Radio Transmit Screws up EFIS

[RayJr]

Hello,

I'm early in my investigation and was wondering if anyone had a hint which road to go down first.

When I transmit on my Bendix King 125, my MGL XTreme EFIS acts weird. If the transmit is long enough, it might restart or freeze. Shorter transmits will cause the temperate readings to go haywire.

I suspected a ground loop and insulated my headphone jacks (which were attached directly to the metal panel). But that didn't help.

I'm trying to track down a wire diagram for my KX 125 but so far no luck. They're physically close together, but I doubt that's related.

Anyone see something like this before?

 

[BobTurner]

I’d start by tracing the temperature (egt?cht?oat? You didn’t specify) wires, see if they are anywhere near the transmitter coax or antenna. If so, move and or shield them. Take a good look at the antenna and coax, make sure all connections to the ground plane (skin, most likely) are clean, corrosion free.

 

[RayJr]

Thanks Bob, The OAT temp is the one that goes wild first, indicating -85C or so on every transmit. I will give this a try. Cheers

 

[erich weaver]

Do you have any wires connected to the EFIS that are unconnected on the other end? Disconnect them from the EFIS. They may be acting as an antenna and picking up radio transmission interference that’s causing your problem.

 

[RayJr]

Do you have any wires connected to the EFIS that are unconnected on the other end? Disconnect them from the EFIS. They may be acting as an antenna and picking up radio transmission interference that’s causing your problem.

Thanks, I will check that too

 

[penguin]

What you are experiencing is not that unusual, the transmitted energy from the radio is being received by something connected to the EFIS and swamping it. I second the advice above. The receiver must be close to the length of a radio antenna (around 1.15m / 3.8ft or half of that). Also look for breaks in the shielding from the radio antenna coax. Are any wires bundled with the radio coax? If so separate them. Yes, the 2 boxes being close together is a factor. Its fundamentally a problem within the EFIS but you can do a lot to help out as I guess you don't want to replace it!