The Difference Engine: Bigger Than Wi-Fi

From The Economist:

HAVE you ever wondered, if you are of an age with your correspondent, about those missing channels on old television sets? Apart from channel two, the rest of the original VHF channels on the dial were usually just the odd numbers from three to 13. That was because, in over-the-air VHF broadcasting, the channel between two analogue stations had to be left unused so that it would not interfere with adjacent ones. When UHF broadcasting came along, empty “guard bands” were added to each channel for the same reason. In some places, this so-called “white space” of unused frequencies separating working channels amounted to as much as 70% of the total bandwidth available for television broadcasting.

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