[geeks] GPS on planes

[Geoffrey S. Mendelson]

The problem with using GPS on an airplane is that the pilots also use
GPS. Your handheld receiver is very likely to prevent theirs from working.
How?

<technical explanation>
All GPS receivers are of the superhetrodyne type. That means that (using
round numbers), let's say the GPS sattelites transmit at 11.123 gHz.
Some receivers will use an oscilator (radio signal generator) at 10.000 gHz,
mix it with the GPS signal and produce a new signal at 1.123 gHz.

Depending upon how well sheilded your receiver is from "leaking" signal,
it could interfere with the airplanes GPS receiver. The leaking signal
since it would be so close would not only cover the GPS signal from the
sattelite, but it would prevent the recevier from hearing it at all.

Strong signals not only "capture" a receiver, put they desesitise the 
front end. The signals don't have to be close in frequencey, just near,
and at those frequencies, it's near enough.

Now imagine if the receiver used a local oscilator frequency of 11.000 gHz.
The local oscilator would not only interfere with their GPS, but with a
product of .123 gHz, the mixed signal at 123mHz, right in the middle of
the aircraft band, interfeering with their short range ground communications.
</technical explanation>

Geoff.
-- 
Geoffrey S. Mendelson gsm at mendelson.com 972-54-608-069
Do sysadmins count networked sheep?