GTN650 excessive time to get initial 3D position

[pecanflyboy]

Originally Posted by Pdtofly

A few years ago, Gamin had a batch of bad GA-35 antennas. So it could be bad. Since you already swapped out the radio, I would swap the antenna out next.

Another thing to check, since it might be a temperature problem, check the antenna connectors on both ends. If the center pin was soldered, it could have a cold sold joint, and temperatures can effect that. Also check the cable.

Brian

I've not heard about the bad batch of GA-35's. Garmin is sending me a new antenna, so that is next. I'm not sure how that affects the issue. I still think it's the unit loosing its position and time and going into and "initial" acquisition mode. The GPS System screen shows no satellites until it finds the first one, and then it unzips them in 30 seconds and I have a position.

[John Tierney]

I see you are and RV-6, but you don't note which canopy. My RV-7 Slider frame causes errors with my GNS-480 antenna, mounted on the upper fuselage behind the baggage bulkhead. It finds satellites but gives me integrity errors on the ground with the sliding canopy open. The antenna doesn't like the canopy steel framework with my Kroger sunshade wires.

[Planecrazy232]

Originally Posted by pecanflyboy

That's a good observation. My initial thought was that a recent software upload may have been the culprit. Of course, troubleshooting that issue is difficult.

The manual states that the "initial" position acquisition can take as long as 20 minutes, but subsequent acquisition should be shorter. It's taken more the 30 minutes to get a position if the aircraft has been unpowered for more than 2 weeks.

In my view 5-30 minutes is excessive. It's not inertial nav. I should not have to wait at the end of the runway for my ADSB WAAS to find itself. Especially when the G3X does it in 30 seconds.

I just looked at my logs and I can absolutely say the delays started happening after installation of v6.7 software in the GTN.

[pecanflyboy]

Originally Posted by Planecrazy232

I just looked at my logs and I can absolutely say the delays started happening after installation of v6.7 software in the GTN.

That update came out in February, and my problems started last fall? I'll bring it up to Garmin. I remember when I first started troubleshooting that I had asked about the update. But, you know how that works. "Not in the software," and then everything starts working again with a new update.

[pecanflyboy]

Originally Posted by John Tierney

I see you are and RV-6, but you don't note which canopy. My RV-7 Slider frame causes errors with my GNS-480 antenna, mounted on the upper fuselage behind the baggage bulkhead. It finds satellites but gives me integrity errors on the ground with the sliding canopy open. The antenna doesn't like the canopy steel framework with my Kroger sunshade wires.

I love you guys. You make me think of everything. I do have a slider that covers the antenna when the canopy is aft. However, I still don't get antenna reception 20-30 minutes after the canopy is closed and flying. I see no satellites.

[BobTurner]

Try this: pull the aircraft to where it has a good view of the sky. Close the canopy, and only then power up the gps. Does it acquire a fix within a few minutes?

[pecanflyboy]

Garmin sent me a replacement GA-35 antenna. I cleaned the ground plane and connections. Checked for 4.7V at the antenna. Coax continuity was good. Moved aircraft away from the hangar and close the canopy. Turned off all other electronics.

INITIAL acquisition took over 10 minutes. I noticed that the GTN was looking for the same satellites as the G3X (which took less than 30 seconds to acquire 3D position). Another interesting observation was that I did not have the semi-transparent "ghost" bars above the GTN satellites. Once I did see the "ghost" bars I had 3D position within a minute.

SUBSEQUENT start ups consistently gave me a GTN 3D position within 90 seconds. I also had the "ghost" bars immediately.

The only thing left to replace is the RG-400 coax which will be a major ordeal. I can't see that it's the coax or the installation as I get consistent rapid acquisition after the initial.

Garmin tells me that I should have a 3D position within 2 minutes.

Has anyone else had this issue after the 6.7 update?

[lr172]

Originally Posted by pecanflyboy

Another interesting observation was that I did not have the semi-transparent "ghost" bars above the GTN satellites. Once I did see the "ghost" bars I had 3D position within a minute.

SUBSEQUENT start ups consistently gave me a GTN 3D position within 90 seconds. I also had the "ghost" bars immediately.

Still sounds like a position / date time issue. I believe the unit looks for one satellite first to positively identify it's location in the sky and get it's broadcast date/time. It then uses the internal table to map where all of the other satellites should be. That is when the ghost bars show up (unit now knows where they are and just need to confirm reception from those postions. Unit needs to fine tune each sat's location based upon signal strength. GPS antennae must be told where in the sky to look for each signal. They are not omni directional like VHF antennae.

That fact that a shut down and restart will give you a quick synch up points to the fact that the unit is not maintaining the aircraft's position or current time over the long haul (or is somehow lost or corrupted) and spends a lot of time searching. Having a good aircraft locatoin and time will allow the GPS to quickly find the first sat. If that doesn't work, it must spend a lot of time searching for it.

Larry

[BobTurner]

I just re-read your first post. This should be under warrantee. Contact the Garmin exp rep (here on VAF) and get him on-board.

[pecanflyboy]

Originally Posted by BobTurner

I just re-read your first post. This should be under warrantee. Contact the Garmin exp rep (here on VAF) and get him on-board.

It?s all been under warranty. Garmin has replaced the new unit with a refurbished unit. Garmin has replaced the antenna. Fortunately, I?ve been able to do all the labor. They?ve been very supportive and patient. However, the problem still exists. I suspect there are others that just tolerate it. My issue is that I?m based at a field very near a Mode C vail which requires ADSB. I have to wait for the GTN to find itself before I takeoff.