[Boatanchors] 2nd Newbie Q

[hwhall at compuserve.com]

Someone will correct me if I'm wrong but if I recall correctly one ought to have the equipment being connected sharing a single good ground, so that there won't be ground current loops when one connects shielded cables. I realize, though, that achieving such a ground can be non-trivial or  impractical at times. 

As others noted, you can't get away with the shield connected at only one end if the shield is also part of the signal carrying circuit through the cable (very commonly the case). In that case, one may be forced to improve the grounding so that the cable shield connection doesn't cause trouble.


 Wayne

 WB4OGM

 

-----Original Message-----
From: W2HX <w2hx at w2hx.com>
To: Bob Jackson <bob145 at suddenlink.net>; qth.boat <boatanchors at mailman.qth.net>
Sent: Wed, Sep 10, 2014 2:30 pm
Subject: Re: [Boatanchors] 2nd Newbie Q


The reason is, if you attach shield on both ends, you have a risk that the 
ground potential of the two ends are not the same exactly the same (Think of 
interconnecting two different devices together with coax. Like an exciter and 
amplifier plugged into different house circuits). If they are not exactly the 
same, a current will flow. If the current has any AC component on it, it will 
induce an AC signal on the inner conductor(s) of the cable which is exactly what 
you are trying to avoid by using a shield in the first place.  

With only one end attached, you get the shielding properties and no risk of a 
current on the shield. Hope this helps

73 Eugene W2HX

-----Original Message-----
From: Boatanchors [mailto:boatanchors-bounces at mailman.qth.net] On Behalf Of Bob 
Jackson
Sent: Wednesday, September 10, 2014 11:30 AM
To: porch.boat; puck.boat; qth.boat
Subject: [Boatanchors] 2nd Newbie Q

I've noticed that some construction articles involving the use of shielded 
cables advise that the shield be connected at only one end but they don't say 
which end, i.e. near or far. Also, when is this practice most useful and why?

Thanks again,

Bob  AG5X
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