ON Operation

To go from normal (ARM) to ON operation, the ELT needs a change of switch position from one of these sources:

· G-switch

· Control panel switch

· ELT front panel switch.

A G-switch jumper wire prevents the ELT from accidental operation while the unit is in transit to the airplane.

The jumper wire arms the G-switch only when the unit front connector is connected. When the switch is armed, the switch changes position when it senses a large change in velocity.

The control panel switch lets you manually start ELT transmission. When you put the control panel switch to ON, an EXT ON signal goes from the control panel to the ELT. This signal manually starts the transmitter from the control panel.

The ELT front panel switch also lets you manually start the transmitter. You do this when you put the front panel switch to ON.

The latching circuit holds the ELT on when it receives a change in switch position. This circuit sends a signal to the processor and the front panel ON indicator. When the ELT is on, the processor commands the two transmitters to send the emergency signals. The ON indicator flashes continuously.

A transmitter uses 121.5 MHz and 243.0 MHz carrier frequencies. This transmitter sends both frequencies at the

same time on the same transmission line. These frequencies are amplitude modulated with an audio frequency. This audio frequency sweeps continously from about 1600 Hz to 300 Hz.

This gives a homing signal for the search and rescue personnel.

Search and rescue satellites detect the 121.5 Mhz and 243.0 Mhz transmissions and send these signals back to ground stations. The ground stations receive and process the 121.5 MHz signal to find the location of the ELT. It gives a location accuracy of about 20 km.

The 121.5/243.0 MHz transmitter operates until the battery pack becomes unserviceable. The battery pack power lasts for at least 72 hours.

The other transmitter uses a 406.0 MHz carrier. This transmitter gives information to locate and identify the ELT.

The processor

The processor synchronizes the operation of both transmitters. Only one transmitter is on at a time. Every 50 seconds, the processor turns off the 121.5/243.0 transmission for a short time (440 msec) and commands the 406.0 MHz transmitter to send its signal.

Satellites detect the emergency signals from the 406.0 MHz transmitter and send this information to ground stations. The ground stations receive and process the emergency signals to find the location of the ELT. The 406.0 MHz transmitter gives a location accuracy of about 3 km.

The 406.0 MHz transmitter also give this information for the search and rescue personnel:

· Serial number of the ELT

· Country code

· ELT manufacturer.

The 406.0 MHz transmitter operates for 24 hours and then shuts down to conserve power.

Reset

The RESET 1 and RESET 2 inputs from the control panel let you turn off the transmitter when it comes on accidently. These inputs turn off the transmitter when you put the control panel switch from ARM to ON and immediately back to ARM.

You can also turn off the transmitter when you put the ELT front panel switch from OFF to ON and immediately back to OFF.