X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Sat, 22 Apr 2006 17:16:12 -0400 Message-ID: X-Original-Return-Path: Received: from mta10.srv.hcvlny.cv.net ([167.206.4.205] verified) by logan.com (CommuniGate Pro SMTP 5.0.9) with ESMTP id 1076787 for lml@lancaironline.net; Sat, 22 Apr 2006 13:18:08 -0400 Received-SPF: none receiver=logan.com; client-ip=167.206.4.205; envelope-from=Adam@ValidationPartners.com Received: from VpiWorkstation1 (ool-45704ccc.dyn.optonline.net [69.112.76.204]) by mta10.srv.hcvlny.cv.net (Sun Java System Messaging Server 6.2-4.03 (built Sep 22 2005)) with ESMTP id <0IY40088LW0V0F5Z@mta10.srv.hcvlny.cv.net> for lml@lancaironline.net; Sat, 22 Apr 2006 13:17:20 -0400 (EDT) X-Original-Date: Sat, 22 Apr 2006 13:17:22 -0400 From: Adam Molny Subject: RE: [LML] Re: Avionics=Black Art In-reply-to: X-Original-To: 'Lancair Mailing List' X-Original-Message-id: <0IY40088MW0V0F5Z@mta10.srv.hcvlny.cv.net> MIME-version: 1.0 X-MIMEOLE: Produced By Microsoft MimeOLE V6.00.2900.2869 X-Mailer: Microsoft Office Outlook, Build 11.0.5510 Content-type: multipart/alternative; boundary="Boundary_(ID_GxQoKlEsP4VYJ5sNrbpfgg)" Thread-index: AcZmHRyEncnIpyzxRzSRasdLX8eDJQAA2yNQ This is a multi-part message in MIME format. --Boundary_(ID_GxQoKlEsP4VYJ5sNrbpfgg) Content-type: text/plain; charset=us-ascii Content-transfer-encoding: 7BIT Hamid - >If you are going to terminate a shield in a wire that goes into a pin, you >are wasting your effort. The wire and the pin is going to have a high >enough impedance at high frequencies to be rendered totally useless. Can you quantify those high frequencies? The wire termination is supposed to be no more that 2" long. To what frequencies will it be susceptible? >A single terminated shield does provide protection against ground loops >created by poor wring or poorly designed avionics. Isn't a double terminated shield the definition of a ground loop? >There is only one way to terminate a shield: >To the back-shell of a properly grounded connector. Unfortunately you >are SOL if the idiot designing the avionics does not know about proper >grounding. Meaning that if the avionics designer does not provide a grounded connector body or uses a connector that does not have a groundable >backshell available. This sounds like PS Engineering. Their backshell is plastic, and their installation manual states that all the shields are to be single-terminated by daisy-chaining them together and connecting them to the ground pin on the DB25 connector. Is their installation manual wrong? http://www.ps-engineering.com/docs/PM3000_IM.pdf Bob Nuckolls' Aeroelectric website has an article describing how to terminate shielded cable. Is his method incorrect? http://www.aeroelectric.com/articles/pigtail/pigtail.html Adam Molny Lancair #151 --Boundary_(ID_GxQoKlEsP4VYJ5sNrbpfgg) Content-type: text/html; charset=us-ascii Content-transfer-encoding: 7BIT

Hamid -

>If you are going to terminate a shield in a wire that goes into a pin, you >are wasting your effort. The wire and the pin is going to have a high >enough impedance at high frequencies to be rendered totally useless.

Can you quantify those high frequencies? The wire termination is supposed to be no more that 2" long. To what frequencies will it be susceptible?

>A single terminated shield does provide protection against ground loops >created by poor wring or poorly designed avionics.

Isn't a double terminated shield the definition of a ground loop?

>There is only one way to terminate a shield:

>To the back-shell of a properly grounded connector. Unfortunately you

>are SOL if the idiot designing the avionics does not know about proper >grounding. Meaning that if the avionics designer does not provide a grounded connector body or uses a connector that does not have a groundable >backshell available.

This sounds like PS Engineering. Their backshell is plastic, and their installation manual states that all the shields are to be single-terminated by daisy-chaining them together and connecting them to the ground pin on the DB25 connector. Is their installation manual wrong?

http://www.ps-engineering.com/docs/PM3000_IM.pdf

Bob Nuckolls' Aeroelectric website has an article describing how to terminate shielded cable. Is his method incorrect?

http://www.aeroelectric.com/articles/pigtail/pigtail.html

Adam Molny

Lancair #151

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