations of copyright laws in the case of the art gallery, and violating the privacy rights of the models --among other things.<p>These are just a couple of places where the store owner might not want cell phones transmitting stuff from his establishment --and quite legitimately so.<p>Anyhow, getting back to Schwarz's problem, probably a detector such as noted in the site mentioned above would work best. <p>The store owner could probably easily figure out who's using the cell phone and diplomatically advise the customer that if he needed to make a call, the store has a hard-wired phone they would be welcome to use --but that cell phones, especially ones with cameras, can't be used in the store.<p>That seems to me to be the best solution without ruffling customers' feathers too much, without "Faraday-caging" the place (which probably wouldn't work), and without breaking the law with a jammer.<p>Make sense?<p>[ March 29, 2005: Message edited by: terri ]</p>
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Bernius1
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Re: CELL JAMMER

Post by Bernius1 » Mon Mar 28, 2005 1:43 pm

AM radios (& sometimes computers )pick up the broadcasted packets from a cellphone as a 'chick-chick-chick' sounding distortion. But I don't get it so much from the 1.4GHz+ phones , as from the older 800MHz-900MHz phones. Either way, it's an AM modulation, so a receiver looking for those clicks needs only to trigger a recording "We remind our patrons that cell phone use is prohibited in this establishment." Since cell phones are FM modulated in known freq. bands, the ckt can't be TOO difficult, the calls will still be secure, and it's a receiver, so there's no chance of Friends Coming Close to investigate.
Can't we end all posts with a comical quip?

angat
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Re: CELL JAMMER

Post by angat » Fri Apr 01, 2005 11:59 pm

Hello All
We Angat Tech Is Selling GSM Jammer(Mobile Jammer) In India. so any further query mail me<p>Thanming you,
Om
(Chief R&D Department)
Jaydeep Thakkar

rshayes
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Re: CELL JAMMER

Post by rshayes » Sat Apr 02, 2005 12:48 am

Unless the store is large, it seems that it might be possible to put a detector within about 25 feet of any point in the store. The signal at this point may be strong enough to be received by a very simple receiver. If the cell phone is transmitting to an antenna 2500 feet away, the signal within the store would be 10,000 times stronger than the signal at the remote antenna. This is quite an advantage.<p>The signal might be strong enough to be picked up by a very simple receiver, possibly a half-wave antenna and a diode detector. The detector could be connected directly to the antenna, to avoid transmission lines. The detector output woul be millivolts at best, but a couple of stages of amplification could bring this up to a reasonable level. The output could be shielded wire or coax, and DC power could be brought in on the same cable for the amplifier.<p>You would probably need a receiver for each potential transmission band. It appears that four bands are in use, and they seem to be fairly narrow, which simplifies the antenna design.<p>I suspect that a cell phone has to send a short burst of signal (probably less than a millisecond long) at fairly frequent intervals, possibly every few seconds to a minute or two. Otherwise, the cellular phone system would have no way of detecting that the phone had moved between cells. These short bursts, if they exist, are probably quite distinctive.<p>The content of radio communications, except for broadcasts, are private, and cannot be divulged or used by parties intercepting them. I don't know if detecting the fact of the commmunication without knowing the contents falls under the same rules. You might need a lawyer for that question.

Adam Y.
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Re: CELL JAMMER

Post by Adam Y. » Sat Apr 02, 2005 10:00 am

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>And, while you might not go taking pictures and transmitting them to your home hard drive and putting them on the 'net, there are definitely others who would, despite the violations of copyright laws in the case of the art gallery, and violating the privacy rights of the models --among other things. <hr></blockquote>
Ummmmm... So they take the pictures and then go outside to send them home. It really doesn't stop anything.

terri
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Re: CELL JAMMER

Post by terri » Sat Apr 02, 2005 1:45 pm

Hm. Good point. Maybe it doesn't make that much sense, after all. How many pics can you take on a cell phone before sending them?
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opamp
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Re: CELL JAMMER

Post by opamp » Sat Apr 02, 2005 9:35 pm

Gosh, I would hate to be an on-call Emergency-room doctor going to a movie in one of those 'Cell Phone Protected' theaters.

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