I understand that one still needs to run a ground (though it is thought
of as shield, since it is connected to the shield of the xlr 5 pin
connectors) But the ground should never be directly connected the
receivers, only the master console (transmitter).  I know some couple it
to the receiver's ground through a small cap, and some even tie it to
ground through a resistor.  However, I don't think this problem (ground
potential differences over long runs) has been solved to anyone's
satisfaction.

-Adam

Harold M Hallikainen wrote:
>
> On Wed, 15 Sep 1999 11:42:15 -0400 "M. Adam Davis" <adavis@UBASICS.COM>
> writes:
> >DMX-512 does not need to be run over shielded cable.  About all the
> >spec
> >says is that it follows the rs-485 spec, which in turn states that
> >cables only need to be shielded if any of the following if very high:
> >Distance, noise, and data rate.  The DMX-512 is not considered a high
> >data rate, so you only need shielding if you are running cables a long
> >way (> 100m), or if there's a lot of electrical noise in the area.
> >
>
>         When you don't run a shield, what do you do to establish a
> "common" for the receiver?  It's fairly common (in fact, required in the
> upcoming revision of the DMX512 spec) to float the receiver to avoid
> ground loops.  It seems that we need to either run a wire (such as the
> shield) back to the common at the transmitter, or, perhaps, have clamp
> diodes on the inputs of the receiver to force the receiver common to the
> appropriate voltage.
>         Thoughts?
>
> Harold
>
> Harold Hallikainen
> harold@hallikainen.com
> Hallikainen & Friends, Inc.
> See the FCC Rules at http://hallikainen.com/FccRules and comments filed
> in LPFM proceeding at http://hallikainen.com/lpfm
>
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