Wire Shielding EMI or RF Noise?

[Bryan Broaddus]

I've seen a few things I can't agree with on this thread. Just for a reference I have run an Electromagnetic Interference Test lab for the last 35 years or so and am a Certified EMI/EMC Engineer.

Solid wire is NOT as good a ground as stranded wire, Actually you should use 1/2 inch or larger braid for your ground straps. The stranded wire has more surface area which in turn leads to less inductance. Inductance is then enemy of a good ground. It opposes current flow and will develop a voltage across its impedance. Not good. You want the absolute lowest impedance you can get on your grounds.

Keep your grounds as short as possible. again this will limit the impedance of the ground and increase its effectiveness.

Too many units on a ground does NOT lead to R/F noise. If the ground is solid, like the negative battery post, then terminating all the returns there is a good idea. Now, if the ground you pick is a crappy ground and you stack up a bunch of devices on a bad ground then you can couple energy from one unit into the other via the ground.

The plastic clamp on Ferrite beads are a good idea on wires that you are afraid of coupling signals into. You can clamp then on the ends and even put a few on the wire spaced out evenly. This will not effect the desired signal on the wires but will soak up the unwanted RF energy that is coupling on the wires. Ferrites are much more effective on high impedance wires, like your tach lead but do not work much on low impedance leads like power wires. They can still have some effect but not nearly as much.

Shielded cable are only shielded if the ground is solid on both ends. In other words if the two units do not share a common ground then you may develop a voltage across the shield which can couple noise into the core wire under the shield.

You cannot ground something through an Anodized or painted case. So make sure to clean any anodizing or paint off of the area you are attaching the ground to.Clean bare metal is the best place to ground.

Adding extra grounds will not hurt you. So grounding the heads to the block and the block to the chassis is a good idea. Also for any ground you want a large CLEAN contact area. Threads, like through a bolt are notoriously bad grounds. You must rely on a large flat contact area.

[Dissident]

Mr. Broaddus,
I enjoyed your post. I wonder why more folks do not look at fabricating Faraday cages around either emitters or receivers to help defend against RFI/EMI problems. Your comments on grounds were spot on and unfortunately the average folks in the pits do not discern any difference in grounds accomplished by solid wires or braided cables. They are much more prone to apply whatever "bubble pack" solution might be at hand and most of those are boondoggles of one sort or another. Thanks for bringing some scientific methodology into the discussion.
Regards to All that like this kind of stuff,
HB2
Dissident