No signal in a metal clad building

[turretslug]

There's also the famous demo of putting a mobile phone in a micro-wave oven, closing the door and being able to ring it- I think it merely shows just how robust digital reception and error-correction can be!

[petertheorgan]

I was going to make the comment that when I am on holiday, I leave my mobile phone in the room safe at my holiday complex . This is effectively a solid metal box , but the phone still picks up calls and txt messages when locked inside and I have often wondered how the signal gets in to the box?

I shall be interested in an explanation.

Peter/

[Herald1360]

The safe and its door are probably painted and don't make good contact with each other all the way round. Any cracks longer than about a tenth of a wavelength will let RF in. If you seam welded the door to the box it would probably keep the signal out

Good (100dB plus) RF screened rooms are seriously expensive for good reasons!

[Biggles]

When mobile phones were relatively new and still a novelty, we put one inside a metal biscuit tin at work and closed the lid and it still rang much to our surprise. The lid was a very tight fit and electrically connected. I suppose there must have just been enough leakage for it to work, or maybe some sort of capacitive coupling to the outside world.

[Skywave]

Many quality signal generators which use valves have double screening around many parts - especially the prime freq. generating cctry. and the O/P attenuator. Classic Marconi sig. gens. are often found with this arrangement. F.E. Terman discusses such arrangements and the need for such screening in his book 'Electronic and Radio Engineering', 4th. ed.

Al.

[G8HQP Dave]

Originally Posted by Biggles

The lid was a very tight fit and electrically connected.

The lid would only have made good electrical contact at a few places. Elsewhere it would have provided a narrow slot with a bit of capacitance across it. Not a significant barrier to UHF and microwaves; slots are used as antennas! Once inside the box the RF energy would see the phone antenna as the main absorber, as everything else is reflective metal.