The cable length is determined by its electrical characteristics, such as RS232 cable length is limited to the maximum capacity of the data cable that does not exceed 2500pF. RS485 cable length is inversely proportional to its data transfer rate, which is also determined by the electrical characteristics such as capacitance and reflection.
Different USB cable length
USB1.1 stipulates that the cable length is 3 meters and USB2.0 stipulates is 5 meters. One of the reasons constraining the length of the cable is a cable delay. We know that the current almost travels by light on the cable, but it takes some time from this end to the other end. USB 1.1 defines the maximum delay time is 18 nsec, the USB2.0 stipulates 26nsec. The current speed passing through the copper wire depends on the dielectric constant of the surrounding material. Although we cannot precisely understand the argument, we can regard 65% of the speed of light as the speed of the current flowing through the ordinary cable produced by reliable usb cable manufacturer. Count down, the USB 1.1 maximum cable length is 3.51 meter, while the USB2.0 cable length is 5.07 meter.
The quality of the USB cable is more important than the length
In fact, the quality of the USB cable is more important than the length. You might find the cheaper cable has better value for money, but actually it is not the case. Although these cheap cables may work on some devices, but they can not necessarily work properly on all devices. This is because the USB specification allows the use of a variety of driver chips, the receiver chip and cable, if your computer has cheap driver chips (low speed and low power output), and just may encounter a crappy USB peripheral interface design, then the less expensive the cable may work, cheap cable may have a communication failure. This often causes driver bugs or the Windows problems.
Methods to overcome the limitations of USB cable length
Use HUB. The HUB is simply the splitter for repeaters and the USB signal and independently provides power supply. We are optimistic that the USB cable length limit is only limited to a length of cable, not the total length of the cable between the computer and peripherals. If you are using a HUB from professional custom cable manufacturer, the maximum length between the computer and peripherals will reach 10 meters that is the host is HUB5 meters, and HUB to the peripheral is 5 meters. USB standard stipulates, HUB allows cascading 5. If you are using a 5 m cable, the maximum distance between the host and peripherals is 30 meters, without the need for any irregularities. In such case, the Ethernet and wireless data connection will be simpler than this (5 HUBs, 6 cables).
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This article is come from:http://www.chinaphoneparts.com/index.php/usb-cable-length-limitations-and-breakthroughs.htm
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