In article ,
Tony Calguire wrote:
postal97321 wrote:
....
Ryan Gardner/Gazette-Times
Chris van Rossman's television sent out a distress signal that was
picked up by an orbiting satellite.
....

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.

It's some sort of a warble tone on a carrier.

They use a transponder on polar orbiting satellites (weather and earth
sensing ones, usually) that allows the ground stations to do a doppler
measurement. Sort of the reverse of the Transit satellite navigation
system, where the timing and frequency shift of the signal allowed the
ground station to determine its position to a fraction of the meter.
The Transit system used atomic clocks, so the SARSAT accuracy would be
lower. But accurate enough to get the search and rescue close enough to
use portable direction finding gear.

Mark Zenier Washington State resident