Wire shielding question

NYTOM · #1 03-04-2014, 02:12 PM

This may seem like a stupid question but here goes. Running they wire into the control stick for my PTT. There is also four push buttons for the trim system at the same location,plus A/P & frequency switches ( Ray Allen grip). Was going to use the common ground for the trim switch to also ground the PTT as per RA instructions. Would it be advantageous to shield the PTT and ground through the shielding instead of the trim common.With all the talk here about noise in the headsets from just about anything in the plane I'm getting paranoid about interference creeping into the wiring. Being part of the Pilots Mic wiring, wouldn't that long unshielded PTT wire running along with trim,flap,shielded led nav and strobe etc. pick up anything? My hearing is going south as it is and I need the keep it as quiet as I can. Any advice would be appreciated.

vlittle · #2 03-04-2014, 03:05 PM

Quote:

Originally Posted by NYTOM

This may seem like a stupid question but here goes. Running they wire into the control stick for my PTT. There is also four push buttons for the trim system at the same location,plus A/P & frequency switches ( Ray Allen grip). Was going to use the common ground for the trim switch to also ground the PTT as per RA instructions. Would it be advantageous to shield the PTT and ground through the shielding instead of the trim common.With all the talk here about noise in the headsets from just about anything in the plane I'm getting paranoid about interference creeping into the wiring. Being part of the Pilots Mic wiring, wouldn't that long unshielded PTT wire running along with trim,flap,shielded led nav and strobe etc. pick up anything? My hearing is going south as it is and I need the keep it as quiet as I can. Any advice would be appreciated.

Best to have a separate ground for the ptt. Use a two-wire shielded wire. Ground the shield and one wire at the intercom. Use the two wires inside the shield to connect the PTT. For 99% of the installations, this is overkill but it's easier to do it right.

NYTOM · #3 03-04-2014, 05:17 PM

Thank you Vern.

Overkill can be good sometimes. I thought this wiring job was going to be easy. Sometimes I feel like my heads going to explode.

longranger · #4 03-05-2014, 09:00 AM

+1 on Vern's answer. When you have a choice it's best to not have the shield carrying current, no matter how small.

NYTOM · #5 03-05-2014, 09:25 AM

What's your feelings on grounding one end of shield or both? I've read articles and talked to people supporting both ways with the majority saying to ground just one end to avoid making a loop. I just hate to get all these wires bundled up nice,neat and tight and then have to go back in and tear it apart looking for a noise in the audio system.

longranger · #6 03-05-2014, 09:31 AM

Short answer: ground the shield at the signal source equipment.

Long answer: http://www.vansairforce.com/communit...d.php?t=110408

NYTOM · #7 03-05-2014, 11:22 AM

Quote:

Originally Posted by longranger

Short answer: ground the shield at the signal source equipment.

Now that's the first time I have seen that. Makes perfect sense. I may get this thing flying yet!
Thank Miles

vlittle · #8 03-05-2014, 12:49 PM

See http://makerplane.org/forum/viewtopic.php?f=23&t=140
And http://makerplane.org/forum/viewtopic.php?f=23&t=144

These posts should provide some guidance. The issue with noise on music inputs is easy to solve. I reduced my noise level from 'annoying' to 'insignificant' on Ranter's Noise Interpretation Scale. ;-)

NYTOM · #9 03-05-2014, 03:15 PM

Outstanding links Vern. Just learned something about GPS noise I didn't even know existed. Boy am I happy I haven't installed the GPS yet. Seems like most of the equipment in my panel needs to share the GPS signal and if you hadn't posted I'd have one noisy cockpit.
I took a two day EAA electrical coarse and about the only thing it taught me was how to crimp connectors. I'm learning more important things from you guys in a few posts. I really do appreciate your help.