SkyView Interference (EMI) with Garmin 796 GPS

[rswalden]

I have dual SkyView 10" displays with a Garmin 796 GPS mounted sideways (landscape orientation) between the two units.   This places the internal antenna of the 796 within 3 inches of the SkyView.

Even though I have an external GPS antenna attached to the Garmin 796, its internal antenna receives an enormous amount of interference from the SkyView unit and I lose GPS lock on the 796 repeatedly in flight.

My only solution when this happens is the TURN OFF the SkyView until the Garmin has regained enough signal strength the come back on line.

I've talked with Garmin, and there is no way at present to inhibit its internal antenna.

Can you Dynon experts suggest any way to reduce the EMI from your SkyView display?

Also, when I DO turn off the SkyView in flight by pressing the on/off left button...  I cannot turn it back on using the same button, and have to cycle my main battery power switch.    My backup battery checks ok, so that's not the issue.

Any help you or others can give me is greatly appreciated.

 

[dynonsupport]

I'll admit that I'm not an RF engineer, but I can't see how you can have two antennas active at once. Every GPS I have seen, when you plug in an external antenna, it disables the internal one with a mechanical switch triggered by plugging in the external one. Having both antennas working at once is really not possible with a GPS. If one GPS antenna is in the panel and another was out on the wing, what position are you at since GPS determines position via where the antenna is and a GPS is easily sensitive to 10 or 15 feet? Two GPS antennas is like a man with two watches...

I think you first need to test and see if the external antenna is working. Turn off SkyView, and let the Garmin get a lock. Go to the satellite status page on the Garmin and put your hand over the external antenna. You should get a strong drop in signal strength. If you don't, I think you have an external antenna problem and should solve that.

If it does work, then you are likely getting interference into the external antenna cable or the antenna itself. First test is to see if both SkyView screens cause a problem. Do the same satellite status page check as you turn on and off each SkyView and see if one or both are the issue.

Try re-routing the GPS antenna cable as far away as possible from any SkyView wiring harness, and if you have extra cable on the antenna, make sure that it's not wrapped around any cables.

Also, where is your external Garmin antenna and how far away from the SkyView screens? Any extra distance you can get there will help.

As for turning on with button 1, are you holding it for about 3 seconds until the screen lights up? It doesn't just turn on with a tap.

 

[rswalden]

Mark,

Thanks for the reply.
Garmin confirms that my 796's internal antenna is always active, even with the external mini-jack to the remote antenna connected. They are looking at the possibility of a user-inhibit function on a future firmware release. My Garmin antenna is located 10 feet away from the unit, next to the SkyView antenna. I've even tested the unit with a new remote antenna in a different location.

There's no question that the SkyView display is generating enough EMI to the Garmin 796 to weaken the signal strength.

I'm not putting the blame on Dynon for the interference. The Garmin 796 internal antenna being always active is a bad design.

Thanks for your comments... Just thought I'd make others aware of potential problems with that unit.

 

[rswalden]

Mark:  A video is worth a thousand replies.....
http://youtu.be/8zpb_hwUIfQ

This video begins with a shot of the 796 GPS satellite "green bars" showing weak signal.  When the SkyView unit is turned off, the 796 immediately shows improved signal strength. 

This is a DESIGN flaw in the Garmin 796 that uses its INTERNAL antenna, even though an external antenna is attached.   My 796 is mounted sideways (landscape mode) that places its internal antenna just inches away from my Dynon Skyview, resulting in electromagnetic interference.  Garmin needs to have a way to inhibit the 796 internal antenna when an external antenna is attached.

Note also a bug in my SkyView system.  It can only be turned back on by cycling the battery switch... the power button on the SkyView doesn't respond, even when held for 20 seconds.   As soon as the SkyView boots up, signal strength in the 796 immediately drops.

 

[dynonsupport]

The bug where SkyView does not turn on with button 1 is fixed in software release 6.2, which was released a few days ago.

 

[rodpump]

Mark,

I also have a 796 in conjunction with the Skyview system mounted further away & in the portrait mode. I'm able to receive the gps signals with no problem. How about mounting a lead shield between the Dynon & the 796. That might block the emi. Just a thought, don't know if it will work. Good luck!

Don

 

[maartenversteeg]

Don,

Please note that while lead is a good nuclear radiation shield, it doesn't do much with respect to electromagnetic fields. A magnetic soft metal (mu-metal) shield would do much more for magnetic fields, and any conductive shield stops electrical fields. But note that EMI radiation is not very directional, so normally units have to be completely enclosed to ensure that no EMI/EMC radiation can come out or in, with display units this is already impractical. In most cases careful grounding of housing will help a lot.

- Maarten

 

[rswalden]

Attention DYNON SUPPORT

You can delete this post entirely that I posted.

The issue has been SOLVED.

My Garmin 796 external antenna jack was DEFECTIVE, rendering the external antenna inop.  Garmin Tech Support  sent me a replacement 796 unit, and it works great.  Yes, the Dynon SkyView units DO generate EMI signals that blank the Garmin 796 internal antenna.  But a good external antenna for the 796 solves the problem.

By the way:  to YOUR (Dynon's) credit, the SkyView GPS antenna has always worked without ever dropping its signal.  Great system you have....

 

[Dynon]

I think we may want to keep this thread around for posterity for when someone mis-remembers history of the issue here or over on other forums . But we're thrilled that you got the issue solved. We touched base behind the scenes with some of the engineers at Garmin, and we were both equally puzzled on this issue. Since your experience just didn't jive with others in similar configurations, we didn't think that the SV was blasting the world with abnormally high levels of interference. Thanks for closing the loop here too!

 

[richardg]

Does the Dynon Skyview need an external GPS aerial or can it be mounted internally?

 

[dynonsupport]

The GPS antenna needs a clear view of the sky, without anything to block RF. It can see through most plastics, so some people do install them inside the canopy area. In my plane, it's inside looking though the fiberglass fuselage.

 

[richardg]

Thanks for your reply

 

[richardg]

Skyview and transponder

I understand there has been a problem with firmware between dynon (TRI) transponder and Skyview. Just want to check this is sorted before fitting mine. Otherwise will fit separate head.

 

[dynonsupport]

We're not aware of any issues with our interface with our transponder.