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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 <ceengland@bellsouth.net>
Subject: Re: AeroElectric-List: RE: Avionics=Black Art
--> AeroElectric-List message posted by: Charlie England
<ceengland@bellsouth.net>
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
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