| Author | Message | ||
     Anonymous |
what is bandwidth? | ||
| Simon Quellen Field (Sfield) |
Bandwidth is the amount of information you can send over a communications channel in a given amount of time. A "band" is a range of frequencies allocated to a particular use, such as communicating between two radios. When you modulate a carrier wave, you get the sum and difference frequencies between the carrier and the modulating signal. So, if you have a 1 Mhz carrier frequency, and you whistle a low "A" note at 440 hertz to modulate it, you will get four frequencies out: 1,000,000 hz, 440 hz, 1,000,440 hz, and 999,560 hz. The 440 hz signal is filtered out by the radio, and the other three are used to reproduce the sound at the receiver. The "width" of the band needed to transmit your whistle is 880 hz, the range between 999,560 and 1,000,440. But if you want to reproduce high fidelity music, you might want to send all of the frequencies that your ear can hear. That ranges from perhaps 20 hz to as high as 20,000 hz. So, to send all of those high notes, you need to use the frequencies ranging from 980,000 hz to 1,020,000 hz. This is a bandwidth of 40,000 hz. Sending high speed computer data requires even higher bandwidths. Cable modems and DSL lines need as much as 5 million bits per second, or a bandwidth of 10 million hertz. This is referred to as "broadband" communications, because of the wide bandwidth. 802.11g radios use even more, going up to 54 million bits per second. |
