null modem cable maximum length


Does anyone know the maximum length for null modem cables? Can I order one on the Internet to be shipped in the UK - any suggestions?

Many thanks,

Who is Participating?
AlexNekConnect With a Mentor Commented:
here you'l find for 10 meters
Max distance depends upoin speed ,about 50FT @19.2K.

As for cables
Doing the Google thing shows 15M (~50 feet) and 19.2K baud as the design limit for the original EIA RS-232 of 1962, which used -25V and +25V.  RS-232C of 1969 was a big step forward, tightening the signals to +/-15V and specifying the common D25 connector we all know and love, but I don't think that it changed the original design limits.  Rev-D changed it to a total line impedance limit, which makes a lot more sense.
   You can extrapolate as pqm554 said above: if you double the distance to 30 meters, is should still work if you halve the speed to 9.6K baud.  Keep in mind some other factors too:  Modern (packaged in an IC) UARTs produce a lot cleaner signal than the original discrete components did when the RS-232 standard was set, so you should be able to go a lot further and faster than the engineers expected back in 1962.  On the other hand, if you have a bad cable, or there's a lot of RF interference, then line noise will cut your speed down a lot. Routing your unshielded cable on top of a flourescent light will cause you a lot of trouble.
Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.

All Courses

From novice to tech pro — start learning today.