On Mon, 18 Oct 2004 00:57:07 -0500, clifto wrote:

Tony Calguire wrote:
What exactly are these search and rescue people listening for? Wouldn't
an emergency beacon be sending some kind of intelligent signal, like SOS
in morse code, or some kind of RTTY? At the very least, a certain kind
of modulated tone. It seems to me that if they're going to chase after
every spurious signal that pops up on 121.5, no matter what it sounds
like, that's a recipe for failure. No wonder 90% of their hits are
false positives.

If you find yourself in a heap of burning airplane parts in some valley
one day, I really hope they're still looking for weak signals on that
frequency if your ELT gets damaged. You'll hope so, too.
that's one of the reasons 121.5 Mhz ELT's are going away. They are
simply beacons, and any signal on 121.5 can be an ELT,maximum power
out is 100mw. The EPIRB and PLB use a digitally encoded 406Mhz signal
with a 5 watt output, and contains the beacon ID, and can also carry a
GPS determined position as a data payload. In addition all 406Mhz
units must be registered, because 121.5 and 243 Mhz units are not
encoded, they are not registered.