Skip to main content

Exploring communications technology

Completion requirements
View all sections of the document

The frequency bands are arranged horizontally, on a scale that is marked at 0, 4.3125 kilohertz, 25.875 kilohertz, 138 kilohertz, 1.104 megahertz, and 2.208 megahertz.

On the left there is a small rectangular blue section labelled ‘POTS’. This ranges from 0 to 4 kilohertz. It is numbered 0.

There is a gap between 4 kilohertz and 25.875 kilohertz. This is marked as unused and subdivided into subchannels 1 to 5. The numbers are labelled ‘subchannel numbers (indexes)’. A horizontal arrow indicates that each subchannel width is 4.3125 kilohertz.

Then there is a rectangular green section labelled ‘upstream’. This ranges from 25.875 kilohertz to 138 kilohertz. It is divided into subchannels 6 to 31. One subchannel, for which no number is given, is labelled ‘pilot’.

Finally, on the right, there is a large rectangular red section labelled ‘downstream’. This ranges from 138 kilohertz to 2.208 megahertz. It is divided into subchannels 32 to 511 (but subchannel 32 is white as it is not used). One of the midrange subchannel, somewhere between 33 and 255, is labelled ‘pilot’.

Within the red area, the range of ADSL1 and ADSL2 is represented by a horizontal arrow from a frequency of 138 kilohertz to a frequency of 1.104 megahertz (subchannels 32 to 255). The range of ADSL2+ is represented by a horizontal arrow from a frequency of 138 kilohertz to a frequency of 2.208 megahertz (subchannels 32 to 511).