3 ms·

You raise a good technical point, once which I don't have the E&M background to comment on. But, I think there is an obvious question: if it's relatively easy t

by scott_s 14y ago

You raise a good technical point, once which I don't have the E&M background to comment on. But, I think there is an obvious question: if it's relatively easy to setup these circumstances where interference from many devices can effect the instruments in a modern plane, why don't we have such demonstrations? The FAA's position is that they don't have proof that the devices are completely safe to use. But what experiments have they carried out? If they had experiments which showed that the devices are not safe to use, I would assume they would just cite those. If they don't have any experiments, then I find that troubling as well. If they do have experiments, then how many do we have to perform before we realize that you can't prove a negative? (That is, if the devices are safe, you can't experimentally prove this.)

wglb 14y ago
The trick is that the experiment might get back a "sometimes" result. That is, sometimes a certain combination of devices causes a radio spur to give one of the avionics a little tickle. Then, if something drifts (as CPU clocks will) the spur goes away, or drifts off to a harmless band, or onto something else you are not watching. And doing the test on the ground is not convincing, as the signals the instruments are looking at are at a larger strength than the spurs. How does the spur compete with the ever-weakening signal as the plane flies further out? The desired signal declines as the square of the distance, where as the junk in the passenger compartment is not changing. And you can also do the math on this, and it is intimidating. The math says to take the sum and difference of every pair of radio signals to see the full spectrum of hash put out by the collection of devices. With three or five radios (I am including the unintentional transmitters here as well, like CPU clocks) on 200 devices, that is how many pairs? Now, how many signals does that spit out? And if they did site such a study, the social pressure would still be here. In the article, we are referencing the acumen of Alec Baldwin and Claire McCaskell. (Spur is jargon for Spurious Signal.) The military faced a problem in the same space but of a different magnitude. Powerful radars need to be turned off during takeoff and landing for some aircraft so they are not blind.

by scott_s 14y ago

wglb 14y ago

The trick is that the experiment might get back a "sometimes" result. That is, sometimes a certain combination of devices causes a radio spur to give one of the avionics a little tickle. Then, if something drifts (as CPU clocks will) the spur goes away, or drifts off to a harmless band, or onto something else you are not watching. And doing the test on the ground is not convincing, as the signals the instruments are looking at are at a larger strength than the spurs. How does the spur compete with the ever-weakening signal as the plane flies further out? The desired signal declines as the square of the distance, where as the junk in the passenger compartment is not changing. And you can also do the math on this, and it is intimidating. The math says to take the sum and difference of every pair of radio signals to see the full spectrum of hash put out by the collection of devices. With three or five radios (I am including the unintentional transmitters here as well, like CPU clocks) on 200 devices, that is how many pairs? Now, how many signals does that spit out? And if they did site such a study, the social pressure would still be here. In the article, we are referencing the acumen of Alec Baldwin and Claire McCaskell. (Spur is jargon for Spurious Signal.) The military faced a problem in the same space but of a different magnitude. Powerful radars need to be turned off during takeoff and landing for some aircraft so they are not blind.