Cable Lengths

Posted on 2001-06-07
Medium Priority
Last Modified: 2010-04-29
I have a printer that is connected to the back of my Data General mini computer that uses serial db25 as a connections.  I use a db25 to rj45 converter so I can use the exsisting network cabling instead of running serial cables everywhere.  I need to know what the distance limitation of a serial cable is.  Or in this situation is the distance converted to the capabilities of the cat 5 cable?
Question by:mtbuford
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LVL 23

Expert Comment

ID: 6164831
I have heard the maximum is 300ft.  I had also heard a max of about 60ft on a parallel cable.  I have run parallel successfully using two 6ft cables at each end and a 100ft straight through cable.
LVL 31

Expert Comment

ID: 6164843
Interesting question. The maximum cable length would depend on transmission speed, cable properties and signal level. Cat5 cable should be good for pretty long distances at serial communication (RS232) speeds, at least the same length as allowed for LAN use. Problem might be signal level, but that's difficult to say much about. COM port output level is pretty high, like +- 12 V, but cable losses occur of course, and they depend somewhat on what is in the other end. I hooked two computers up in a serial link (running interlnk/intersvr at 115 kbps) that was 60 ft and it worked OK. This was a cheapo multiple TP telephone cable. I'll listen to othe comments with interest.
LVL 32

Expert Comment

ID: 6164886
Assuing that this interface is an RS-232 standard interface (which seems likely) you have a length/performance derating to be aware of.  In general, the specification calls for up to 75 ft. at 9600 bps.  Longer runs can be made but the speed will need to be reduced.  Shorter cables can run faster.

Remember, however, that this is WORST CASE.  In general your cable is better than the minimum required by the spec, your drivers have better output signals, your receivers are better, and your noise environment is not as bad as the spec permits.  You can also extend the distance by using better (i.e. more shielding and larger wire gauge that called for).

In general, however, CAT5 UTP cable is NOT THE BEST choice for RS-232 signals.  The difference is that RS-232 is SINGLE ENDED and 10BaseT network signals are DIFFERENTIAL.  The UTP cable is just that, UNSHIELDED TWISTED PAIR, which is excellent for DIFFERENTIAL signals but poor for RS-232 single-ended.

The best choice for RS-232 is SHIELDED multi-conductor 16 to 18 ga. stranded copper wire.
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LVL 12

Expert Comment

ID: 6165011
You can also use a device called a Short Haul Modem to extend your RS-232 distances as far as a mile over standard UTP cable.

Expert Comment

ID: 6165175
You can reach 300m with RS232 ( it uses +12V/-12V) for log 0/1) and more than 1000m with simple converter RS232/current loop. (it uses 20mA current).

Expert Comment

ID: 6198410
mtbuford, you have over 20 questions open right now, some from last October. Many experts have spent a significant amount of time trying to help you and you have failed to respond. Please do them the courtesy of returning to these questions and finalizing them. You can find a list of these questions by looking into your profile (click on your name in the upper left corner of this page) and looking into the question history.

experts, I apologize for barging into your question like this. I hope that mtbuford will not treat this question (and its experts) as he/she has so many others.

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Expert Comment

ID: 6228542

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Hi Experts:

In the event that the Asker does not respond, I would very much appreciate your opinions as to which Expert ought to receive points (if any) as a result of this question.  Likewise, you can also suggest that I PAQ or delete the question.

Experts, please do not add further "answer" information to this question.  I will be back in about one week to finalize this question, earlier if comments received.

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Expert Comment

ID: 6283795
Hi all,

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Accepted Solution

ComTech earned 0 total points
ID: 6313305
No one has returned to this question after the notification.

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I shall accept my own comment as to preserve the information at 0 points.

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