Spectrum demystified

The Central government received commitments totalling more than Rs 1,00,000 crore from telecom operators as the eighth day of bidding in e-auctions of radio frequency (RF) spectrum concluded on March 12. RF spectrum is a band of invisible electromagnetic airwaves used to transmit or receive signals. The mobile phone you make and receive calls from, the FM radio you listen to, the TV programmes you watch or the GPRS devices you use, all function by receiving and transmitting these invisible signals.

How is it measured? In hertz (Hz), named after German physicist Heinrich Rudolf Hertz, who first proved the existence of such electromagnetic waves in the 1860s. One hertz or one wave, like in a heartbeat, is of one-second duration.

Humans can typically hear sounds in the range of 20 Hz to 20,000 Hz or 20 Khz (kilo-hertz). Below this range it is infrasound and above that ultra sound, both of which are inaudible.

Since this electromagnetic spectrum is scarce and is used for multiple disciplines -- such as defence, railways, radio, TV and telecom – it is divided into bands for better management, easier assignment and to assign a cost.

When one refers to, say, a 900 MHz band, the range typically extends from 869 MHz to 915 MHz in India, but for easier identification, it is collectively called the 900 MHz band. So it is not a single frequency.

All put together, the government is offering in this e-auction a total of 103.75 MHz in the 800 MHz band over 85 blocks, 177.8 MHz in the 900 MHz band over 889 blocks, 99.2 MHz in 1,800 MHz band over 496 blocks and 5 MHz in the 2,100 MHz band over 17 blocks. The 20-year spectrum licence, which is given at each instance, is expiring in December 2015 for some operators.