Shyam Ponappa / New Delhi March 4, 2010
[Added later - May 26, 2013:
For more details on what spectrum is, please see the footnote.1 The rest of the article is on the uses of spectrum.]
- Radio waves are relatively long, with wavelengths from 1,000 metres (1 km) to 10 cms, and frequencies from 3 kilohertz (3,000 cycles per second) to 3 gigahertz (GHz) or 3 billion cycles per second for the shortest, sometimes also called microwaves. (There are longer waves, e.g., electric power, of several km.)
- Microwaves in the centimetre and millimetre range can have frequencies up to 300 GHz. There is an overlap in terminology depending on use; microwaves for cooking use several hundred watts of electricity at RF wavelengths of about 32 cms (915 MHz) and 12 cms (2.45 GHz). Microwaves from low-powered devices of a few watts at these frequencies are used for communications, and emit insignificant heat.
- Infrared waves are smaller, and are felt as heat, e.g., from lamps and infrared grills used for cooking. Higher infrared bands used for communications in remote control devices and for imaging/night vision have no heating effect.
- Wavelengths between 700 and 400 nanometres (about 430 to 750 terahertz or THz) form the visible spectrum from red to violet, combining to form white light. For example, we perceive wavelengths of about 635-700 nm (430-480 THz) as the colour red.
- Shorter wavelengths form ultraviolet rays, of which those around 380-280 nm cause sunburn. Sunlight at sea level comprises about 53 per cent infrared, 44 per cent visible light, and 3 per cent ultraviolet rays.
- Yet smaller waves are classified as X-rays, and the smallest as gamma rays, both used in medical and industrial imaging.
- Technology-neutrality: the UK and Norway have not restricted the use of recently auctioned spectrum to any technology.
- A focused strategy for service delivery at low cost, as in China.
shyamponappa at gmail dot com
Footnote - Added later: May 26, 2013
1 What is Spectrum?
May 26, 2013