DX Cell Phone Blockers

[ZRTMWA]

Has anyone bought or used one of the DX Cell Phone Blockers? I know they are illegal in the US but I think DX still ships them here. They seem pretty crappy but maybe they can be tweaked to use at longer distances. I might just try to but one since they are under $30. Thanks.

http://www.dealextreme.com/products.dx/category.405~search.cell phone blocker

 

[Tech_Junkie]

I know they are illegal in the US

That's because they use them to block back up cellular burglar alarms.

 

[john_lawson]

they suck my friend tried 2 different models you have to be within 5 foot

 

[Tech_Junkie]

What else would you use these for Johny?

 

[pseudolobster]

My boss bought three of them... Whatever you do, don't buy this one: DealExtreme: $61.74 36W High Powered Cell Phone Blocker/Jammer (3G/GMS/CDMA/DCS/PHS) ... Out of the three, this one was the worst, it only blocks one local CDMA carrier, and only within a foot or two. GSM phones are unaffected.

The other two he bought look like this: DealExtreme: $27.08 Personal Cell Phone Signal Blocker Device ... I'm not sure exactly which two skus they are though... They work fairly well, blocking a range of ten to twenty feet or so, and when you put the antennas from sku 11510 on them, they get a decent 30 feet or so.

An ironic thing about these is that some people buy them to "protect themselves from radio waves", yet the way these things work is by transmitting radio waves with higher intensity than the cell phones in the area, blocking them out.. The phones respond to this by turning their own antennas to the max, sending out much higher levels of radio waves than normal, trying to get a connection... So, if you're buying one of these to replace your tinfoil hat, remember this won't remove radio waves, instead it'll amplify them ten fold.

 

[Flaminpyro]

@ pseudo my tin foil hat is realy made from Zirconium foil will that be enough to block the extra signal strength LOL :tinfoil::tinfoil::tinfoil:

My boss bought three of them... Whatever you do, don't buy this one: DealExtreme: $61.74 36W High Powered Cell Phone Blocker/Jammer (3G/GMS/CDMA/DCS/PHS) ... Out of the three, this one was the worst, it only blocks one local CDMA carrier, and only within a foot or two. GSM phones are unaffected.

The other two he bought look like this: DealExtreme: $27.08 Personal Cell Phone Signal Blocker Device ... I'm not sure exactly which two skus they are though... They work fairly well, blocking a range of ten to twenty feet or so, and when you put the antennas from sku 11510 on them, they get a decent 30 feet or so.

An ironic thing about these is that some people buy them to "protect themselves from radio waves", yet the way these things work is by transmitting radio waves with higher intensity than the cell phones in the area, blocking them out.. The phones respond to this by turning their own antennas to the max, sending out much higher levels of radio waves than normal, trying to get a connection... So, if you're buying one of these to replace your tinfoil hat, remember this won't remove radio waves, instead it'll amplify them ten fold.

 

[HIMNL9]

Well, after all, they are not sold as "long range phone blockers", just as privacy tools.

Like, when you're in a place where you want to be relaxed (maybe in sweet company ), and still hear cellphones ringing all around you each 10 seconds, you can use one of these for have a little zone of silence (another use can be for block any audio-bugs or gsm trackers that someone may have hidden in your car or room, as example).

But don't hope that, with these low power units, you can cover high distances or big areas.

The ones that they sell for large areas, here (other than require a valid reason and a police authorization ..... as example, one of our churches obtained an authorization for use one of them inside the church, only in the functions times), have external antennas, and prices that start from 700 euro and grow up very quick

 

[ZRTMWA]

... So, if you're buying one of these to replace your tinfoil hat, remember this won't remove radio waves, instead it'll amplify them ten fold.

Well that ruins my plans. Just kidding. So one semi positive review (psuedolobster) and one negative review (j_l). This seems about the same as on the DX sites reviews, (3 stars). Must be really hit or miss.

I thought these were illegal in the US because they could block a call of someone who was trying to call an ambulance, the polie or the fire department. Or is that what you were saying T_J?

I found this instructables on how to increase the range of those crappy little ones:

Adjusting the caps

Think it would work?

 

[Elektrotechniker]

Excuse me but what is a phone blocker?

 

[pseudolobster]

[...]
I thought these were illegal in the US because they could block a call of someone who was trying to call an ambulance, the polie or the fire department. Or is that what you were saying T_J?
[...]

They're illegal because you're willfully interfering with licensed broadcasting devices. If you block out a radio station you're interfering with the radio station's licensed right to broadcast on that frequency. They paid money to be able to broadcast on that station, so you're not allowed to deprive them of their licensed transmission.
People always use 911 calls as an example that everyone can understand and relate to, but really you're simply not allowed to broadcast on those frequencies without a license.
FCC: Wireless Services: Cellular Services: Operations: Blocking & Jamming

Yes, you can tune these devices to choose what band they block, though it doesn't increase the power, it just changes the frequency. Without some sort of antenna tuner or whatnot, you're going to be changing the frequency blindly, so you might end up making it worse.

 

[ZRTMWA]

Excuse me but what is a phone blocker?

It basically makes you have 0 bars. If you're on your cell phone when a jammer is activated near you the call will be dropped. That is the layman's definition. Psuedolobster explained it farther up.

 

[HIMNL9]

^ BTW, those "small capacitors" are trimmer (pots),

From the pics, it look as a multiple frequency generator (maybe PLL ?) with 3 independent RF amplifiers ..... i think that, apart tuning the frequencies to your country ones, the only effective ways for increase a bit (but just a bit) the range, are

1) using high gain tuned antennas, but this take away the "hidden portability" (not so easy to go around keeping it hidden, with 40 / 50 cm of antennas coming out from your pocket ) ..... but for fixed installation, is probably the best choice (and in case of fixed installations, also using cables and take the antennas far half meter or so one from the other can help).

2) mess up a bit with the RF amplifiers, but careful, without all the datasheets and trying this blindly, you risk to "smoke out" the entire unit (POOF, and then no more jammer )

 

[Benm]

How effective these things are depends on a number of factors. Provided they are tuned for the proper frequency, there is still the signal strength from the cellphone tower and/or handset to overcome.

The problem is that these jammers need to cover the whole band, as the phone/tower link will otherwise just switch to a channel that is not effective. As there are 125 channels, it would have to be in the order of 125 times stronger in output than the phone to disrupt the uplink. GSM phones have 1 or 2 watt max power output, so this is more or less a no go.

What can be distrubed is the singal from the tower to the handset. The effective range of a jammer gets bigger the further away from the cell tower you are - which may make the same jammer work 'very well for 100 feet' in a rural area, and 'only for 2 feet' in an urban environment.

They can be used most times to jam cell signals in a small room or office, perhaps useful to avoid listing devices that work on the gsm network.

Using them is illegal in most countries though, and can also have serious consequences. You have little control over the effective range, and it could, for example, also jam someone calling for an ambulance on the sidewalk in front of your property.

 

[Tech_Junkie]

Hi,guy!

Spam.

 

[flecom]

They're illegal because you're willfully interfering with licensed broadcasting devices. If you block out a radio station you're interfering with the radio station's licensed right to broadcast on that frequency. They paid money to be able to broadcast on that station, so you're not allowed to deprive them of their licensed transmission.
People always use 911 calls as an example that everyone can understand and relate to, but really you're simply not allowed to broadcast on those frequencies without a license.
FCC: Wireless Services: Cellular Services: Operations: Blocking & Jamming

Yes, you can tune these devices to choose what band they block, though it doesn't increase the power, it just changes the frequency. Without some sort of antenna tuner or whatnot, you're going to be changing the frequency blindly, so you might end up making it worse.

correct, unlawful interference, plus you are now transmitting on bands/frequencies that you are not licensed for...

these are very much illegal and if you do get a NAL from the FCC there is usually a pretty substantial fine attached to it

 

[HaloBlu]

Well now that this thread is back from the dead..
Anyone have experience with GPS jammers?

If anyone else has any interest in jammer design I found Ladyada's Wavebubble quite interesting, too bad the cost of parts isn't less.

Jamming seems so inefficient & inelegant to me. Blocking use can be so much easier on wifi.
There was a recent demonstration of a DIY cell tower spoofer costing only $1500 & most of that was the laptop they say.