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  #1  
Old 04-22-2011, 07:58 AM
rswalden's Avatar
rswalden rswalden is offline
 
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Default Configuring GPS Input to the new ACK 406 Mhz ELT

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,
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KFFC "Falcon RV Squadron" Peachtree City, GA
Full Throttle Airshows
RV-7A Tip-Up, IO-390, 1000+ Hours
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Last edited by rswalden : 07-08-2012 at 03:09 PM. Reason: Technical change...
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  #2  
Old 04-22-2011, 02:32 PM
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JordanGrant JordanGrant is offline
 
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Default thanks!

Thanks, Bob! I'll be installing one of those when I get back home from deployment - so I'm saving this post for sure.
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  #3  
Old 05-02-2011, 02:50 PM
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Noah Noah is offline
 
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Default

Great thread, thanks so much for posting this info. This is one of those little "undocumented features" that can really have you pulling your hair out and wasting hours and hours trying to figure out.

I am driving an AFS4500, Trutrak ADI, an Ack E04 ELT, and a Microtracker RTG with a Garmin GPS18X-5Hz. I wonder if changing to 2 digit precision on the $GPGGA data will hose me on any of the other devices. Anybody got any clue on that?

If it does, ugggh, I will need to install a 3rd GPS.

Thanks.
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All men dream, but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find that it was vanity: but the dreamers of the day are dangerous men, for they may act their dream with open eyes, to make it possible. -T.E. Lawrence
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  #4  
Old 05-02-2011, 05:25 PM
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AltonD AltonD is offline
 
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Quote:
Originally Posted by rswalden View Post
. . .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. . . .,
What does the SL30 do with the GPS data?
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  #5  
Old 05-02-2011, 08:17 PM
jwyatt jwyatt is offline
 
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Default

Quote:
Originally Posted by Noah View Post
I am driving an AFS4500, Trutrak ADI, an Ack E04 ELT, and a Microtracker RTG with a Garmin GPS18X-5Hz. I wonder if changing to 2 digit precision on the $GPGGA data will hose me on any of the other devices. Anybody got any clue on that?
I'm driving the same list of devices with the GPS-18x-5Hz, too (minus the ADI), and read this thread with interest, since I have the ACK ELT on order.

According to this lat/long distance calculator (assuming I used it correctly), 2-digit precision is about 60 feet in my area, and 4-digit precision is ~0.6 feet.

I also don't see any way in the config utility to configure the 18x to limit the data to 2-digits. According to the spec sheet, the 5Hz model sends 5-digit data by default, whether or not the fix is actually accurate to that level is another question.

It seems a shame to "dumb down" the GPS data to my primary navigation system to satisfy the ELT, even if that precision is probably not needed. So it seems the options would be:
- Install another GPS that will do 2-digit data to drive only the ELT. Run more power and data wires.
- Leave off the GPS from the ELT (and hope someone sees the crash on APRS).
- Install a different ELT that will handle the 9600 baud data stream. Much more $ for a GPS-capable model.

Pity that the ACK install manual didn't contain more specifics on the accepted data format.
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  #6  
Old 05-02-2011, 08:47 PM
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Quote:
Originally Posted by jwyatt View Post
According to this lat/long distance calculator (assuming I used it correctly), 2-digit precision is about 60 feet in my area, and 4-digit precision is ~0.6 feet.
Sounds right, since one minute of latitude is 1 nmi or 6076 ft, so .01 minutes would be ~60 ft.

AFS said this was definitely a bad idea to remove this much precision from the lat/lon data, and that their synthetic vision would be jumpy/erratic via an AFS forum post today. So I called ACK this evening and talked to Mike, who I think is the principal guy there. He insisted that they could handle 4 or 5 digit data, and that the assertion in this thread is a mistake (I forwarded this link to him, and invited him to come on here to personally correct it). He said that COSPAS only uses 2 digits of precision, and that they (Ack) truncate any data beyond 2 digits before transmitting it to COSPAS/SARSAT. No need to have the GPS truncate the data since the ELT does it.

In order to validate this, I made up their led test light and connected it up (my panel is all taken apart for painting & lettering so this was a bit of a pain) and I got the led lighting every second indicating that the ELT is receiving good GPS data (my GPS-18X 5Hz is not transmitting at 5Hz since the ADI can't handle that).

Unfortunately, I ran out of time tonight before hooking up a terminal emulator to get a look at the data coming from the GPS, but according to the Garmin GPS-18X manual the default is 5 digits after the decimal precision (p.17). I agree, I don't even see a way to decrease the precision of the data being output in the $GPGGA sentence.
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All men dream, but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find that it was vanity: but the dreamers of the day are dangerous men, for they may act their dream with open eyes, to make it possible. -T.E. Lawrence
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  #7  
Old 05-02-2011, 08:55 PM
jwyatt jwyatt is offline
 
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Quote:
Originally Posted by Noah View Post
I called ACK this evening and talked to Mike, who I think is the principal guy there. He insisted that they could handle 4 or 5 digit data ...
I made up their led test light and connected it up and I got the led lighting every second indicating that the ELT is receiving good GPS data.
Noah, thanks for your investigation efforts! I just saw the AFS thread as well, and was going to talk to ACK tomorrow. Looks like time to just keep on keepin' on.
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  #8  
Old 05-03-2011, 01:28 PM
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rswalden rswalden is offline
 
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Quote:
Originally Posted by AltonD View Post
What does the SL30 do with the GPS data?
Alton,
The Garmin 496 (and others) will send navaid ID and nearby airport frequency information to the SL-30 standby window along your programmed route of flight. This makes it a snap to contact tower, ground, clearance delivery, etc.... without having to look up the info. Great feature.
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Full Throttle Airshows
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  #9  
Old 05-03-2011, 02:09 PM
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uk_figs uk_figs is offline
 
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Default 496 to SL30

Not to hijack the thread but I have this hooked up but does not seem to work (496 RS232 to SL30 Pin 4). Do you have to have a route loaded versus a simple GOTO direct? maybe I am missing some setup setting.
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  #10  
Old 05-06-2011, 03:50 PM
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Just to follow up, I did hook up a PC to my GPS via hyperterminal, and confirmed that I was sending ddmm.mmmmm lat/lon data in the $GPGGA message, and the ELT seemed to like that data by blinking the test LED once per second. Not sure why I got a different result than Waldo.
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All men dream, but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find that it was vanity: but the dreamers of the day are dangerous men, for they may act their dream with open eyes, to make it possible. -T.E. Lawrence
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