Loop to 'block' mobile phone signals

spurious

I hope this is the correct forum.

Has anyone here heard of a system which is essentially made up of a loop around a building which renders mobile phones within the loop unusable (since they can't get a signal - possibly because of a magnetic field)?

My Leaving Cert. Physics is rather rusty at this stage, but in theory would this be possible? Anyone any opinions?

Spear

spurious wrote: »

I hope this is the correct forum.

Has anyone here heard of a system which is essentially made up of a loop around a building which renders mobile phones within the loop unusable (since they can't get a signal - possibly because of a magnetic field)?

My Leaving Cert. Physics is rather rusty at this stage, but in theory would this be possible? Anyone any opinions?

You mean something like a Faraday cage?

spurious

In principle, yes. Something that could be switched on and off.

I'm thinking along the lines of a system that would stop mobiles from getting a signal in one section of a building, while allowing access in the rest of it. I could see lots of applications for it, unless prohibitively expensive.

Actually rooting about it seems it would be very expensive - dangnabbit - back to the drawing board. Thanks for your help.

Michael Collins

Physically blocking mobile phone signals would be very difficult since your phone is an extremely sensitive device that can work even when the signal is extremely attenuated. Try putting your phone in the microwave oven (don't turn it on!) and see if you can ring it. It will more than likely work fine, since the microwave, although designed to block microwave signals (that your phone uses to communicate with the base station), will still let a small percentage of the energy though it. A microwave oven is a small device that is almost completely covered in metal an even it doesn't work - trying to block a whole building from getting phone signals would be extremely difficult.

However, there is a solution! Instead of blocking the signal - jam it! Emit a signal very similar to what the phone uses to communicate, but much stronger. The phone won't be able to use the weak comm. signal from the base station in the presence of the strong interfering carrier...

ga2re2t

I thought certain cinemas had phone jamming technology ...?

Michael Collins

Yep, heard that myself. Not sure if there's any in Ireland yet, or at least Dublin anyway.

fishdog

I thought certain cinemas had phone jamming technology ...?

I heard this also.

I guess that if it was easy to do they would have this system in all of the prisons!

Shrapnel

fishdog wrote: »

I heard this also.

I guess that if it was easy to do they would have this system in all of the prisons!

It's not a lack of technology that prevents the mobiles in prisons being blocked.
But that's going off topic.