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shielded wires

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icubob(at)newnorth.net
Guest

Posted: Sat Jan 27, 2007 5:15 am Post subject: shielded wires

have used bobs illustrations and have done a good  job making pigtails and daisy chaining the shielded wires for my ptt switch. now  i notice the 2 wire shielded cable a little stiff to easily slip into my control  stick. wouldnt it work to attach the shield to my alum. control stick and then  use plain 22ga wire inside the stick? wont the stick act as the  shield?

   appreciate any input, bob  noffs

    [quote][b]

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nuckollsr(at)cox.net
Guest

Posted: Tue Jan 30, 2007 7:00 am Post subject: shielded wires

At 07:14 AM 1/27/2007 -0600, you wrote:

 	  Quote: 	
		  have used bobs illustrations and have done a good job making pigtails and 

daisy chaining the shielded wires for my ptt switch. now i notice the 2 

wire shielded cable a little stiff to easily slip into my control stick. 

wouldnt it work to attach the shield to my alum. control stick and then 

use plain 22ga wire inside the stick? wont the stick act as the shield?

   appreciate any input, bob noffs


	


   Bob, sorry for the delay on this. There's been a lot

   of conversation on the List recently and your inquiry

   moved a long way up the IN box . . .



   Sure . . . first, as I mentioned in another posting

   earlier, the vast majority of shielding called out in

   various drawings probably contributes nothing of electrical

   value in the typical small aircraft installation.



   This is because there are VERY few noise sources that

   propagate chiefly by electrostatic coupling . . . which

   is the form of firewall provided by shielding.



   I also confessed to using a lot of shielded wire as

   a convenience for quick-n-dirty multiple-conductor

   signal pathways in a bundle. I've got multi-thousand

   foot spools of single, twisted pair and twisted trio

   on the rack. If I need a trio for some task, I'm quite

   likely to grab a hunk of shielded than to build my own

   length of twisted wires.



   So, having confessed to all that, know that your suggestion

   for not taking the shields up the stick is a sound one but

   not for the reason you've guessed. It's not that the shielding

   is really useful but that it mostly likely doesn't matter.



                 -------------

                 <  CAUTION  >

                 -------------

    When installing a system wherein the

    instructions CALL OUT shielded wire,

    don't use this mini-dissertation to

    justify dumping shields unless you have

    a strong understanding of what those wires

    do an what the risks might be for electro-

    static noise ingress.



    All the LED annunicator fixtures I supply

    are wired with shielded wire as a fabrication

    convenience. See pages 10 and 11 of:



http://www.aeroelectric.com/articles/lvwarn/LVWarn-ABMM.pdf



    As I mentioned above, it's EASY to use

    shielded wire whether or not the shield

    is necessary . . . but it can be damned

    difficult to pull the new shielded wire

    in later. I've offered these words as

    enlightenment to the realities of shielding,

    not as a general recommendation to ignore

    the callouts on manufacturer's installation

    instructions.



    Bob . . .



        ----------------------------------------

        ( IF one aspires to be "world class",  )

        ( what ever you do must be exercised   )

        ( EVERY day . . .                      )

        (                  R. L. Nuckolls III  )

        ----------------------------------------

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