What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

GTN650 suddenly can't hold it's position

S

Sig600

Well Known Member
Anyone seen this before?

My GTN650 has started just randomly losing satellites, and dropping position. Usually pulling the breaker and cycling the power will get it back. Yesterday it took several minutes to acquire. The satellite status page will just be grey bars going up and down, every now and then one will turn green then go away. Then, like it's had some stroke of brilliance they'll all light up and turn blue and I'm off. Then sometime later my Skyview will announce GPS1 FAIL and we're at it again.

At first I thought there may be interference but the antenna is located right next to the skyview antenna and the dynon holds 9 satellites while the Garmin is struggling.

This is a new development in the last few flights. Pretty sad if this $10K piece of gear is failing at 100 hours.

Thoughts?

ckl4w.jpg
 
Last edited:
Sounds like yet another possible GA35 antenna failure. Do you have a friend nearby who would be kind enough to swap GPS antennas with you for a flight?
 
krw5927 said:
Sounds like yet another possible GA35 antenna failure. Do you have a friend nearby who would be kind enough to swap GPS antennas with you for a flight?
Click to expand...

I concur........

I went through very similar issues this past fall. The first couple times, power cycling would work in the air, then it wouldn't.

Unfortunately, I purchased mine too early and by the time I made my first flight, it was out of warranty.

1. Check for shorts in the antenna cable, wiggle the cable to attempt to find that rogue shield wire causing issues
2. Ensure that the connectors are properly terminated
3. Swap out the GPS antenna

I had a GA-35 that went bad. There is a rumor going around that a batch of them failed due to over torqueing the mounting bolts, causing cracks in the shell, then water getting into the antenna. I know that wasn't accurate in my case. I measured the torque and my RV hadn't been rained on.

I bought a new GA-35, swapped it out, and everything is just fine now. I had made the decision to eat any restocking fees if the problem persisted after the antenna swap.

I personally believe that Garmin had a bad batch of antennas a couple years ago. Because the warranty tends to expire on experimental builders before the first flight, they are now reaping the benefits by not having to replace these units under warranty. This is just another reason to purchase your expensive avionics at the last minute to maximize your warranty coverage.
 
I have found both the G3X team guys and the usual Garmin dealers will go way out of their way to help you correct issues like this and will bend the rules when justified to get you fixed up.
 
Walt said:
I have found both the G3X team guys and the usual Garmin dealers will go way out of their way to help you correct issues like this and will bend the rules when justified to get you fixed up.
Click to expand...

I don't think that's universal with Garmin, but I do agree about the dealer participation. My dealer did go to bat for me and worked very closely with me in troubleshooting. They basically hit a stone wall Garmin due to the warranty period. It certainly had changed my perception (negatively) of Garmin support.

I don't think the G3X team was involved. I don't have a G3X, just a GTN650.

bob
 
Just curious if this happened with a 2020 ADS-B compliant system in controlled airspace and the failing antenna took out your second certified GPS system , would this cause a lost position for ATC, if and when they do away with SSR?
 
I think it is important and in our best interest for us experimental guys to always work with/through TeamX.

While the GNS/GTN may not be in their department, they eat lunch with people that are responsible for those products.

It is important to realize that TeamX and the certified sections of Garmin are very different in nature but TeamX has proven that they will try their best to bridge the gap!
 
Last edited:
rleffler said:
I concur........

I went through very similar issues this past fall. The first couple times, power cycling would work in the air, then it wouldn't.

Unfortunately, I purchased mine too early and by the time I made my first flight, it was out of warranty.

1. Check for shorts in the antenna cable, wiggle the cable to attempt to find that rogue shield wire causing issues
2. Ensure that the connectors are properly terminated
3. Swap out the GPS antenna

I had a GA-35 that went bad. There is a rumor going around that a batch of them failed due to over torqueing the mounting bolts, causing cracks in the shell, then water getting into the antenna. I know that wasn't accurate in my case. I measured the torque and my RV hadn't been rained on.

I bought a new GA-35, swapped it out, and everything is just fine now. I had made the decision to eat any restocking fees if the problem persisted after the antenna swap.

I personally believe that Garmin had a bad batch of antennas a couple years ago. Because the warranty tends to expire on experimental builders before the first flight, they are now reaping the benefits by not having to replace these units under warranty. This is just another reason to purchase your expensive avionics at the last minute to maximize your warranty coverage.
Click to expand...

My antennas are under the cowl, never been washed let alone rained on. Swapping the antenna sounds like the next logical step. I have an email out to Garmin, I'll post what I hear back.
 
Just to be sure, next time turn off the Dynon gps. It is possible for one antenna to interfere with another if it's the Dynon's electronics which have an issue. Not likely, but easy to check.
 
Any idea of production date-S/N range of failed units?

If there is a bad batch, Garmin does not make these, right? Isn't it Aeroantenna?

What are the serial numbers of the failed units. Mine might have been made at the same time. I would like to know.
 
krw5927 said:
Sounds like yet another possible GA35 antenna failure. Do you have a friend nearby who would be kind enough to swap GPS antennas with you for a flight?
Click to expand...

If you are in Reno--------hop over the hill to O61-----I have a NIB antenna you can put in for a test run.
 
Sig600 said:
Anyone seen this before?

My GTN650 has started just randomly losing satellites, and dropping position. Usually pulling the breaker and cycling the power will get it back. Yesterday it took several minutes to acquire. The satellite status page will just be grey bars going up and down, every now and then one will turn green then go away. Then, like it's had some stroke of brilliance they'll all light up and turn blue and I'm off. Then sometime later my Skyview will announce GPS1 FAIL and we're at it again.

At first I thought there may be interference but the antenna is located right next to the skyview antenna and the dynon holds 9 satellites while the Garmin is struggling.

This is a new development in the last few flights. Pretty sad if this $10K piece of gear is failing at 100 hours.



Thoughts?

ckl4w.jpg
Click to expand...


The latest revision in the GTN650 install manual (rev. L)
page 3-8
states: 12 inches between antennas is preferable and less than 9 inches WILL result in antenna degradation!

How about moving the beloved Skyview antenna and see how it all works?;)
 
jthocker said:
The latest revision in the GTN650 install manual (rev. L)
page 3-8
states: 12 inches between antennas is preferable and less than 9 inches WILL result in antenna degradation!

How about moving the beloved Skyview antenna and see how it all works?;)
Click to expand...

Thanks John, I'll be installing mine (G3X, GDL39R, and GTN 650) soon. I had planned under cowl, but now the geometry for that has changed. Most of us don't have an install manual. Is it available now?
 
jthocker said:
The latest revision in the GTN650 install manual (rev. L)
page 3-8
states: 12 inches between antennas is preferable and less than 9 inches WILL result in antenna degradation!

How about moving the beloved Skyview antenna and see how it all works?;)
Click to expand...

That's what stein says... Still confused me that it would be just fine for 100 hours and the poof.
 
Sig600 said:
My antennas are under the cowl, never been washed let alone rained on. Swapping the antenna sounds like the next logical step. I have an email out to Garmin, I'll post what I hear back.
Click to expand...

We've found that under the cowling is not the greatest location for GPS antennas. The heat tends to get to them and damage them fairly quickly. They were never designed to operate in that kind of thermal environment. Most of the heating takes place after shutdown. Let alone the issues of shading everything aft of the antenna close to the horizon. I would recommend mounting your replacement antena somewhere else.
 
avionicsr said:
We've found that under the cowling is not the greatest location for GPS antennas. The heat tends to get to them and damage them fairly quickly. They were never designed to operate in that kind of thermal environment. Most of the heating takes place after shutdown. Let alone the issues of shading everything aft of the antenna close to the horizon. I would recommend mounting your replacement antena somewhere else.
Click to expand...

So -what is the max allowed temp. Even the top of a fuse is pretty hot in Tuscon in the summer.

Here is a funny link - http://sarasotaavionics.com/avionics/at2300-326
It says the temp range is -500C to +700C. Wow, below absolute zero and hotter than the exhaust!
 
SAME PROBLEM, GETTING A WARRANTY REPLACEMENT

I had this problem ever since I installed the GTN650 about two years ago. I am not using it for IFR yet, and I have a Dynon Skyview working perfectly, so I had let it go until now. I was basically just out of warranty. I emailed support at Garmin, and they authorized a replacement to be sent out by my original vendor, Sarasota Avionics. Today I filled out a Sarasota Avionics RMA online request, and had an immediate RMA. I had good email support from both Garmin and Sarasota about my request for a replacement antenna. This makes me wonder if both know of problems with this antenna. My installation is under the cowling on a RV-9A. It would happen intermittently, sometimes only once per flight. At first I thought it was from the aircraft attitude, and the antenna shadowed by the firewall somewhat. But, it would also happen in level flight. The obvious issue was that one second I would have 10 or more satellites, and then the next second they would all be gone, and it would be slowly establishing contact with them again. This could also be due to a cable issue, with the power supply for the antenna going away. I checked my cables and as far as I could tell, they were good. I appreciate the support I received from Garmin and Sarasota Avionics on this one.
 
Update: Replacement Antenna solves the problem

The problem I was having with losing satellites has been resolved by replacing the GPS antenna. I have been on several flights since changing the antenna and I have had no further issues.
 
ILevil device will cause this problem too

I bought one of those iLevil ADSB receivers and put it up on the glare shield near my Garmin puck. My 400W started losing satellites until I moved the iLevil.
 
Competing GPS Antennae

I was working in my cockpit the other day and decided to test the problem of signal loss when other GPS antennae are placed near the antenna for my 400W. I turned my 400W and my iLevil ADSB/GPS receivers on with the 400W on the satellite status page. When the iLevil was over 12" away all my satellite bars were full or nearly so. As I moved the iLevil slowly closer to the Garmin antenna the bars immediately began to go down. When the antennae were about 6" apart the bars indicated about half strength. When the antennae were right next to each other the 400W's status bars were barely showing. When I turned the iLevil off, the status bars immediately began to move back to full strength.

I didn't realize that GPS antennae compete for GPS signal or interfere with each other. I probably would have mounted my Garmin antenna on the fuselage behind the canopy if I had it to do over. John
 
jpowell13 said:
I was working in my cockpit the other day and decided to test the problem of signal loss when other GPS antennae are placed near the antenna for my 400W. I turned my 400W and my iLevil ADSB/GPS receivers on with the 400W on the satellite status page. When the iLevil was over 12" away all my satellite bars were full or nearly so. As I moved the iLevil slowly closer to the Garmin antenna the bars immediately began to go down. When the antennae were about 6" apart the bars indicated about half strength. When the antennae were right next to each other the 400W's status bars were barely showing. When I turned the iLevil off, the status bars immediately began to move back to full strength.

I didn't realize that GPS antennae compete for GPS signal or interfere with each other. I probably would have mounted my Garmin antenna on the fuselage behind the canopy if I had it to do over. John
Click to expand...

Hello John,

Remember that any radio receiver also contains a tiny transmitter, which puts out some radio-frequency noise of its own. Depending on how well-designed a receiver is, it may emit enough noise to cause interference with neighboring receivers.*

Meanwhile, the GPS satellites overhead are about halfway to geostationary orbit, and they transmit with the approximate power of a fifty-watt light bulb. Imagine standing in a field on a dark night trying to spot a porch light twelve thousand miles away, while your neighbor is simultaneously shining his pocket flashlight in your eye from a distance of twelve inches, and you begin to get an idea of some of the challenges faced by a GPS receiver.

Frankly, when you stop to think about it, it's sort of amazing this whole setup works well enough for us to fly instrument approaches with! No doubt about it, these systems were designed by some smart folks... but you have to do your part by giving the equipment a quiet environment to operate in. That's why the GNS 4xxW installation manual says, in part:

The GPS antenna should be mounted no closer than two feet from any [...] antenna which may emit harmonic interference at the GPS L1 frequency of 1575.42 MHz
Click to expand...

- Matt

* This is a greatly simplified explanation. For a more in-depth treatment, fix yourself a cup of coffee and google "superheterodyne receiver local oscillator radiation".
 
Last edited:
I am kinda late to the conversation but while we are on the subject. I have my G3X gps puck about 6" from my GTN650 antenna and have never lost link on either.
Is this setup a problem Matt?
I have no idea if either has a gps L1 frequency of 1575.42 MHz
 
MarkW said:
I have no idea if either has a gps L1 frequency of 1575.42 MHz
Click to expand...

I think all gps boxes receive this frequency.
I'd repeat the above experiment. Turn one gps off, look at the signal strength bars on the other, then turn the first one back on, see if they go down.
 
Just wanted to update this thread.

I experienced exactly these symptoms on my GTN650 too.
Mostly on ground, just around the time I was done with the run-up, or shortly after take-off. GPS would come back online after about 2 minutes, and stay on for the remainder of the flight.

First exchanged the GPS antenna, as over-torquing the mounting screws will cause these kind of problems. No joy.
Then we had another GPS cable made, with an souther braid to reduce any interference. Same again. No joy.

Tried the GTN in a SR22 which had no reported problems. Boom. Same symptoms there.
So it was something wrong with the GTN from the factory.
Unit repaired, and all symptoms gone.


It can be the unit itself too.


Espen
 
mine does this, to further complicate my situation- the GA35's were the original ones from my 430/530 install that this 750/650 replaced

I've never had issue with the 430/530, the 650/750 will drop occasionally, sometimes a reset fixes it, sometimes not
 
You must log in or register to reply here.
Back
Top