---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Mon 07/22/13: 3 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 12:51 PM - Re: Garmin 496 with Trutrak Autopilot, Dynon EFIS D100 and Garmin SL30 (Robert L. Nuckolls, III) 2. 05:12 PM - Killer headset deal at Spruce (jonlaury) 3. 05:22 PM - Re: Battery Cap Tester (jonlaury) ________________________________ Message 1 _____________________________________ Time: 12:51:41 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Garmin 496 with Trutrak Autopilot, Dynon EFIS D100 and Garmin SL30 At 09:31 PM 7/21/2013, you wrote: Bob and I differ on where to terminate the screen, but that drills into some serious minutiae on this project. It's probably just not necessary at all. (Bob -- I wouldn't mind hearing your thoughts on the termination location rationale though) Sure . . . easy . . . flip a coin. Shielding is a prophylactic against the weakest of all EMI propagation modes - electrostatic. Modern serial data signals will deliberately soften the leading and trailing edges of the data to minimize the strength of the propagation mode in bundles. Twisting pairs of a balanced data stream (Like RS422) drops the coupling mode to a small fraction of and already weak coupling mode. Twisting an unbalanced data stream can't exploit the common mode rejection capability of a balanced pair receiver . . . but it still reduces electrostatic coupling by a substantial proportion. Shielding breaks the electrostatic propagation mode. The currents flowing in the shield are so tiny as to be difficult to measure . . . one can terminate the shield at ANY low impedance node tied to signal or power ground and it's got all the conductivity needed to do its nearly insignificant job. Grounding shields at the listener-end is a convention we used most places I worked . . . a convention not driven by significant physics. P.S. In some cases, the system designer will specify that the outer conductor of a shielded wire be connected at both ends. This is a perfectly valid means by which a 'ground' can be carried along with the shielded signal wires but the system designer will also have addressed any risks for creating a ground-loop on the double terminated shield. In all other cases, single end grounding is the legacy convention although in cases where the shielded wire runs a couple of feet between panel mounted black boxes, risk of shield induced ground loop is non-existent. Bottom line suggests that studying the installation wiring diagrams for shield handling is a good practice. The legacy conventions evolved out of large aircraft systems wherein small signal wires run considerable distances through hostile electrical environments with HIGH risk off shield induced ground-loops. Except for legacy magneto p-leads, I suspect all other shields could be left un-terminated or even deleted from the wire bundle with no adverse effects. Bob . . . ________________________________ Message 2 _____________________________________ Time: 05:12:36 PM PST US Subject: AeroElectric-List: Killer headset deal at Spruce From: "jonlaury" If you're at the point of needing a headset, ACS is selling Beyerdynamic HS 800 headsets for $625. These are German engineered and manufactured noise cancelling sets. Search my name for my comparison with Bose sets at a Bose distributor with a single engine cabin noise simulator. The post date was Oct 04, 2011. Do Not Archive Read this topic online here: http://forums.matronics.com/viewtopic.php?p=405117#405117 ________________________________ Message 3 _____________________________________ Time: 05:22:41 PM PST US Subject: AeroElectric-List: Re: Battery Cap Tester From: "jonlaury" nuckolls.bob(at)aeroelect wrote: > > Bob > > I'll try it again to see if I get something different. > > > Bob . . . After a night on the charger and a few hours rest, started at 13.0 volts and after 2 hours of 75 watt draw, disconnected lamp and measured 12.0 The relatively high day to day discharge turns out to be attributable to having left my pilot side NC headset (battery bus) on. The LED indicator was facing the seat back. 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