reducing noise, shielding EMI

**hateeecs** · 09-06-2005, 11:30 AM

Hello all,

I have a few EMI issues in my setup and was wondering if I could get some advice.

My current setup is as follows:
- battery, ignition switched 12V and ground on drivers side
- ground and 12V from PSU running on drivers side to my screen
- RCA on passenger side
- VGA, USB running down the middle
- computer is in the trunk in a wooden case

I'm noticing some EMI that i think is mainly being caused by the 12V line that I have running to my screen. I say this because as I move these wires around on my dash the radio reception varies from ok to bad.

So what to do:

Here are a few things I have though of but not yet tried and was wondering if anyone can comment.

- twisting ground and 12V around like twisted pair ethernet. From what I have read this will not help much
- using tin foil and soldering that to ground
- slipping a braid over the wires (i have not actually found a store for this)

Any comments or other ideas on how I might shore this up?

Thanks,
-Chris

**greenwire** · 09-07-2005, 01:38 PM

That sounds more like a loose connection somewhere than EMI issues, but you could try checking for ground loops and shielding everything.

Shielding everything is a pain in the ***, and can get quite expensive if you use the proper metal sheathing, just use tin foil but don't short anything out

**lexanite** · 09-08-2005, 07:58 AM

Seem that you make a ground loop connection from three points. The driver side, the PC, and the Screen.
Please reroute the power supply for your Screen. Remove from the driver side and take the 12vdc fron the PC side. So at the end, the power wire should be from the driver side -------- PC in the trunk ------- Screen.
Hope can solve.

**hateeecs** · 09-08-2005, 09:14 AM

Originally Posted by lexanite

Seem that you make a ground loop connection from three points. The driver side, the PC, and the Screen.
Please reroute the power supply for your Screen. Remove from the driver side and take the 12vdc fron the PC side. So at the end, the power wire should be from the driver side -------- PC in the trunk ------- Screen.
Hope can solve.

I'm a bit confused. Currently, I'm running 12V+, 12V ignition switched, ground to the PC on the drivers side. This is all for the computer. Then on the same side I've run 12V and ground from the molex connector on my PSU.

So all these wires are on the driver side.....hrm....

Maybe i'll just try running the screen power down the middle of the car. This seemed to be far less of an issue when I was simply using the cig lighter to power the screen.

**lexanite** · 09-08-2005, 11:30 PM

Originally Posted by hateeecs

I'm a bit confused. Currently, I'm running 12V+, 12V ignition switched, ground to the PC on the drivers side. This is all for the computer. Then on the same side I've run 12V and ground from the molex connector on my PSU.

So all these wires are on the driver side.....hrm....

Maybe i'll just try running the screen power down the middle of the car. This seemed to be far less of an issue when I was simply using the cig lighter to power the screen.

Your VGA cable also make a ground connection within PC and Screen. Thats why you must reroute your Screen power, not to make any ground connection to the Driver side (create the loop). If you move the power wire for the Screen to the PC, you break the LOOP in the same way. Take the power for the Screen from PC side, try the same length with the VGA cable.