|
|
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
|
|