asif2002

Hey guys,
I finally graduated yesterday and have the whole summer off. I am gonna start on installing my 99 Navigation unit on my non navi 00 TL. I got all the schematics from the electrical helms manual. The only concern I have is about the shielding. Where could I get some and how do I do it. There is a location from the Navigation Display Unit to the Navigation Unit that has to be shielded. In the bood it says RFI(Radio Frecuency Interface) I think It is to block out the static. If someone that knows could help me . THanx

Southbound

If you have the schematics then they should show you which cable or cables need to be shielded. They will usually be drawn with a wire or wires with a circle drawn around the bundle and a ground symbol used.

The shield is always connected to ground. It may be a static shield or a dynamic shield. If it's a static shield it is only connected to ground at one end and no actual current is being drawn through the shield (drain) wire. In a dynamic shield situation, the shield is connected at both ends and actually carrys the ground current between the two devices that it connects.

Typically, if you have only ONE signal wire, you will use a shielded coaxial cable with the shield connected at both ends. This is like video cable. Sometimes, in balanced audio or low level signal lines, there may be SEVERAL pairs of wires that need to be shielded. In that case, you will need to get some multiconductor shielded cable and connect the shield as per the schematic.

You can also buy simple braided shield that you can slip wires inside of and then use to shield the enclosed wires. In this case, you have to be careful to put some insulation over the ground braid so that it doesn't come into contact with some other connection and short it out to ground. Shrink tubing is good for this purpose. Sometimes your run may not be near anything to worry about and you can leave the braid exposed. You can also sheath it inside of those black corrugated wiring harness tubing sections that you see running all around your engine. But you shouldn't need to go this route. This is only if you have to make up your own "custom" shielded cable. You should be able to buy the cable you need already shielded.

SOOOOOOO, you need to find out how many wires you need to shield... then you need to go buy either a single coax cable (like video cable) or some multiconductor shielded cable. In multiconductor shielded cable, a lot of times there are individually shielded "Pairs" inside the overall shielded bundle. Or sometimes there are just a number of wires covered by a single shield. It's all a matter of what you need. You also need to know where to get it. Radio Shack will have video cable, but I'm not sure what they stock if you need something other than that.

Also, there are different kinds of shields. There is braided shielded cable, where a copper or aluminum "braid" actually surrounds the center conductor. Watch out for the CHEAP types of this coaxial cable. Some of the "hobby" brands are only shielded by like 50%. Then there is cable that has a "Foil" shield wrapped around the center conductor or the bundle of wires. Along the side of this foil, runs a "drain" wire that is touching the foil all the way through its run. So when you strip the cable, you simply peel back the foil and use the drain wire as your "SHIELD/GROUND" wire. With a braided shielded cable, you need to strip back the braid from the center conductor, strip the insulation off of the center conductor, twist the peeled back shield until it looks like a wire, and use these two wires for your connections. If you are butting coaxial cable to certain industry standard video type connectors, then the shield is crimped to the ground of the connector.

It sounds like you probably need a shielded coax if it's to feed your video display. You may need three if it's fed RGB. Then again, it's probably an SVGA computer monitor type connector, which has several shielded wires inside of it. If it's a single coax, it's probably a small type coax as compared to the typical RF/video cable that you are used to using for your TV antenna input at home. Belden RG174 is good for this type of use, but it's fragile and hard to work with for a novice. Larger video cable could be too cumbersome to work with behind the dash and could be stiff enough to break connectors, etc. Computer monitor cable may be the answer... you can strip this back and use it as your needs require. There is also double shielded cable and cable that is shielded with both foil and braid. The better the shield the better the RFI rejection and the better off you are. DON'T get the cheap stuff... Make them strip back the braid and show you that it covers 100% of the wire, not just a lattice network that covers 50%. Foil is actually ok to use because it does cover 100% of the wire, but it does become fragile after time and will break apart inside leaving lots of open areas. This is only a concern when the cable is being moved a lot like on a computer mouse or something... In a permanent strain relieved installation, I'd feel safe using foil shielded cable.

The purpose of using shielded cables is to keep cables that are carrying high frequency signals from "crosstalking" into adjacent cables. It is also used to keep sensitive low level signal wires from picking up RFI from other cables that are carrying significant amounts of RF or from picking it up by RF that is being radiated throughout the air by EMI effects, etc. Have you ever touched an unshielded microphone? The mic line is such a low level signal that just your hands and body will act like an antenna and radiate RF and 60cycle hum into the microphone. If you have unshielded cable running to your navigation video display, I'm pretty sure that you would see "beat" patterns in the video, like "herring bone" patterns and other wavy lines, etc. Also, the CD player and radio will be picking up this RFI information and try to reproduce it with many annoying sounds.

Talk to somebody at an electronic supply Ham Radio type store about what you are doing and show them the schematic. Some of these guys have no-life and just love to show you how to do it right.

Good luck!
Southbound

asif2002

Damn Bro,
I've been here for like 30 min just trying to read it. Thank you for helping me out with this. I think this should be a thread that would be very useful. Thanx again. Ill post the Schematice for it. YOur the man