X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Sun, 16 Apr 2006 11:06:12 -0400 Message-ID: X-Original-Return-Path: Received: from [204.13.112.10] (HELO mail1.hometel.com) by logan.com (CommuniGate Pro SMTP 5.0.9) with ESMTPS id 1069942 for lml@lancaironline.net; Sun, 16 Apr 2006 09:22:13 -0400 Received-SPF: none receiver=logan.com; client-ip=204.13.112.10; envelope-from=marknlisa@hometel.com Received: (qmail 14095 invoked by uid 90); 16 Apr 2006 13:23:39 -0000 Received: from dsl-stj-204-13-118-2.stj.hometel.com (HELO MARKNLISA) (204.13.118.2) by mail.hometel.com with SMTP; 16 Apr 2006 13:23:39 -0000 From: "Mark & Lisa" X-Original-To: "Lancair Mailing List" X-Original-Cc: Subject: RE: Avionics=Black Art X-Original-Date: Sun, 16 Apr 2006 08:22:02 -0500 X-Original-Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook IMO, Build 9.0.6604 (9.0.2911.0) Importance: Normal X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1506 Angier, Don't know if Charlie CC'd you on this from the AeroElectric-List, so I've sent it on to the both you and the Lancair list. Regards, Mark Time: 08:37:54 AM PST US From: Charlie England Subject: Re: AeroElectric-List: RE: Avionics=Black Art --> AeroElectric-List message posted by: Charlie England Impossible to give an answer to the specific question without seeing the diagrams for the products, but the general answer is this: If the shield is nothing but a shield, it probably should be grounded at only one end. The most obvious example is the shield on a magneto P-lead. If the shield is actually the ground return for the circuit (common occurrence for audio & RF antennas) then it must be *connected* at both ends, which isn't necessarily the same as being *grounded* at both ends. The most obvious example for this is headset & mic wiring to the intercom or radio. In those cases, the shield is also the ground return for the mic & headphones, so must be connected to both the intercom & the jack, but it must *not* be *grounded* at the jack; that's why you are instructed to use insulating washers on the jacks. This is where the ground loop can show up, when there would be 2 paths for the return current to follow: the shield line & the airframe. (hope that didn't just stir up more mud in the water...) >>-----Original Message----- >>From: Greenbacks, Ltd. [mailto:N4ZQ@comcast.net] >>Sent: Friday, April 14, 2006 23:23 >>Subject: Re: Avionics=Black Art >> >> >>Before igniting a spirited discussion on the subject of wiring a >>panel, I'll cheerfully disclose that I have no formal training and >>have a hard time trying to explain how an electron moves from one >>place to another. This said, how do we resolve an apparent conflict. >>The technical wizards at Garmin say in no uncertain terms that with >>shielded cables (comm primarily) the shield must be grounded at both >>ends. Other technical wizards at L3/Goodrich Avionics(WX500 >>Stormscope) are adamant that shielded cables (Tx/Rx) must only be >>grounded at one end. In the case of the Wx500 talking the the MX20, >>the Tx cable is to the shielded at the processor end only and the Rx >>cable shielded at the MX20 end only. Never mind the fact that the >>WX500 install manual calls out for these cables to be shielded at >>both ends. >> >>I suspect there may be a ground loop potential in here somewhere and >>would welcome feedback from anyone one on the list who actually makes >>a living do'in this stuff day to day. >> >>I've got the WX500 up and running on the bench and haven't blown the >>thing up yet so maybe there's hope. ): >> >>Angier Ames >>N4ZQ >>N3ZQ