This describes the GPS interface requirements for installing your new ACK 406 Mhz ELT.
I UPDATED THIS WITH TECHNICAL CHANGES on 08 July 2012:
The ACK E-04 406 MHZ ELT kit is a great value, considering it costs $1000 less than the nearest rival GPS-capable ELT. I received mine through Aircraft Spruce after waiting more than a year for its certification and delivery. Although setting up the unit to receive GPS position is NOT REQUIRED, it only makes sense to use this feature if you’re serious about getting rescued. Installation was straightforward except for one roadblock I encountered in trying to get my Garmin 496 GPS to communicate with the ELT.
To use the GPS feature, you need to run a shielded 3-conductor wire to the unit that provides DC power (protected by 1 amp fuse or circuit breaker), a ground, and the serial output from your GPS. The instruction manual describes how to connect these to the 4-pin mini-din female connector that is provided. Unless you are a neurosurgeon, soldering these small wires to the back of the plug is challenging. I simply crimped the wires to gold-plated female DB connector pins (the smaller high-density type used for radios) and slid them snuggly over the solder pins on the back of the ELT mini-din plug & used heat shrink to secure them. Double check to make sure the power, ground, and GPS signal lines are on the correct pins!
Here’s how I configured my Garmin 496 (yours will be similar)
1. Select MENU, then SETUP, then INTERFACE
2. Select Serial Data Format = “TIS In/NMEA & VHF Out”
3. Select Baud = 9600
4. While in this screen, select MENU again and select “Advanced NMEA Setup”
5. Select Output Rate = Normal/Fast
6. Select Lat/Lon Precision = 2, 3, or 4-digit precision (any will work)
The ACK ELT provides a STATUS line that indicates whether a valid GPS signal is being received by the ELT. The instruction manual has you make a little tester unit consisting of an LED, resistor, and alligator wire clips… but a small voltmeter is very useful to ensure your power leads are correct. With power provided to the unit through the mini-din connector, the STATUS line from the ELT will read approximately –5.5 volts. If a valid position is being sent, the STATUS line will give a short burst to +5 volts that is too fast for your meter to detect. The LED tester will give a very short blink every second if the ELT is recognizing a valid GPS signal. You can also view the +5 volt spike on an oscilloscope if you have one.
If you fail to get a pulse on the STATUS line, be sure your Garmin GPS is outputting data at 9600 baud. The ELT default bit rate is internally set at 9600 baud. If your Garmin GPS output data rate is other than 9600, you’ll have to take the ELT apart and jumper it to the slower rate (yikes).
Still having trouble getting a valid STAUS signal? If you have access to a laptop with Windows XP, you can run its HyperTerminal program through a serial port or adaptor and take a look at the data stream your GPS is sending. When your GPS is locked on and receiving a VALID GPS LAT/LON, the following text string will appear in the data stream (along with a lot of other data)…
$GPGGA,161907,3321.67,N,08434.25,W,1,00,3.2,221.7,M,-30.7,M,,*78
The $GPGGA tells the ACK ELT that this is a VALID lat/lon. The next values are time, latitude, N/S, longitude, E/W… and the rest of the line is ignored. The $GPGGA code must be present or else the ACK ELT will refuse to accept the data from the GPS.
You should now be transmitting a valid data stream to the ELT, provided you have GPS reception.
Hopefully, this will make your GPS/installation a little easier. By the way, my Garmin 496 data line drives four devices without any problem: my Dynon D-180 EFIS, the Garmin SL-30 comm/nav, the TruTrak autopilot, and now my ACK ELT. The RS-232 voltage/signal output from the 496 is robust enough to drive several devices.
Happy Flying,
I UPDATED THIS WITH TECHNICAL CHANGES on 08 July 2012:
The ACK E-04 406 MHZ ELT kit is a great value, considering it costs $1000 less than the nearest rival GPS-capable ELT. I received mine through Aircraft Spruce after waiting more than a year for its certification and delivery. Although setting up the unit to receive GPS position is NOT REQUIRED, it only makes sense to use this feature if you’re serious about getting rescued. Installation was straightforward except for one roadblock I encountered in trying to get my Garmin 496 GPS to communicate with the ELT.
To use the GPS feature, you need to run a shielded 3-conductor wire to the unit that provides DC power (protected by 1 amp fuse or circuit breaker), a ground, and the serial output from your GPS. The instruction manual describes how to connect these to the 4-pin mini-din female connector that is provided. Unless you are a neurosurgeon, soldering these small wires to the back of the plug is challenging. I simply crimped the wires to gold-plated female DB connector pins (the smaller high-density type used for radios) and slid them snuggly over the solder pins on the back of the ELT mini-din plug & used heat shrink to secure them. Double check to make sure the power, ground, and GPS signal lines are on the correct pins!
Here’s how I configured my Garmin 496 (yours will be similar)
1. Select MENU, then SETUP, then INTERFACE
2. Select Serial Data Format = “TIS In/NMEA & VHF Out”
3. Select Baud = 9600
4. While in this screen, select MENU again and select “Advanced NMEA Setup”
5. Select Output Rate = Normal/Fast
6. Select Lat/Lon Precision = 2, 3, or 4-digit precision (any will work)
The ACK ELT provides a STATUS line that indicates whether a valid GPS signal is being received by the ELT. The instruction manual has you make a little tester unit consisting of an LED, resistor, and alligator wire clips… but a small voltmeter is very useful to ensure your power leads are correct. With power provided to the unit through the mini-din connector, the STATUS line from the ELT will read approximately –5.5 volts. If a valid position is being sent, the STATUS line will give a short burst to +5 volts that is too fast for your meter to detect. The LED tester will give a very short blink every second if the ELT is recognizing a valid GPS signal. You can also view the +5 volt spike on an oscilloscope if you have one.
If you fail to get a pulse on the STATUS line, be sure your Garmin GPS is outputting data at 9600 baud. The ELT default bit rate is internally set at 9600 baud. If your Garmin GPS output data rate is other than 9600, you’ll have to take the ELT apart and jumper it to the slower rate (yikes).
Still having trouble getting a valid STAUS signal? If you have access to a laptop with Windows XP, you can run its HyperTerminal program through a serial port or adaptor and take a look at the data stream your GPS is sending. When your GPS is locked on and receiving a VALID GPS LAT/LON, the following text string will appear in the data stream (along with a lot of other data)…
$GPGGA,161907,3321.67,N,08434.25,W,1,00,3.2,221.7,M,-30.7,M,,*78
The $GPGGA tells the ACK ELT that this is a VALID lat/lon. The next values are time, latitude, N/S, longitude, E/W… and the rest of the line is ignored. The $GPGGA code must be present or else the ACK ELT will refuse to accept the data from the GPS.
You should now be transmitting a valid data stream to the ELT, provided you have GPS reception.
Hopefully, this will make your GPS/installation a little easier. By the way, my Garmin 496 data line drives four devices without any problem: my Dynon D-180 EFIS, the Garmin SL-30 comm/nav, the TruTrak autopilot, and now my ACK ELT. The RS-232 voltage/signal output from the 496 is robust enough to drive several devices.
Happy Flying,
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