I’m sure it’s not just me because this has been true for as long as I’ve owned cell phones. What gives? Is it the large metal box of the elevator? If it were, I’d think that as soon as the doors closed, I’d lose the signal. What usually happens is that I get about half way up or down and then the call drops.
Any theories?
I find on my phone that the number of bars indicating signal strength takes a few seconds to change after the actual signal changes. I’ve tested this with a Faraday cage. So your signal is likely reduced as soon as the doors close. Additionally as the elevator moves out becomes fully enclosed in a masonry or concrete shaft which further reduces your signal.
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Note a Faraday cage is a metal enclosure. Put your cell phone inside a metal tool box and call it. See if it gets the signal and rings.
An elevator is a metal enclosure or Faraday cage.
Faraday cage…
I have often been able to sustain a call while in a moving elevator. Driving into an underground parking garage, however, is usually a call-killer.
the elevator is a metal box inside a building, which is presumably built out of steel and concrete. the amount of RF energy that can get into or out of the elevator is going to be further attenuated by the building itself.
your car is also a metal box, but it has large glass openings through which to let signal pass.
It’s all about the mass of material around you blocking your signal. When you are in a car, you have a relatively thin shell around you. In an elevator, the “box” of the elevator, the shaft itself, and the mass of the building is around you.
This is just a SWAG, but here’s my explanation for why the call doesn’t drop until a short time after the elevator door closes:
Once the door closes, your signal reception unsurprisingly drops way down. To compensate, the phone cranks up the gain on its low noise amplifier to try to improve reception. Soon, the gain is maxed out but the signal quality is still insufficient to maintain the call, so the call drops.
Another potential factor is that reception may vary depending on where you are in the elevator shaft. The phone might be able to barely maintain a connection, until you pass a floor where the building architecture or furniture layout pushes you below the threshold.
no, it’s about wavelengths. You can make a Faraday cage out of fine mesh screen, so long as the openings in the screen are smaller than the wavelength of signal you want to block (about 1/10th the wavelength.)
An elevator is not really a complete enclosure. If you actually saw an elevator disassembled outside the shaft, you’d see that there are a number of openings through which the microwave frequency transmission (S-band and L-band frequency spectrums spanning 1–4 GHz, or about 7.5 to 30 cm wavelength). Although the signal will be degraded, it can enter and leave the box. An automobile is a terribly shield against microwave transmissions because it has giant cavities that are transparent to EM radiation, including all radio and most visible light; yes, I mean windows.
A true Faraday cage is a continuous fine mesh or solid foil which is full ensconced with no apertures. These are used to protect against static and quasi-static electromagnetic radiation (e.g. a shielded coaxial cable) but can still be affected by highly transient fields which will create variable inductance in the shield, and are permeable to magnetic fields.
You can’t transmit from an underground garage not because it is a Faraday cage, but because the sheer amount of mass of dirt and concrete (as well as interference from steel reinforcement) simply absorbs the radiation to the point that it is attenuated to nothing.
Stranger
An elevator travels through a thick steel and concrete shaft with openings where the doors are. When you are most completely surrounded by concrete walls is when the signal is worst. It gets better when you reach a floor but if you don’t get off on that floor your phone doesn’t get enough time to reestablish the link. (The preceding was all WAG)
Although as an elevator moves there are going to be times where LOS is trying to penetrate slabs of concrete and rebar floor horizontally, which aint gonna happen. Im sure plenty of buildings have dead zones due to such tower/structure positioning problems.
Does lead work of the “F” cage?
Good!
The rest of us don’t want to listen to your inane chatter while we are trapped in that elevator with you. What is there about owning a cell phone that causes some people to forget all manners?
I’ll just point out that cellular phones require a signal for many functions other than talking. Forum rules do not permit me to comment further.