Turn off your phone!

By Patrick Carrier

Everybody knows you are supposed to turn off your phone and other electronic devices when you are on a plane.  You can leave it on during the flight, but it has to be off for takeoff and landing.  I like to remind people in case they “forget”.  I tend not to make a big deal during takeoff, but landing has me a little more on edge.

The problem is coupled noise.  Sure, most modern planes should be designed such that some electronic interference in the cabin should not affect the plane’s electronics, but you never know.  And is it worth the risk?  I don’t think so.  The thing that worries me most is the fact that many handheld electronics take some design shortcuts in order to minimize cost.  Where many should probably use boards with 4 or more layers, often they will only use two layers.  That means that the PCB traces, instead of coupling noise onto a solid plane (no pun intended (seriously, I meant an actual ground plane (no, not a grounded plane (although that could be the result) but an actual solid sheet of copper in the PCB (which yes, should of course be grounded, anyway, I digress….)))), are coupling noise out into the world.  Such coupling is a special kind of “crosstalk” commonly referred to as electromagnetic interference, or EMI.  It is but one of the many mechanisms that unwanted noise can get coupled from one place to another in electronic designs.  You can read more about noise coupling in the following article:

And please, turn off your phone when you are on a plane (more precisely, an airplane) during takeoff and landing.  Unless you can see the radiated emissions (which you can’t, even if you squint) you won’t know they are there.

And speaking of radiated emissions… well, no, that’s really the subject for another blog.  It has to do with restricting airport restaurants from serving beans…

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This article first appeared on the Siemens Digital Industries Software blog at