[BC] Long serial connections

[Harold Hallikainen]

> Hello,
> Quick question...
>
> What is the longest serial/com port run that will still work?
> We just moved studios, and want to have our Sage Endec in studio, while
> still having our Multi Station Relay back in the rack room.  (Pretty good
> piece of ground to cover.)
> I'm having trouble getting it to work at all now, and I'm wondering if the
> distance could be to blame?
>
> Any one have experience with long runs like this?
>
> Thanks in advance,
> Evan Elrod

http://en.wikipedia.org/wiki/Rs232 says EIA232 is typically good for 50
feet with standard cables and up to 1,000 feet with low capacity cable.
There are a couple issues. First is cable capacity limiting the slew rate
of the signal. Lower data rates should be able to go farther since there
is more time for a bit to settle. The second issue is ground loops. Since
EIA232 is unbalanced or single ended, any ground potential difference is
added to the data, possibly giving bad data levels. There are "RS232
Extenders" that typically convert EIA232 to EIA422 and run it over CAT5
cable with a separate pair handling the data in each direction. EIA422
uses differential signaling, so ground loop issues are minimized. It also
uses impedance matched lines so reflections and line capacity issues are
reduced.

Harold

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