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Old 11-09-2011, 10:25 PM
JWT Kottekoe JWT Kottekoe is offline
Join Date: Apr 2003
Location: California
Posts: 966
I'm really not understanding your question. It should be clear that, if you want lots of bandwidth, you need to go to high frequencies.

Let's take some examples, AM radio stations in the US operate between 520 kHz and 1610 kHz, with a channel spacing (bandwidth) of 10 kHz. You can put 109 different channels in that band. 10 kHz is fine for talk radio and news but not great for high fidelity music. The FM band operates at more than 100 times the frequency, between 88 MHz and 108 MHz, with 100 channels and a spacing of 0.2 MHz (200 kHz) between channels. With 20 times the bandwidth, there is room for high quality stereo audio (plus guard bands to minimize interference, pilot tones, and other things). If you tried to do this in the AM band, there would only be room for five channels. Standard analog TV requires about 5 MHz per channel, so when the need arose for more than the original 13 channels, they had to go up another factor of ten in frequency, with UHF stations up to ~800 MHz.

These days, the ultimate in communications bandwidth is obtained at infrared and optical frequencies, where the frequency is measured in hundreds of terahertz and available bandwidths allow communication at terabit per second rates.