Current bugbears

[John Seghers]

Alexey Feldgendler wrote:

> Except GPS, I guess. Because GPS is just a receiver, it cannot add any  
> interference and hence doesn't need to be disabled. Actually, GPS could  
> provide some fun in a flight.

NO. Including GPS.  Every flight I've been on recently has state that
electronic devices which send *or* receive signals are not allowed (or those
capabilities switched off.)

Part of the process of receiving signals involves heterodyning--basically
mixing a received signal with lower intermediate frequencies (IFs) to
amplify the desired actual signal, while making the carrier signal something
easier to work with. See http://en.wikipedia.org/wiki/Heterodyne for a very
basic description.

Any oscillator will radiate some electromagnetic interference. Furthermore,
because the intermediate frequencies are often similar (or in the case of
GPS identical) to other such devices, those stages can interfere with each
other.

For another example, in states where radar detectors are illegal, the police
can use sensors tuned to the first stage IF (around 900MHz IIRC) of the
radar receiver to find cars that have them onboard.
(http://radar.757.org/VG2.htm)

As the onboard electronics in aircraft are upgraded to those designed in an
age of digital electronics, Bluetooth, GPS, cell phones, etc, these
restrictions will probably fall by the wayside.

However, today the regulatory agencies have to look at the least capable
machinery flying out there when they make the rules.  Most airlines also
tend to over-generalize things simply because it makes it easier to
communicate what is allowed and what isn't.

- John