On Jun 22, 3:41*am, Scott wrote:
brian whatcott wrote:
Since satellite cover has been withdrawn for 121.5
(High false alert rate, poor localization)
406.0 and 406.1 ELTs will be needed, following a recent FCC determination.

Brian W

I can see the 406 units providing better localization, but how do they
lower the high false alert rate? *I assume they still use a "G Switch"
to activate?

I would think that localization could be good on the 121.5 units if they
would be made to accept GPS data and transmit lat/long data when they go
off...

The 406 MHZ ELT or PLB may not have a GPS or may not be ale to get a
GPS fix, the position of the device is then determined by doppler
triangulation from the orbiting (non-geostationary) COASPAS-SARSAT
satellites. The higher frequency and higher spectral purity specs of
the 406 MHz transmitters enable better Doppler triangulation. A
relatively accurate Doppler fix takes several passes of these
satellites. The reception of the alert and the unique ELT or PLB
digital ID is immediate (via geostationary satellites). You get all
this by throwing away the crappy old 121.5 Mhz ELTs and replacing them
with a modern device.

If a 406 MHz PLB or ELT has a GPS unit (many low-cost PLBs do now)
then it transmits its GPS position if it has a fix and that is
immediately received by the geostationary COSPAS-SARASAT satellites.

The old 121.5Mhz devices are analog, 406 Mhz has many advantages over
121.5 MHz. The solution is to throw out the old junk and move to 406
MHz. 121.5MHz PLBs belong in a landfill, and the FCC is on the right
path here.

Darryl