MGL Avionics User Forum

I have a challenger lite as PFD and a Garmin 795 with GDL50 as backup on right side. Vans RV7. I can switch autopilot sources betwen MGL and garmin.
Increasingly i find the 795 unable to receive a usable GPS signal while the Challenger is operating. Challenger is fine, shows plenty of GPS signal even inside a metal hangar.
But the garmin satellite signal page shows the bars dropping to zero when i switch on the MGL. Evrything points to emitted MGL screen radiation killing the garmin GPS capability. I can map the cockpit with the garmin, watching satellite signals shrink or grow depending on position and on proximity to the MGL screen. And this is all on the ground, where i cant blame other interference sources. After 10 minutes in the air i often get a usable garmin GPS signal, but it can take a while.
The worst location is when the garmin is in the panel mount, making me wonder if something else is interfering . However the problem persists even with all other electronics shut off, and moreover with the garmin in battery mode !
I have foil wrapped garmin , taken earth back to main battery, put ferrites everywhere i can think of, electrolytics on powerlines. Using G3 most recent OS, D 1.1.2.3. . Aluminium foil behind and in front of screen. Doesnt help. Borrowed garmin behaves exactly the same.
The problem is MGL screen radiating. I cant seem to sort it out. Getting frustrated.
Interested in suggestions.
Is there a less radiant screen option??

Highly unlikely that the EFIS screen would affect the GPS signal.

However - the most common issue if you have multiple GPS systems is interference between antennas. This is because many external antennas are active antennas meaning they have built in amplifiers. The amplified signal with have time and phase differences to the original received signal and will leak out of the antenna cable as well as the antenna itself. This is then received by other GPS antennas.

The effect falls with distance - normally you only have issues if the antennas (or cables) are fairly close to each other - but I have seen occasional issues with them as much as a meter apart.

The GPS in our EFIS is a u-blox - this has very good anti-jamming and interference performance. Many other GPS systems - in particular those that have their own built in or side mounted antennas are passive in nature as there is no need to cater for cable losses (which at 1.5Ghz are considerable) - but they tend to be more sensitive to interference.

So in a nutshell - the first thing I would do in your case is simply unscrew the GPS from our EFIS (at the rear or iBOX depending on what you are using). If that fixes the issue you have your answer. Reroute the cable and GPS antenna itself to a better position.

If it's the screen radiating (again, there is nothing being radiated here that can reach to these kind of frequencies) - it would also affect the GPS signal of the EFIS so you can even use the supplied GPS antenna as probe.