Grounds and Ground Loops

All,

I have a question concerning ground loops. I am presently installing a King KT76A transponder and an Odyssey EFIS/EMS. There are instructions to connect one or two ground wires between the two units and there are several ground wires on the plugs of the transponder as well as the EFIS - three on the transponder and four I believe on the EFIS. Does each ground need to be taken to a central firewall grounding point I am providing for the panel installed equipment or can grounds as they leave the connecting plugs be combined into a single wire to continue to the central location. If I understand ground loops correctly each of those ground wires is electrically connected within each instrument as well as throughout the airframe in general and therefore would/could cause ground loops if parallel grounding routes be created to the central grounding point. Combining the ground wires close to the unit would not eliminate the loops, but they would be considerably smaller. Old hands, which should I do?

Thanks! Cliff

You failed to mention if you are building a tail wheel model or a trike. Tail wheel models are more prone to ground loops than a trike.

I think what we have here is a failure to communicate.

Hi Cliff,

In my experience, all the ground that you mention can pretty much be tied in daisy-chain fashion, or run to a central panel ground (I do it both ways). the place where you have to watch out for ground loops is going to be in the audio system, and for that, you want to run things exactly as the appropriate manuals and drawings indicate, specifically at which ends the audio shields are connected.

Paul

don't think you have a problem groundlooping..... at least not now

I respectfully disagree Norman!! It is apparent that groundlooping can occur in aircraft on training wheels as well. However that aside which way are you wiring your Transponder Grey or Serial? I would assume you are using parallel as you failed to mention shielding. I installed serial initially on my MGL Odyssee, and after every attempt could not get it too work, so ended going the parallel route, and it works fine. I believe I only used one wire for grounding the units together, and one wire out of the efis and transponder to a common airframe ground. It all works great to date.

Jarvis,

Just for starters there is no difference between 'Grey' code and parallel for 'Grey' code is sent out as a parallel signal. The MGL products, if you read the manual, only output parallel Grey code, the serial ports can't be configured for altitude output.

As for ground loops try to keep audio grounds and digital seperate, that is not on the same common point. All HP and mike shields must not be connected at the HP and mike connectors, that is keep them floating. Only connect the shields at the audio panel, if you have one, else connect them at the comm radio.

The proper selection of high quality shielded wire and coax will generally eliminate most ground loop ane EMI/RF problems. The panel in my RV9 is full digital and there is no EMI/RF noise, actually I have to break the squelch to be sure the radios are working

John Higgins
RV9 N194JH

You are right John. I meant to say serial or grey not parallel or gray.

However yes the Odyssee does put out serial Data that a transponder is supposed to recognize in icarus format. It is in one of the manuals somewhere, and was confirmed from Matt (technical support), and that is why it is in the setup menus of the oddyssee. Just so you know.