Network - Bandwidth
Bandwidth refers to the amount of data a cable can carry; measured in bits per second (bps) for digital signals, or in hertz (Hz) for analog signals such as sound waves. An analog bandwidth is computed by subtracting the lower frequency from the higher one. For example, the bandwidth of the human voice is roughly 2,700 Hz (3,000 - 300). A larger bandwidth means greater potential data-transmission capability. For digital signals, a higher bit rate represents a larger bandwidth. However, the higher the frequency, the shorter the wavelength. A higher bandwidth (that is, a higher signal frequency) means faster transmission, which means a shorter signal. With a short signal, there is a smaller margin for error in interpreting the signal. This means that the effects of attenuation and other signal distortion must be kept to a minimum. A signal traveling along a cable degrades with distance. It is possible to connect the cable to special components that can clean up and rejuvenate a signal. High-frequency electrical signals must be cleaned up WHAT TO LOOK FOR IN A BALUN Baluns may include a stretch of cable (at extra cost, of course). Here are some things to consider when you're shoppping for a balun: n Baluns work most reliably when the cable has low capacitance (20 picofarads/foot or less) and when the cable impedance is not too high. n Baluns are available in different qualities, based on the type and gauge (thickness) of cable at either end. Make sure the balun you select supports the cable properties and distances you need and then some. To be on the safe side, don't use a balun (or any other kind of connector, for that matter) at the maximum rated length. n Some network interface card manufacturers recommend specific baluns for their boards. Similarly, some manufacturers suggest that you do not use baluns with their hubs or cards. Check with the manufacturer to determine whether either is the case with the network interface card or hub you plan to use. n When using a balun on a network, you'll almost certainly want a balun designed for data transmission, because this type is made for direct (rather than reversed) pin-to-pin connections. n Baluns pass signals on, so the balun's reliability depends on the signal's quality. For this reason, it's not a good idea to use a balun with passive hubs, which don't clean and strengthen the signal before passing it on. frequently, which means single cable segments must be short. Some commonly used frequency bands for analog transmissions are shown in the table "Bandwidths on the Electromagnetic Spectrum." Very low frequency (VLF) through super high frequency (SHF) are considered the radio spectrum. The bandwidths are used as follows: n AM radio broadcasts in the medium frequency (MF) range (535 to 1,605 kHz). n FM radio and VHF television broadcast in the very high frequency (VHF) range (88 to 108 MHz for FM; the split ranges from 54 to 88 MHz and from 174 to 216 MHz for VHF television). n Cable stations broadcast over several bands (frequency ranges) in the VHF and ultra high frequency (UHF) ranges (108 to 174 MHz in the VHF range; 216 to 470 MHz in the VHF and UHF ranges). n UHF television broadcasts in the UHF range (470 to 890 MHz). n Radar operates at 10 different bands over a huge frequency range (230 MHz to 3 THz). Radio Spectrum Bandwidths For digital transmissions, bandwidths range considerably. Here are some examples of bandwidth values for digital transmissions: n Some digital telephone lines: less than 100 kbps n ARCnet networks: 2.5 Mbps n ARCnet Plus networks: 20 Mbps n Ethernet networks: 10 Mbps n Fast Ethernet networks: 100 Mbps n Token Ring networks: 1, 4, or 16 Mbps n Fast Token Ring networks: 100 Mbps n Fiber-optic (FDDI) networks: About 100 Mbps, but can theoretically be several orders of magnitude higher n ATM networks: about 655 Mbps, with speeds as high as 2.488 gigabits per second (Gbps) in the future