How to avoid electrical Ground Loops in Experimental Aircraft
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- Опубліковано 3 вер 2017
- This video demonstrates the cause and remedy of ground loops that can plague the communication radio reception in homebuilt aircraft. Electrical ground loops can cause noise in the receive audio of headsets and eliminating one cause of this noise is proper wiring of aircraft devices.
So very true. In times long gone, the early B-737 aircraft had the cockpit observer's audio jack located on an aluminum box next to the jump seat. The jack was insulated from the box by a phenolic insert. Inevitably, the insert would be broken by flight bags or feet entering the cockpit. Occasionally, some well-intended mechanic would fabricate a replacement insert from aluminum and install it because A, he did not have a spare on hand, and B, he was by god fixing it so it would not break again. Soon after, the crew would report noise on the interphone, and the avionics type would have to fix it. They knew where to look for the source of the problem.
You can speed this up to 1.5x in lieu of heavy medication, or... here's the shortest version: to protect against RF energy/interference, land the drain wire for cable shielding at ONLY one end - the other needs to be unconnected and insulated [drain wires do not come with insulation, as they must have contact with foil wrapping or mesh inside cable sheath]. The jack in this example uses an insulated conductor, which should tip us off that if there is a reference to chassis, it ought to be at a central point, not at the end device. Of note: COMmon [for various amplification setups] is not necessarily chassis ground - don't tie the two together [unless indicated]... but if you're that deep, you probably already have schematics in hand.
I have a Cessna 182 that had extensive avionics and radio replacements. I am getting some serious alternator noise through my headsets. The noise is now worse just after an install of a couple Garmin G5's. My Avionics shop said I need to replace the Alternator and regulator and if that doesn't help my problem I should bring the plane to him to trace down the problem. I know throwing parts at it is one way of doing it but not the way I want to go about it. Can a ground loop pick up this alternator noise? I plan to put my electrical system on an oscilloscope to check Alternator Ripple and make sure I don't have a bad diode but I really don't think that is the problem. Any thoughts that could help me trace this issue down? The video was very easy to understand and I am going to take a look at my communication jacks to make sure they are not grounded to where they are mounted to as well.
Jon, I find the way you talk gentle, precise and it helps me understand better the point you want to make. I enjoy your videos, the way you make them and the lessons that they carry. Thank you so much for all your efforts.
After trying to run down my problem, and talking with even the manufacturer, no one offered this solution to me. Months of struggles were simply solved by watching this video. I guess the solution was so simple that no one though to bring it up, Thank you
Just don't connect the shield to the headset jacks at all, only connect it to ground on the radio end. That is what the install manual that came with my radio said to do.
Every video I see from this guy seems to be a video designed for an elementary student. I'm not talking about the information; I'm talking about the presentation.
Considering I'm planning an all composite build, this gave me food for thought about how I'll need to go about creating good grounds while simultaneously preventing galvanism between the carbon fiber and wiring fixtures, jacks and plugs.
Love this guy. Explains everything with easy to understand instructions.
Thank you for sharing this great video.
Blimey I've been a radar engineer for years and dabbled with homebuilds and no publication has explained ground loops aswell as this!!!
Great video! You reduced the problem to a simple diagram to make it much easier to see the issue AND the solution. Kudos also to James Wills for his suggestion of fiber washers with a shoulder to positively isolate the ground braid on the microphone/earphone plugs.
Great videos Jon. You are my go to guy when I need some help (on par with "EAA hints for homebuilders"). Your instruction provides the rationale (which is why we build) as well as the "how to". At first I was taken back by the Mr. Fred Rogers slow pace delivery, but when I set the playback speed to 1.25 speed it is no longer an issue. Don't change a thing.
Such an awesome and thorough explanation. Thank you!
I’m not sure about experimental installations. However, STC installation manuals for stereo phones or mic audio/key cables use a 3-wire shielded wire and the shield is grounded ONLY at the Audiopanel. DO NOT use the shield as an audio low/return or ground line.
Simple, yet informative...well done.
Fantastic video, after installing strobe lights to my common ground (cigaret lighter plug) all looked like working great ....ready for flying next day ...but horrible static noise just from intercom no radio attached.
Great tip, Jon. Thanks again!
Excellent. I had a new audio panel installed in my Cessna 182 by a certified installer. Horrific engine noise! They were no help, so I began going through the installation manuals, which emphasized that the ground braids for the 4 mic/phone plugs should be grounded at ONLY ONE END (at the radio), NEVER BOTH. To accomplish this, the jacks were to be installed with two-piece fiber washers which had a shoulder that protruded through the mounting holes so they didn't make electrical contact.
that was really fun and educational to watch! thanks!