uk_figs

uk_figs

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Had an interesting situation with the GDL39 and XM weather and 796 today, flying in Oklahoma the 796 showed a solid GPS signal but the XM signal showed full green bars for a few seconds and then dropped to two red bars then the signal disappeared for a second. This cycle repeated for the entire first leg of the flight and I never received XM weather, tried cycling the power on the XM antenna and checked the music which played when the bars were green then stopped when the signal dropped. I assumed it was a XM problem.
The XM antenna is on the glareshield and was about 6 inches from the GDL39 unit which is also currently on the glareshield on the passenger side. On the flight back I had the same problem and wondered if there was interference from the GDL39 antenna so I switched the GDL39 off and lo and behold the XM signal showed full strength and the XM weather showed up a few minutes later. Any one else experienced this? I am planning to eventually remote the GDL39 but am wondering how far apart the two antennas should be to work in the meantime, looks like the maximum I can get on the glareshield is about 12 inches.
Not a big deal right now as we do not have coverage in OK until next year but would like to understand if this is interference as I have plans to move the 796 and GDL39 between two aircraft in the future.
Comments?
 
Never experienced this when I was using both. Had em right next to each other.

Now I have Discontinued XM so I can't try and repeat your issue.
 
Brantel
Thanks for the data point, I will check on my next flight to see if it is repeatable or just a coincidence with a broadcast/reception XM problem.
 
When I was using them together, I was on older firmware. There may be some issue with the new firmware that there was not with the older version...

Who knows. Sorry I can't try and repeat the issue now. It helps the vendors prioritize issues if they know it is more than an isolated incident.

The GDL-39 is a complex device so I guess it is possible that it could interfere with the reception on the XM antenna even though it is only a receiver. Modern electronics are full of oscillators, switching power supplies, DC to DC converters etc. that can cause interferance to outside devices that are nearby.

If it turns out to be a real issue, I am sure Garmin will work on it or recommend a minimum separation distance.
 
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XM Reception

Hello Dave,

While antenna shading can occur where antennas are mounted adjacent to other devices, we have flown one G3X aircraft for thousands of miles with a GA-26C GPS antenna, GA-26XM XM antenna, and an entire GDL-39 with antennas mounted together and almost touching without any signs of a problem.

The aircraft was flown for several hours yesterday (in the KC area North of you) with no XM or FIS-B reception problems noted.

We will test a GXM-40 XM receiver next to a GDL-39 and see if we can learn anything.

Thanks,
Steve
 
S/W up to date

Steve
When the XM signal locked in reception was solid. As far as I know all the software is up to date for 796, GDL39 and GXM 40, I will probably be flying to LOE next Saturday so will check if the same issue occurs. I have moved the GXM40 to the pilot side and the GDL antenna as far to the pax side on the glareshield as it can go. If the problem reoccurs and there are some specific tests you want me to try just let me know.
I do not have FIS-B uplink in my area only air-to-air (at least at 4500ft)
 
Dave,

I didn't fly, but I drove for about an hour today with a GDL39 and a GXM40 sitting on the dash touching each other and both connected to an Aera with cabling. I was using the latest software. Everything worked fine including XM weather and music.

Were you using a wired or a Bluetooth connection to the GDL39?

Thanks,
Steve
 
Wired connection

Steve
Have the GDL39 hard wired using the bare cable, same with the 796. Maybe I was having an XM problem and it was just a coincidence, I will check again this weekend.
I assume the antenna is passive so the fact that we have no FIS-B yet would not be a piece of the puzzle (i.e the unit searching for a non existent signal)
 
More Testing Results

Dave,

I recognize that you were not using Bluetooth, but I went ahead and did some additional testing this morning anyway.

In this test I had a GDL39 connected to an Aera 796 via Bluetooth and a GXM40 via cable. The weather source selection was setup for Auto (XM or FIS-B), and the GDL39 was in a location where it was not receiving FIS-B from a ground station.

Additionally, I placed the GDL39 immediately to the side and touching the GXM40.

I saw the bit error rate go up slightly for the XM weather feed, but the XM weather still worked great and the Aera properly used the XM weather source over the non-available FIS-B source.

If we think of anything else that might help explain what you have seen, we will let you know.

Thanks,
Steve
 
Flight testing results

I tested the system yesterday on the flight over to LOE and have a repeatable situation. Started out exhibiting the same behavior, turn on the GDL 39 and the 796 XM signal cycled between full signal and no signal, turned off the GDL 39 and the XM signal went to full strength. Seperated the XM antenna and the GDL 39 on each side of the glareshield and the XM signal stayed at full strength.
After moving the units around to various locations on the glareshield I figured out that it is NOT the GDL 39 antenna that is causing the problem it is the ferrite ring on the GDL 39 bare wire power cable that is the issue. In my installation as it was a retrofit the ferrite ring is on the glareshield as I could not fit it through the preexisting hole in the dash for on-glareshield wiring, each time I moved the XM antenna near the ferrite ring with the GDL 39 powered on the XM signal started to cycle, as I moved the antenna away the signal returned to full strength. As long as there was 2 to 3 inches between the XM antenna and the ferrite ring then everything was solid even if the GDL 39 unit antenna end was touching the XM antenna (as Steve noted).
I am sure the experts will be able to understand why this occurs but at least I know what the problem was and the systems were rock solid on the flight back.
I also tried the bluetooth connection which worked perfectly. Will be very cool when we get the ground stations working in Oklahoma to see the weather and traffic.
 
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