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To: lml@lancaironline.net
Date: Sun, 23 Apr 2006 12:11:10 -0400
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From: "Tom Gourley" <tom.gourley@verizon.net>
Subject: Re: [LML] Re: Avionics=Black Art
Reply-to: "Tom Gourley" <tom.gourley@verizon.net>
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> So here's the real issue, I want to break these two cables(2  conductor 
> 22ga twisted pair with braided shield) with inline  connectors for ease of 
> installation.

Have you checked out www.digikey.com?  Maybe one of the circular metal 
connectors? You mentioned the wiring was shielded twisted pair.  Do you know 
what signals are on these wires?  If they're RS-232 or ARINC429 then we're 
not talking about fast signals, rf, or sensitive analog signals.  You could 
cut the twisted pair, add a wire and pin on the shield on each side of the 
cut (see http://www.aeroelectric.com/articles/pigtail/pigtail.html)  and 
carry the shield through the connector on a pin.  (An AMP CPC connector 
would be a good candidate for this.)  Or if the mating halves of the 
connector have metal bodies with a solid locking mechanism you could carry 
the shield through on the connector body.  I wouldn't recommend either of 
these methods if the signals are relying on the shield for impedance 
control, but I doubt they are.  Twisted pair will have a fairly consistent 
impedance between the two wires, and in any case it would be difficult to 
maintain a specific impedance between a wire and a shield.  Real impedance 
control requires coax or something similar.

Tom Gourley

----- Original Message ----- 
From: "Greenbacks, Ltd." <N4ZQ@comcast.net>
To: "Lancair Mailing List" <lml@lancaironline.net>
Sent: Saturday, April 22, 2006 9:22 AM
Subject: [LML] Re: Avionics=Black Art


> Back to the issue of shield grounding for a moment...
>
> The Apollo/UPSAT/Garmin AT install manual wiring diagram for the MX20 
> interface with a WX500 shows both the Tx and Rx cables having their 
> shields terminated at each end with connection to the chassis of each 
> unit. The WX500 install manual specifies that the shields be  terminated 
> at one end only:
> Tx grounded at the WX500 chassis and Rx grounded at the MX20 chassis.  I 
> haven't the foggiest notion of which one is the more elegant  solution but 
> I'm inclined to ground at both ends as per the MX20  manual since I do not 
> expect to build ground loops into my system. ):
>
> So here's the real issue, I want to break these two cables(2  conductor 
> 22ga twisted pair with braided shield) with inline  connectors for ease of 
> installation.
> I haven't been able to locate suitable connectors which will do the  job 
> and maintain the integrity of the shield. Any suggestions for a  connector 
> part #/manufacturer?
>
> Angier Ames
> N4ZQ
> N3ZQ
>
> --
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