AP losing NAV source

[jdpainter]

I'm using a Garmin 496 to drive my Dynon AP.  Occasionally I will see an error saying something like "NAV source lost".  

Is this normal behavior?  I'm told by one of the beta testers that this is because the 496 is prone to dropping packets.  

 

[dynonsupport]

We've heard of this happening on the occasional X96. It hasn't really been an issue since before the AP, it would be barely noticeable as the signal blips occasionally. How often does this happen?

 

[jdpainter]

This happens very consistently, probably every 5-10 minutes or so. When it happens I can immediately re-enable NAV mode.

 

[dynonsupport]

How do you have your serial output set up on your Garmin (NMEA settings, baud rate, etc)?

 

[timfwalsh01]

What are the correct settings for the Garmin 496?

Is the Garmin "setup menu" the correct place to change them? Thanks Tim

 

[dynonsupport]

You want NMEA out and then go into the advanced menu and choose "normal" not "fast." The 496 user guide tells you how to do all of this if you aren't familiar.

We have a table of GPS settings on our wiki page:

http://wiki.dynonavionics.com/GPS_Serial_Compatibility_and_Configuration_Settings

 

[timfwalsh01]

I found the secret screen!! In the Garmin 496 Owners Manual, page 124, It explains the procedures for the Advanced NMEA Output Setup.

Thanks, will head to the airport and see f I can get the HS34 to recognize two separate GPS units!!

Thanks Tim

 

[timfwalsh01]

OK,

I am having problems with output from the Garmin 496 being displayed on the HSI.

I have configured the 496 with the above instructions.  (I have EFIS-D10A, EMS-D10, HS34, AP74),

My HSI settings:
 
HS34 Serial Setup
    Serial One (This is my GNS-430)  Works no problem!!
     Input:         Aviation
     Output:       None
     Bud Rate:   9600

   Serial Two (Garmin 496)
    Input:          NMEA
    Output:        None
    Baud Rate:  9600

Assuming the wiring is correct (I have Approach Stack System), and the settings are as stated.  

What am I missing?  Tim

 

[dynonsupport]

Tim,
When you switch to the 496 on your HSI page (probably GPS2) using the NAV SRC button on the HS34, what does the screen show?

 

[timfwalsh01]

Your are correct, it is GPS2, and something like "searching for a signal."  

Which implies the settings are not correct - I think :-(

Tim

 

[dynonsupport]

Do you get the same message with the 496 powered off as you do with it powered on?

There aren't many settings to set. If you have these set right, then wiring is the next thing to check.

If you can, grab an ohmmeter and make sure the serial output pin on the 496 plug makes it to the serial 2 input pin on the HS34.

 

[timfwalsh01]

I have not tried powering the unit off - will do.

I will test wiring harness (maybe I just did not insert the connectros all the way - I can hope(.

Will let you know - thanks for the quick responses. Tim

 

[timfwalsh01]

OK,

I still cannot get my HSI to connect to my Garmin 496 (Serial Input 2)

I have confirmed that my Garmin 496 is in fact putting out a signal to Pin #2 on the Male DB-25 for the HS34.

To review, here are my current menu settings:

My HSI settings:

HS34 Serial Setup
   Serial One (This is my GNS-430)  Works no problem!!
    Input:         Aviation
    Output:       None
    Bud Rate:   9600

  Serial Two (Garmin 496)
   Input:          NMEA
   Output:        None
   Baud Rate:  9600

Garmin 496 Settings:
Product ( Setup > Interface > NMEA In and NMEA Out
             Baud 4800 (only option)

"Advanced NMEA Output Setup"
Output Rate > Normal

Lat/Lon Minute Precision        Waypoint IDs
"XX.XXXX (4 digits)"               "Numbers"

GPS Status (GSA, GSV)         Garmin Proprietary
"On"                                      "Off"

Waypoint/Route (WPL, RTE)
"Off"
Output Rate > Normal

Any thoughts?  Is there a certain Garmin software version I should be using?  Your assistance is greatly appreciated!!

I had six more hours on the autopilot/altitude hold.  The autopilot held rock steady, the altitude hold was not as rock steady on this flight.  I will go into more detail later.

Tim

 

[Brantel]

Unless the HS34 and the 496 are at the same baud rate, they will never talk to each other....

You state that the HS34 is at 9600 and the 496 is at 4800, either change the HS34 to 4800 or change the 496 to 9600.

One way to get the 496 to change to 9600 is to select either "TIS in/NMEA & VHF out" or "Aviation in/NMEA & VHF out"

 

[dynonsupport]

As Brian says, they need to be at the same data rate, and most customers run Aviation in/NMEA/VHF out, which gets you 9600 baud. If you don't do this, please adjust your HS34 settings to be 4800 baud.

 

[timfwalsh01]

I must confess I was using the settings outlined in the Wiki. I will switch to the above. Thanks Tim

 

[timfwalsh01]

I a happy to report that I finally have the Garmin 496 working along with my Garmin 430.

I changed the Garmin 496 settings to:  "TIS in/NMEA & VHF out", and the baud rate for both is 9600.

After reading the Wiki, I was under the impression ONLY those settings would work and focused a great deal of attention to the physical, and wiring installation.

I was thrilled to see the HSI come to life!!  I can now bring the 496 home, plug in a flight route, and fly it using the Dynon autopilot!!

Thanks for all your help  Tim  

 

[rvmills]

I just experienced the "NAV Source Lost" problem several times on a 2 hour X-C yesterday (D-100 and D-10A, Garmin 396). Happened perhaps 5-6 times in 2 hours. The AP went to TRK each time. Seems like a momentary loss...so fast in fact that by the time the error message was up I could just hit the NAV button, and the AP went right back to NAV (like Jaime described). On the Garmin I have Aviation In/NMEA & VHF out, with Advanced NMEA set to Normal. Dynon is set to NMEA/9600 Baud, or Auto/9600 (will check when I fly home tomorrow, and also make sure the D100 master and the D10A have the same settings).

Any thoughts on why this might be happening...seems very random, not at turn points, or any specific places, just occasional blips.

Thanks!!

Bob

 

[N707RW]

Hi Bob

I am one of the beta testers and I also have a GPS396, nearly the same setup you have. I get those nav src lost messages all the time as well.

What is happening here is the GPS gets backed up a little and outputs what is called "stale data". Then it catches up with itself and that happens pretty quickly. And that's why you can just reach up there and hit nav again and it seems to work just fine.

This is a known issue and I know the folks at Dynon are working the issue. The software has a time limit and recognizes that the data hasn't changed in that time, so it outputs the nav src lost message. It's possible that they might be able to vary the time limit or work some other magic, but for now the issue is just one of those annoying things that just happen. It is not a fault of the Dynon stuff, it is because the GPS just gets backed up a little.

There can be other causes for the message, such as losing total GPS lock (in which case you can't just re engage nav). But in your case, the stale data is what's going on here.

Hope this helps,

Rich Wilson

 

[rvmills]

Rich,

Thanks very much for the reply! I flew back today and tried Auto/Auto and NMEA/9600, and there was no change (same occasional and random event, maybe 4 times in 2.6 hrs)...kinda figured it must be in the signal. Good to know more, and thanks for the info!!

Like you said, not really a bother, just one of those little nags that it'd be nice to eliminate...and I'd classify it as pretty low pri.

It'll be interesting to see how the fix gets done, as you wouldn't want to impact safety by accepting data that is really old and stale. Not that critical in the enroute phase, but much more so in the terminal phase. Of course this is a VFR GPS, so we're not shooting approaches, where Required Nav Performance gets pretty important!

Hey, thanks again for passing the info and your experience along!!

Cheers,
Bob