[ntp:questions] GPS 18 LVC (Ground Wire Question)

unruh unruh at wormhole.physics.ubc.ca
Wed Mar 17 15:53:30 UTC 2010

On 2010-03-17, Alby <google at empire.org> wrote:
> On 16 Mar, 15:03, unruh <un... at wormhole.physics.ubc.ca> wrote:
>> On 2010-03-16, E-Mail Sent to this address will be added to the BlackLists <N... at BlackList.Anitech-Systems.invalid> wrote:
>> > Alby wrote:
>> >> (Garmin GPS 18 LVC, 5m).
>> >> So can I assume the extra thin black wire is just an
>> >> ?additional ground wire?
>> > One black wire is the power common,
>> > ?another black wire is the data common,
>> > ?the third black wire is a shield drain.
>> What is a "shield drain" and how do you know this? It is just off the
>> top of your head, or is there some more authoritative source for this
>> info?
>> (anyway, it sounds like there is nothing to prevent you from tying all
>> grounds together, unless the power comes from a source with a separate
>> ground from what the data ground is tied to, which could give bad ground
>> loops. In that case I would assume that you would tie the shield ground
>> to the power ground.
>  I think I figure it out.  The extra black wire on my GPS Unit is
> because my
> model is a Garmin GPS LVC, 5m. The typical unit is a 3m. Meaning my

So are mine (2 of them) GPS18LVC 5m units. And they onlyhave 2 black wires.

> cable length
> is 5 meters long, while the standard is 3 meters. Given the extra
> distance in my
> cabling, the additional black wire is performing the function of an
> electromagnetic shield.
> The poster who mentioned "drain wire" jogged a memory.
>  drain wire definition - telecom
> A wire wrapped around or part of a shield within a cable that reduces
> the resistance from any point on the shield to ground. A drain wire
> serves to complete an electrical circuit from the shield, thereby
> carrying extraneous electrical noise to ground and away from the
> circuit or system the shield is intended to protect. See also ground,
> ground wire, and shield.
> http://www.serialphy.com/multi-conductor-cable.bmp

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