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Bulent Aliev wrote:
Well, I just came from the hangar, 9PM and have not made any progress. Tried everything suggested. Disconnected the radio/AP grounds and run them directly to the battery - same problem
Opened the AP and extra grounded the unit - Nada
Everything that can make noise is making it?
Capacitors as suggested by Chad, did not make any difference.
I'll have to sleep on it. Too tired and frustrated.
Sorry, Buly, but I warned you it was probably a ground loop, and the caps wouldn't help. =) Because it's almost certainly a ground loop at this point, I wouldn't bother with chokes or other filters. A choke would have been a good next step if you noticed ANY reduction in the noise with the caps, since it's a more effective filter. But it won't do anything for a ground loop.
It's worth trying a radio swap, but I doubt it's actually going to help.
Also, if you can get a handheld that accepts an external antenna, it's still worth trying a device that can run on batteries. It'd be a useful data point in your report.
We'd really need a complete physical wiring diagram to help you identify the source of the ground loop, but if you're willing to do a bit more wire-rat work, I can suggest some basic things to try.
The MOST LIKELY source of a ground loop is anywhere you have:
1. Two audio devices connected together via a signal cable.
2. Your longest runs of signal wire between devices with individual grounds.
I believe you've ruled out an audio panel, but if you haven't you should connect your mic/headset directly to your radio for a test, completely disconnecting all other devices hooked to the radio. If the noise stays, that rules out #1. This is actually a good thing, believe it or not. You want that noise to stay there. If it goes away you'll have to figure out why you're getting an audio-signal ground loop and fix it, which is annoying, or try to work out some type of isolation transformer between the devices, also annoying.
Next, I'm assuming your engine sensors hook up to one or more engine monitoring devices. The engine, of course, is grounded, and any powered engine monitors (including the EC2/EM2 if you're using Tracey's stuff) will be grounded at the instrument panel. Change that. Grab a length of spare, thick hookup wire, and run it around from a screw terminal on your engine block (preferably right at its ground strap) around the outside of the plane to your instrument panel. No need for a permanent install right now. This gives you a direct engine ground.
Now, disconnect the ground for EVERY device that runs back to your engine. Any device you can live without, disconnect entirely. Anything you need to monitor (or run) the engine for the test, connect to the new engine ground. Try that.
Also, do you use a metal or plastic fuel filter? Determine whether your fuel pumps can be creating a virtual ground (if you have a completely-metal path from the pumps to the rail). If so, connect THEIR grounds to the new engine ground.
This process takes time, but it will be like flipping a light switch. If it's one of these devices, when you find the culprit the noise will just immediately go away. You can then isolate their grounds with individual firewall feeds and your noise should stay gone.
If this STILL doesn't work, then I'm out of ideas and would need to see a wiring diagram to take this further. (Or you missed a device - go over everything twice.)
Regards,
Chad
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