How far can a Serial and/or USB cable operate?

Posted on 2011-05-11
Last Modified: 2012-06-21
I am being asked to network two devices.

One device has a serial adapter.

One device has a standard USB adapter.

The cable length is approximately 250 - 300 feet.

What is the operational length of a USB cable?

What is the operational length of a Serial cable?

What are suggestions regarding media conversion or other solutions?

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Question by:c-h-r-i-s-t-o-p-h
    LVL 82

    Accepted Solution

    USB is limited to about 5 meters (16 feet) and the length of RS232 serial cables is dependent on the data rate but it's still only 10 meters at 56Kbps.  If it is affordable, a fiber interface is the best technical choice because it can be used over very long distances and it provides electrical isolation that prevents ground loop currents.  Here are examples from one company:
    LVL 32

    Expert Comment

    What do you mean by "network"?  Are you just trying to connect to them with a long extension cable? (Nothing to do with networking.)

    If so, then you need an extension device.  I have an USB extender that uses Cat5 to carry the signal up to 200 feet.  It's only USB 1.1, not higher-speed 2.0, and definitely not 2.0.

    Here's a newer version that has 4 ports and up to 12Mbps speed:

    If your devices are next to each other, then plug in the USB device, and get a USB-serial adapter for the other device.  Then plug both into the hub extender.
    LVL 32

    Assisted Solution

    This one uses fiber for up to 2,000 meters, and can also carry DVI video:

    This model is an active USB cable that can be daisy chained.  50 meters per cable, so you'd need a few.  But, troubleshooting would be difficult if there were a problem:
    LVL 70

    Assisted Solution

    Even with extenders, 250-300 feet is definitely "pushing the edge" on what you may be able to achieve with USB/Serial technology.

    A few alternatives:

    I.   Use a serial Bluetooth adapter on the serial port side [ ]  and a USB bluetooth adapter on the other end.

    II.  Just add a USB NIC on the USB side [ ]
    ... and a serial NIC on the serial port side [ ]

    III.  Add a simple network adapter on one or both ends instead of the adapters in (II).     This is the simplest (and least expensive) alternative.

    Just do any of the above; then get an ethernet cable of the appropriate length (except for option I, which is wireless).     Note that Cat-5 can officially run up to 100 meters (328 ft), although I've used 400 ft cables with no problem.
    LVL 7

    Assisted Solution

    Since the one device is simply an RS232 unit, I would use a USB-to-RS-232 adapter on the unit with only USB. You'll likely need to load a driver.  Here's one unit at Radio Shack,, and another at Monoprice, although the one at monoprice doesn't mention a driver.  Then use a RS-232 extender which simply uses standard twisted pair wire to drive the RS-232 signal up to 1000 feet. Here's one at Monoprice

    For "networking" the two devices, you'll have to provide more information.  You don't include make, model, software, etc.  If they are both running a microsoft OS, you could probably use a copy of PC Anywhere (very old version if needed) which would let you transfer files.  If the OS is a bit more modern, you could do something a bit more traditional and simple.  If these are "devices" like connecting to a lab instrument, then you'll have to see what software is on each side.

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