A TALE OF TWO BEACONS
The following is a comparison of 121.5 MHz and 406 MHz emergency beacons:
|
121.5 MHz |
406 MHz |
| LOCATION ACCURACY |
12 miles |
2 miles |
| COVERAGE |
Local |
Global |
| SIGNAL POWER |
0.1 Watt |
5 Watts |
| SIGNAL TYPE |
Analog |
Digital |
| ALERT TIME |
2 Hours |
Instantaneous |
| DOPPLER LOCATION |
Two Passes |
Single Pass |
| GPS LOCATION |
None |
100m Accuracy |
COVERAGE:
- Global Coverage = a 406 MHz signal will be received from anywhere on Earth!
- Local Coverage (the satellite must view the beacon and a ground station simultaneously)
SIGNAL TYPE:
- Digital Signal
- Unique Identification Code (UIC)
- Linked to information about the vessel / aircraft and its owner
- Eliminates Non-Beacon false alarms
- Allows false alarms to be resolved with a phone call
- Analog Signal
- Anonymous
- Over 50% of false alerts from non-beacon sources
- False alarms must be tracked to source
ALERT TIME:
- Instantaneous = Geostationary satellites will receive a signal as soon as the beacon is activated.
- 2 Hours = A polar orbiting satellite must be overhead, may take up to two hours!
DOPPLER LOCATION:
- An accurate location can be determined using one satellite pass 95% of the time.
- At least two satellite passes are required to determine a location.
GPS LOCATION:
- Some 406 MHz beacons can transmit GPS positions with an accuracy of 100 meters. Geostationary satellites provide instantaneous locating!
- 121.5 MHz = No such capability due to analog signal
The bottom line is this. With a 406 beacon your distress signal will be received from anywhere on the planet, located accurately and quickly, and rescue forces will know who and what to look for. All these advantages add up to less time between beacon activation and rescue. Any rescuer knows that the sooner they get to you, the better your chances are.
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