Carbon Fiber Sleeve For EMI Shielding?

[ggray]

I'm still trying to deal with the issue of shielding the new radar cable, and wondered whether a carbon fiber sleeve would work? I understand it would conduct electricity to some degree, but skeptical that it would shield against EMI.

I'd appreciate any help here!

[Stumble]

I really don't know, but I doubt it. CF conducts electricity, but not terribly well as a composite. There maybe CF tubes with copper sheathing payed into the laminate (they do this for CF airplanes) but I doubt it's particularly cost effective.

But aren't all radar cables shielded as manufactured? I suspect they don't need additional shielding past that.

[UNCIVILIZED]

Try googling electromagnetic cable shielding as a start. I'm sure there are plenty of pre-made, proven, cheaper options as compared to carbon fiber. Ones with built in isolating insulation, much as found in the construction of coax cabling.
electromagnetic cable shielding - Bing

[Paul L]

Why does your cable need added shielding over what is already built into the cable by the manufacturer?

[ggray]

Actually, a small carbon fiber sleeve is not very expensive, not much different from tinned copper braid, which I'm hesitant to use thinking there might be an issue with the aluminum mast.

The cable supplied is not shielded. t's just heavy duty USB wire. Garmin themselves suggested shielding if it is near the VHF cable, which it is.

It might not be a big deal. Other than Garmin, I'm really not finding much said about the problem, if any. However, it would be a lot easier to shield now than to find there is a problem, and have to do so later (which would require cutting a cable end off to get the cable out.

I was (and am) dubious of the CF shielding EMI, but it seemed like it was a reasonable question....

[Matt Johnson]

Typically, carbon fiber and aluminum is not a good idea. If the cf touches a non anodized, moist area of your mast, corrosion of the aluminum will start. Lots of other shielding options available.

Matt

[Jim Cate]

Actually, a small carbon fiber sleeve is not very expensive, not much different from tinned copper braid, which I'm hesitant to use thinking there might be an issue with the aluminum mast.

IIRC, carbon is a worse match on the electromotive scale than copper, so galvanic corrosion would still be an issue in an aluminium mast.

Jim

[Stumble]

Originally Posted by Jim Cate

IIRC, carbon is a worse match on the electromotive scale than copper, so galvanic corrosion would still be an issue in an aluminium mast.

Jim

Carbon is pretty much the most noble common material found on boats. There are some things higher up, but you probably won't see them. Stuf like certain platinum alloys...

So ya, putting it into direct contact with aluminium is a pretty bad idea.

[Wotname]

Originally Posted by ggray

..........

The cable supplied is not shielded. t's just heavy duty USB wire. Garmin themselves suggested shielding if it is near the VHF cable, which it is.

It might not be a big deal. Other than Garmin, I'm really not finding much said about the problem, if any. However, it would be a lot easier to shield now than to find there is a problem, and have to do so later (which would require cutting a cable end off to get the cable out.
....

EMI cable shielding is a science and to get it right, one needs to know a lot of things - frequencies, pulse rates, voltage levels are just the beginning. Throwing a off the shelf copper braid over it is pretty hit and miss approach. The fact that Garmin hasn't provided a properly designed shielded cable suggests to me that this might just be an ACE; inserted into the install manual by their corporate lawyers.

In the past (and I have been involved installing Garmin products since their inception - think GPS100 ), Garmin was always spot on with their installation advice and their stuff always worked as designed. These days, not so much. Their stuff is still good but not as good as it used to be. Some of the manuals appear to be written by coders rather designers...

If it was a real issue, they should be telling you how to shield their cable rather than leaving you guessing.

I agree that once it is pulled into the mast, you don't want to rip it out to rework the shielding etc.

Why not try to test it before running it in the mast. If the VHF coax is not yet in the mast, then lay the VHF coax and radar cable side by side and temporary tape together. Fit a temporary antenna (or fabricate one by stripping some of the braid off the end of the coax run - plenty of references around on how to do that) and fire up both the radar and the VHF and see what the issues really are. If the VHF coax is already installed then you might have to spring for another length of coax to carry out this test but it will either give you peace of mind or a good baseline in case you really have to shield the radar cable. This way you will know if the selected shielding method will work before it is fitted into the mast.

[Paul L]

I kind of doubt it is a USB cable. More likely an ethernet cable with a separate or combined power cable. Is there any chance you can run it in a different conduit to the VHF cable a few inches away? Either way, I doubt you will have any real issue.

[foufou]

If it is electro magnetic interference then the magnetic component of the interference needs to be addressed as well as the electrical component. That requires a magnetic material like steel as shielding

[a64pilot]

Carbon fiber will not work for RFI / EMI shielding, when it is used in aircraft, almost always there is a copper or aluminum wire mesh in the layup for shielding, and there has to be metal to metal contact with that shield to ground, just having the metal there is not enough.
You can buy inexpensive braided tinned shield, it is sort of like making your own co-ax.

But, what makes you think it needs shielding? I would be real surprised if it needs it and wasn't already

[meridian28]

If it's a Ethernet cable (cat5/6) you can buy it shielded. Contact a telephone/cable/IT company. They will have it or know where to get it.

[ggray]

Thanks for all the good information!

And BTW, this is what I'm trying to deal with, from the manual:

"To avoid interference with other equipment, network and power cables should not be run next to or parallel to other cables, such as radio antenna lines or power cables. If this is not possible, the cables should be shielded with metal conduit or a form of EMI shielding."

First off, I did mean ethernet cable, not USB. There is a separate power cable.

Second, that ethernet cable has large water-tight cable ends which I'm guessing are proprietary, so I will have to/want to stick with that.

Third, I found out today that the two cables (radar, and the VHF) have two separate conduits, and that they are aluminum, so it would seem that the only place of concern will be from the base of the mast to where the network cable and the VHF cable go their separate ways. I will probably put copper braid or aluminum foil around that part of the VHF cable. And as suggested, it would be easy to experiment at that location.

[Wotname]

Originally Posted by ggray

Thanks for all the good information!

And BTW, this is what I'm trying to deal with, from the manual:

"To avoid interference with other equipment, network and power cables should not be run next to or parallel to other cables, such as radio antenna lines or power cables. If this is not possible, the cables should be shielded with metal conduit or a form of EMI shielding."

First off, I did mean ethernet cable, not USB. There is a separate power cable.

Second, that ethernet cable has large water-tight cable ends which I'm guessing are proprietary, so I will have to/want to stick with that.

Third, I found out today that the two cables (radar, and the VHF) have two separate conduits, and that they are aluminum, so it would seem that the only place of concern will be from the base of the mast to where the network cable and the VHF cable go their separate ways. I will probably put copper braid or aluminum foil around that part of the VHF cable. And as suggested, it would be easy to experiment at that location.

A few points:

Low level EMI (which is what this issue is about) diminishes rapidly with separation and is also proportional to the length that the cables are close together. From your description, it does sound like this distance will be short so that is a good thing. If you do use copper braid, do make sure it is insulated from any contact with the aluminium.

The extract from the manual is a typical ACE but to give it due credit, it does at least alert one to the possible problems.

I recall being at a training course yonks ago run by a large avionics manufacturer and this subject was raised when considering how to install some of their very expensive collision avoidance technology. In essence it was impossible to comply with all the recommendations and still fit it into any know airframe. The instructor acknowledged the issue and explained that one must start with perfect practice and degrade that only enough to get the equipment installed. Each installation and each different airframe poses different challenges. After each installation, a full procedure of testing is carried out to test for EMI - either to the new equipment or existing equipment. If all is good, then the installation becomes "best" practice rather than perfect.

What you are currently facing is discovering what will become best practice in your circumstance. I'm sure it will work out for you; remember most folk don't even read the manual until something goes wrong .