# Tell me ALMOST all about cell phone jammers **URL:** \ **Category:** Factual Questions\ **Created:** [January 26, 2007, 5:44pm UTC](https://boards.straightdope.com/t/tell-me-almost-all-about-cell-phone-jammers/389588 "2007-01-26T17:44:30Z")\ **Posts on this page:** 10\ **Page:** 3
**Author:** ![yabob](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yabob/32/2821_2.png) [@yabob](https://boards.straightdope.com/u/yabob)\ **Post date:** [January 28, 2007, 4:23pm UTC](https://boards.straightdope.com/t/tell-me-almost-all-about-cell-phone-jammers/389588/41 "2007-01-28T16:23:39Z")
Re “Faraday Caging” buildings: Several years back, the subject of jammers was being kicked about on the local talk radio station. They had a caller who said he was a contractor who RF shielded buildings, and that it was both effective and legal. He also said that it probably wasn’t going to be a reasonable solution for a restaurant owner because it was expensive - most of his customers were medical clinics, who are very anal about RF around their equipment (probably with justification). ---
**Author:** ![gazpacho](https://avatars.discourse-cdn.com/v4/letter/g/6f9a4e/32.png) [@gazpacho](https://boards.straightdope.com/u/gazpacho)\ **Post date:** [January 28, 2007, 4:58pm UTC](https://boards.straightdope.com/t/tell-me-almost-all-about-cell-phone-jammers/389588/42 "2007-01-28T16:58:46Z")
[QUOTE=Merijeek] So, what would it take (power-wise and equipment-wise) to jam ALL frequencies in the given area? Is this something that could be fit in a briefcase? A car? A semi trailer? Would it take an entire building? -Joe [/QUOTE] I would take on the order of 5 to 200 watts but that is a very wild ass guess. There are a lot of channels that can be used by cell phones so the transmitter would have to transmit at a fairly broad band of frequencies to guarantee disrupting service for all phones. This is a brief case sort of thing maybe a very heavy brief case if you need to run off grid for a while. As technology moves along it gets harder to jam cell phones because keeping phones from being jammed is a very similar problem to increasing the number of calls that be handled in one area. ---
**Author:** ![thirdname](https://avatars.discourse-cdn.com/v4/letter/t/d07c76/32.png) [@thirdname](https://boards.straightdope.com/u/thirdname)\ **Post date:** [February 11, 2007, 1:55am UTC](https://boards.straightdope.com/t/tell-me-almost-all-about-cell-phone-jammers/389588/43 "2007-02-11T01:55:29Z")
[QUOTE=xiix] If Carl got pulled over and felt an alteration was inevitable [/QUOTE] Indeed, cops in my area are so dangerous they’ll hem your pants just for looking at them funny. ---
**Author:** ![Rico](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rico/32/3582_2.png) [@Rico](https://boards.straightdope.com/u/Rico)\ **Post date:** [February 11, 2007, 2:27am UTC](https://boards.straightdope.com/t/tell-me-almost-all-about-cell-phone-jammers/389588/44 "2007-02-11T02:27:23Z")
[QUOTE=St. Urho] My understanding is that frequency hopping changes the frequency during the broadcast, while with trunking, the entire broadcast is done on the same frequency. [/QUOTE] No. [Trunking](http://scanct.com/trunking/#1) can be likened to a telephone system. Think of it this way. Picture a town with 1000 residents. Without a trunking telephone system, each resident would have his own dedicated trunk line to the system. So you would need 1000 trunk lines to the outside system to feed this non-trunking configuration. Put a trunking system in place, and you can drop the number of trunk lines down to 15-20! That’s because not everyone is using their phone at the same time and we can conserve our outside line costs by switching each phone to an available outside line (or _trunking_ it). If all lines are busy when John Somebody picks up his phone, he will not get a dial tone until someone releases a line, at which point John will be automatically _trunked_ to the outside line. Same with radio trunking systems. In the LTR system, you have up to 20 channels, each user is assigned a “home channel” and a “code”. When User A keys up to call his fleet, a signal is sent out on his home channel (a quick data burst) to the repeater, which sends back either A) a go-ahead to transmit or B) Switch to Channel # and transmit there. In either case, the entire fleet receives the signal and follows the repeater to the channel the base is transmitting on. This takes approximately 0.1 seconds, and is signified to the transmitting party by a “beep” tone after keying his microphone. If all channels are busy, the user receives a busy tone, and tries again. So while a trunking radio does “frequency hop,” quite a bit of the time it is only transmitting on it’s “home channel.” It only frequency hops when that channel is busy. Make sense? ---
**Author:** ![Merijeek](https://avatars.discourse-cdn.com/v4/letter/m/f05b48/32.png) [@Merijeek](https://boards.straightdope.com/u/Merijeek)\ **Post date:** [February 11, 2007, 3:07am UTC](https://boards.straightdope.com/t/tell-me-almost-all-about-cell-phone-jammers/389588/45 "2007-02-11T03:07:04Z")
[QUOTE=gazpacho] I would take on the order of 5 to 200 watts but that is a very wild ass guess. There are a lot of channels that can be used by cell phones so the transmitter would have to transmit at a fairly broad band of frequencies to guarantee disrupting service for all phones. This is a brief case sort of thing maybe a very heavy brief case if you need to run off grid for a while. As technology moves along it gets harder to jam cell phones because keeping phones from being jammed is a very similar problem to increasing the number of calls that be handled in one area. [/QUOTE] Okay, so I’ve got my kickass “take that, cell phone talker 5000”. It’s in my briefcase. How big of a radius am I affecting with my massive batteries pumping out 200 watts of annoyance? Ten feet? A city block? Have I got 747’s falling from the sky? -Joe ---
**Author:** ![Hi\_Neighbor](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hi_neighbor/32/494_2.png) [@Hi\_Neighbor](https://boards.straightdope.com/u/Hi_Neighbor)\ **Post date:** [February 11, 2007, 3:38am UTC](https://boards.straightdope.com/t/tell-me-almost-all-about-cell-phone-jammers/389588/46 "2007-02-11T03:38:17Z")
In which case, our heads will all be under water. ---
**Author:** ![Rico](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rico/32/3582_2.png) [@Rico](https://boards.straightdope.com/u/Rico)\ **Post date:** [February 11, 2007, 5:54am UTC](https://boards.straightdope.com/t/tell-me-almost-all-about-cell-phone-jammers/389588/47 "2007-02-11T05:54:42Z")
[QUOTE=Merijeek] Okay, so I’ve got my kickass “take that, cell phone talker 5000”. It’s in my briefcase. How big of a radius am I affecting with my massive batteries pumping out 200 watts of annoyance? Ten feet? A city block? Have I got 747’s falling from the sky? -Joe [/QUOTE] What have you got? Probably a coffin waiting for you. At that frequency, that close to the antenna, and with 200 watts you’d probably be microwaved very nicely in a couple of minutes. ---
**Author:** ![St.Urho](https://avatars.discourse-cdn.com/v4/letter/s/8e7dd6/32.png) [@St.Urho](https://boards.straightdope.com/u/St.Urho)\ **Post date:** [February 11, 2007, 7:51am UTC](https://boards.straightdope.com/t/tell-me-almost-all-about-cell-phone-jammers/389588/48 "2007-02-11T07:51:13Z")
[QUOTE=Rico] No. [Trunking](http://scanct.com/trunking/#1) can be likened to a telephone system. Think of it this way. Picture a town with 1000 residents. Without a trunking telephone system, each resident would have his own dedicated trunk line to the system. So you would need 1000 trunk lines to the outside system to feed this non-trunking configuration. Put a trunking system in place, and you can drop the number of trunk lines down to 15-20! That’s because not everyone is using their phone at the same time and we can conserve our outside line costs by switching each phone to an available outside line (or _trunking_ it). If all lines are busy when John Somebody picks up his phone, he will not get a dial tone until someone releases a line, at which point John will be automatically _trunked_ to the outside line. Same with radio trunking systems. In the LTR system, you have up to 20 channels, each user is assigned a “home channel” and a “code”. When User A keys up to call his fleet, a signal is sent out on his home channel (a quick data burst) to the repeater, which sends back either A) a go-ahead to transmit or B) Switch to Channel # and transmit there. In either case, the entire fleet receives the signal and follows the repeater to the channel the base is transmitting on. This takes approximately 0.1 seconds, and is signified to the transmitting party by a “beep” tone after keying his microphone. If all channels are busy, the user receives a busy tone, and tries again. So while a trunking radio does “frequency hop,” quite a bit of the time it is only transmitting on it’s “home channel.” It only frequency hops when that channel is busy. Make sense? [/QUOTE] Right, but my point was that it doesn’t frequncy hop _during_ a single transmission. Sorry if that wasn’t clear. ---
**Author:** ![Merijeek](https://avatars.discourse-cdn.com/v4/letter/m/f05b48/32.png) [@Merijeek](https://boards.straightdope.com/u/Merijeek)\ **Post date:** [February 11, 2007, 1:03pm UTC](https://boards.straightdope.com/t/tell-me-almost-all-about-cell-phone-jammers/389588/49 "2007-02-11T13:03:39Z")
[QUOTE=Rico] What have you got? Probably a coffin waiting for you. At that frequency, that close to the antenna, and with 200 watts you’d probably be microwaved very nicely in a couple of minutes. [/QUOTE] Well, I’ll obviously have my arm **way** out from my body! -Joe ---
**Author:** ![FRDE](https://avatars.discourse-cdn.com/v4/letter/f/e68b1a/32.png) [@FRDE](https://boards.straightdope.com/u/FRDE)\ **Post date:** [February 11, 2007, 1:49pm UTC](https://boards.straightdope.com/t/tell-me-almost-all-about-cell-phone-jammers/389588/50 "2007-02-11T13:49:53Z")
[QUOTE=xiix] If Carl got pulled over and felt an **alteration** was inevitable [/QUOTE] Actually ‘alteration’ is a slightly obscure word for castration - as in ‘The Alteration’ - by Kingsley Amis > [@](#): > > The year is 1976 and we are alive in an all-Catholic world. The Reformation never took place because Martin Luther made a deal with Rome and became Pope Martin I. The “alteration” proposed to Hubert Anvil, brilliant 10-year-old boy soprano, is that most feared by all males. Pope John XXIV wishes Hubert to preserve the purity of his voice to glorify the Church on a permanent basis; Hubert wishes to share his talent but he has some disquieting thoughts about Pope John’s proposal. I wonder whether alteration would prevent re-offence - after all you can’t be castrated twice. Or is the idea a load of balls ? [Previous page](https://boards.straightdope.com/t/tell-me-almost-all-about-cell-phone-jammers/389588.md?page=2)