atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services Cabling Telephones Systems Wiring RS232 distance

Hey Guys-
On our Mackie DX8 sound systems, we have a program that runs on a computer so we can control all of the settings/levels. It uses a female DB9 connector and is RS232. I am wondering what the distance limitations are for this connection. I need some longer cables and I am not sure how long it can be without causing a problem.

With high quality cable you can go as far as 50 feet without issues. Beyond that you will have problems at higher baud rates. Now in the old days we used short haul modems also known as line drivers. With them we could get some amazing performance often in excess of 1000 feet. You could use CAT5 with a line driver on each side. But if you go unconditioned, plan on 50 feet or less.

The spacs for rs-232 say 50', but people have successfully used cable runs of a couple hundred feet. A lot of it depends on the speed, and the cable used.

If you need longer distances, try finding some line drivers that convert to/from rs422 or rs485, BlackBox is a well known source. Specs typically claim 115.2 up to 4kft.

BTW: it's a DE-9 (the second letter indicates the physical connector shell size.)

It's definitely not that long of a run, less than 50 feet. I just want to be able to use my laptop outside the room where the rack is.

I have never had any instances where we'd use anything more than our 10'null modem cable, but I am interested in these line drivers... any links and or suggestions? (I see tantivy suggests BlackBox) I know nothing about this line driver at this point

Thanks!

Tony -

I'm looking at a pair of Blackbox shorthaul modems part # VDE-0871-B.

We used to use them to extend serial printers and dumb terminals off the ACD. We'd have runs of a 1,000' without a problem.

Sam

I couldn't find that in the Black Box website. A google search said it is a line driver.

Line drivers are also known as short haul modems, and are basically modems designed for operation across dedicated pairs. Some use RS422 (balanced 4w), or RS485 (balanced 2w) for inter-modem communication, some use some other method.

Usable distance and speeds vary, generally you trade speed for distance. They are available as port powered, or externally powered versions.

With RS485, you can run them in a multipoint configuration, either to a multiplexer, or a terminal controller. They are commonly used for industrial controls, linking PLCs or other devices, but you used to see them in lots of other situations, such as travel agents, or library terminals, where there were a lot of terminals multiplexed into a single leased-line modem.

Stanford used to have this box called a Gandalf switch, which fed 4w circuits across the campus, allowing connections to a number of devices, including the campus mainframes, and a central terminal server pool. Before the proliferation of PC's, there used to be terminals in every office, all connected to the Gandalf switch. Some departments (EE. CS. etc) had LAN's with local terminal servers. but some places only had a single terminal for a department administrator.

There were two versions of these line drivers, one was externally powered, and had a thumbwheel switch, which allowed the user to select a specific system to connect to. The other was a port powered unit about the size of a pack of cigarettes, and the user selected the system via a menu once the port was activated. The port powered drivers appear to be RS422 based, and they work just fine when wired back to back. I have used them at 9600bps over a 10kft loop.

Speaking of modems, if you have a pair of modems that can be set to operate without dialtone, you may be able to use them over a limited distance over a dry pair. The configuration can be a bit tricky, since you don't have ring voltage, but it does work. You basically have to set one end to answer mode, go offhook, and no timeout.

I have used a USR Sportster to communicate with an Apple Airport over 150' of dry pair. The Airport was running PicoBSD unix, using the modem port as the console.

duplicate post.

look for Black Box part numbers:
ME800A-PLUS-R2
ME800A-R3
ME755A
ME890A
ME6100A
ME6101A
ME6102A
ME795A
ME796A
ME1791A
ME1794A
ME1721A
ME1821A
ME1862A
ME1863A
ME790A
ME792A
ME794A
ME775A
ME776A
ME777A
ME3000A
ME3001A
ME3002A
ME3003A

These are all point-point async rs232<->copper short haul modems. there are also multidrop, wireless, and fiber versions..