GPS I/O Frequently Asked Questions

• How do I download position data from my GPS to my Beacon?

• How long does it take to down load position coordinates from my external GPS to my Beacon?

• How does the GPS data get from my GPS to the Beacon?

• Can I download information once my Beacon is turned on and activated?

• Does my Beacon need any special set up to accept GPS data from an external GPS?

• Does my GPS unit have to be set up in a special way to transmit position coordinates via the NMEA 0183 Interface?

• What is the maximum length my GPS cable can be?

• What happens if I plug the GPS into the Beacon first and press the GPS I or I/O button without waiting for the GPS to acquire satellites?

• What happens if I have downloaded GPS into my Beacon and the Onboard GPS engine acquires new GPS data (P/N 2798.4 only)?

• How long does the Beacon hold data in memory?

• How much power is needed to run the IR LED on the GPS cable?

Question: How do I download position data from my GPS to my Beacon?

Answer: You must have a NMEA 0183 version 1.5 or higher output ready GPS unit and a GPS Interface cable. The NMEA 0183 optical Interface connector supplied with your TerraFix must be connected to the GPS interface cable using a universal serial adapter. Turn on your GPS unit and allow it to acquire the necessary satellites. Make sure the output is set to NMEA 0183 with the GPGGA sentence configured if necessary. Connect the NMEA 0183 interface cable to the GPS unit and the TerraFix. The TerraFix will initiate a data preload when the GPS I or GPS I/O button is pressed for more than ½ second and less than 5 seconds.

Question: How long does it take to down load position coordinates from my external GPS to my Beacon?

Answer: Upon connection with a properly operating and fully acquired GPS unit, the ACR Beacon usually take less than four minutes to synchronize and download coordinates. Subsequent position updates will take from a few seconds to no more than 20 seconds to complete.

Question: How does the GPS data get from my GPS to the Beacon?

Answer:  The GPS unit transmits data as electrical energy through the GPS Interface cable to the ACR optical interfacing connector. The ACR optical interfacing connector has an infrared LED and sensor located in it. The electrical energy supplied by the GPS unit is converted to infrared light in the ACR optical interfacing plug. Data from the GPS unit is transmitted via infrared light to the Beacon through the translucent Beacon top cap or lens when the ACR optical Interface plug is properly engaged. The Beacon has an infrared detector that decodes the light pulses. ACR uses an optical Interface design to eliminate the potential for leaks and corrosion common to mechanically interfacing devices. An external LED flashes to confirm that GPS data is being sent from the handheld GPS.

Question: Can I download information once my Beacon is turned on and activated?

Answer:  No. You must download your GPS coordinates into the TerraFix™ prior to activating your Beacon. Once activated your Beacon will transmit your LAT/LON coordinates to the GEOSAR satellites. If no GPS data has been downloaded into the Beacon it will rely on the LEOSAR satellites to obtain the Beacon’s position using Doppler shift. If your Beacon contains an onboard GPS (P/N 2798.4) the GPS engine will be turned on upon activation and will search to acquire your LAT/LON.

Question: Does my Beacon need any special set up to accept GPS data from an external GPS?

Answer:  No. If it is hooked to a valid data source, that has been properly set up to deliver NMEA format with the GPGGA sentence, it will automatically attempt to download the data once the GPS I or GPS I/O button has been depressed and will form an emergency message that includes the position data when the preload function is initiated.

Question: Does my GPS unit have to be set up in a special way to transmit position coordinates via the NMEA 0183 Interface?

Answer:  For the GPS to transmit data, go to GPS setup and make sure the NMEA 0183 output is turned on and the GGA NMEA sentence is selected or turned on. Consult your GPS user’s manual for information on configuring the NMEA output.

Question: What is the maximum length my GPS cable can be?

Answer:  ACR Electronics recommends a maximum length of 400 feet using 24 AWG wire. Contact your GPS owner’s manual for more detailed information.

Question:  What happens if I plug the GPS into the Beacon first and press the GPS I or I/O button without waiting for the GPS to acquire satellites?

Answer:  The Beacon will function normally in the off position, but will not store GPS coordinates. As soon as the GPS has acquired satellites the data will be transferred to the Beacon. If the Beacon is activated no GPS data will be accepted and your Beacon will rely on the LEOSAR satellites to obtain its position by using Doppler shift.

Question:  What happens if I have downloaded GPS into my Beacon and the Onboard GPS engine acquires new GPS data (P/N 2798.4 only)?

Answer:  If external and internal GPS are present, the internal GPS data will have priority at activation. If the internal GPS has not been able to acquire your LAT/LON coordinates prior to your first burst, the downloaded GPS coordinates will accompany the UIN to the satellites. Once good navigational coordinates are obtained by the onboard GPS, these coordinates will be updated into the distress message and the downloaded coordinates will be eliminated.

Question:  How long does the Beacon hold data in memory?

Answer:  4 hours. If new GPS data has not been downloaded, the TerraFix will return to default mode and utilize the LEOSAR satellites to obtain the position using Doppler shift.

Question: How much power is needed to run the IR LED on the GPS cable?

Answer:  The minimum power needed is 3.3VDC and 2mA