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Stupid question I'm sure

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aadamson(at)highrf.com
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Posted: Fri Jun 15, 2007 12:54 pm Post subject: Stupid question I'm sure

Ok, so in a composite airplane.  As it relates to the Radio Stack.  The

Radios, Audio panel, etc are mounted in an aluminum chassis, and some of the

items have "shield" that go to the outer tabs on the radios, etc.  So do I

need to take a ground from the radio rack chassis to the single point ground

of the rest of the airplane?  Or do those "Shields" end up being grounded

back thru the ground wires to the radios themselves?



Hope I explained this well enough to get a response?



Alan

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nuckollsr(at)cox.net
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Posted: Sun Jun 17, 2007 5:55 am Post subject: Stupid question I'm sure

At 04:53 PM 6/15/2007 -0400, you wrote:



 	  Quote: 	
		  

<aadamson(at)highrf.com>



Ok, so in a composite airplane.  As it relates to the Radio Stack.  The

Radios, Audio panel, etc are mounted in an aluminum chassis, and some of the

items have "shield" that go to the outer tabs on the radios, etc.


	


    Not sure what "shields" you're referring to or what the "outer tabs"

    are.



 	  Quote: 	
		     So do I

need to take a ground from the radio rack chassis to the single point ground

of the rest of the airplane?  Or do those "Shields" end up being grounded

back thru the ground wires to the radios themselves?


	


   Assuming you're talking about enclosure components

   of the radios and not wiring, you will find that most

   if not all of your radios take the power (-) lead to

   the chassis internally. By the time all the radios

   get power grounded to the single point ground, the "stack"

   is pretty well tied down by multiple conductors. Additional

   wires from the stack structure to ground will not add

   value.



   As for the shields on wires. Wire per the wiring diagrams/

   instructions for each radio.



   Bob . . .

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aadamson(at)highrf.com
Guest

Posted: Sun Jun 17, 2007 7:01 am Post subject: Stupid question I'm sure

Bob,



Thanks for the comments.  To be a little clearer.



I'm specifically wondering about the shields on shielded wires that connect

to the radios.  For example on the Garmin sl30, there are shields on wires

that connect the sl30 to the audio panel and those shields are attached

(only terminated on the radio side) to a metal extension plate that is

physically attached to the back of the sl30's mounting tray, which should

also attach it to the "chassis" of the sl30.



It is also my understanding that it most modern electronics, the manufacture

isolates the "chassis" from the internal power ground to prevent any form of

"short" that may harm a human.  If this is the case, then those shields

would not have a path to ground thru the chassis to the power ground.

Perhaps this assumption is incorrect.  I suppose I could tell by taking an

ohm reading off the ground lead to the chassis for example.  If they are

somehow connected, I should see a dead short correct?



In a metal airplane, this probably isn't as much of an issue as the radio

stack would most likely be chassis grounded thru the metal structure of the

airframe, but in composites, on in a composite panel, you don't have that

benefit and so I was curious if a separate ground wire should ground the

radio chassis to the single point ground?



Thanks,

Alan



--

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bobf(at)feldtman.com
Guest

Posted: Sun Jun 17, 2007 7:09 am Post subject: Stupid question I'm sure

I'd say you can't have too many grounds! the central point is key. You must be refering to the coaxial cable outer conductor (shield).... my question is should we pop a ferrite bead RF surpressor around the power and/or audio cable bundles out of the back of the radio to help ignintion noise surpression? 



bobf

W5RF



On 6/17/07, Robert L. Nuckolls, III <nuckollsr(at)cox.net (nuckollsr(at)cox.net)> wrote:[quote] --> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckollsr(at)cox.net (nuckollsr(at)cox.net)>



At 04:53 PM 6/15/2007 -0400, you wrote:



 	  Quote: 	
		  --> AeroElectric-List message posted by: "Alan K. Adamson" 

<aadamson(at)highrf.com (aadamson(at)highrf.com)>



Ok, so in a composite airplane.  As it relates to the Radio Stack.  The

Radios, Audio panel, etc are mounted in an aluminum chassis, and some of the 

items have "shield" that go to the outer tabs on the radios, etc.


	


    Not sure what "shields" you're referring to or what the "outer tabs"

    are.



 	  Quote: 	
		     So do I 

need to take a ground from the radio rack chassis to the single point ground

of the rest of the airplane?  Or do those "Shields" end up being grounded

back thru the ground wires to the radios themselves? 


	


   Assuming you're talking about enclosure components

   of the radios and not wiring, you will find that most

   if not all of your radios take the power (-) lead to

   the chassis internally. By the time all the radios 

   get power grounded to the single point ground, the "stack"

   is pretty well tied down by multiple conductors. Additional

   wires from the stack structure to ground will not add

   value.



 

[b]

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