Conversion from 3 Gigahertz to Kilohertz

Information about the Gigahertz (GHz)

The gigahertz is a unit of frequency equal to one thousand million hertz. Its symbol is GHz. It is the range of modern wireless communication and of the clock inside every current computer, and almost nothing in it was in everyday use before the 1990s.

Wi-Fi occupies two main bands, at 2.4 and 5 gigahertz, with a newer band near 6. The 2.4 gigahertz band is crowded because it is licence-free almost everywhere and shared with Bluetooth, cordless phones and microwave ovens, which operate at 2.45 gigahertz because water molecules absorb energy efficiently there. The 5 gigahertz band offers more channels and higher rates but is absorbed more strongly by walls, so it covers a smaller area.

Mobile telephony spans the range. Earlier generations used bands below 1 gigahertz for their long reach into buildings and across countryside, while newer allocations at 1.8, 2.6 and 3.5 gigahertz carry more data over shorter distances. The higher a frequency, the more bandwidth is available and the less it penetrates, and every generation of network design is a negotiation between those two facts.

Computer clock speeds crossed into gigahertz around the year 2000 and stalled near four a few years later. The limit is thermal: power dissipation rises steeply with frequency, and beyond about four gigahertz a conventional silicon processor cannot shed the heat. Performance gains since then have come from adding cores, widening instruction issue and improving memory hierarchies rather than from raising the clock.

Satellite links, radar and radio astronomy all work here. Weather radar typically runs between 2.7 and 5.6 gigahertz, air traffic control radar in similar bands, and the microwave background radiation that fills the universe peaks near 160 gigahertz, well above the range of terrestrial communication.

Millimetre-wave systems at 24 gigahertz and above are used for automotive collision-avoidance radar and for the highest-capacity mobile network bands. Their very short wavelengths allow small antennas and enormous data rates but are blocked by almost anything, including rain and foliage.

One gigahertz equals one thousand million hertz, 1000 megahertz, or 0.001 terahertz.

Information about the Kilohertz (kHz)

The kilohertz is a unit of frequency equal to 1000 hertz. Its symbol is kHz. It covers the upper part of human hearing and the lowest part of the radio spectrum, which makes it the meeting point of two very different technologies.

Audio lives here. The upper limit of human hearing is about 20 kilohertz in a young person, and the frequencies that carry speech intelligibility cluster between 1 and 4 kilohertz. Digital audio is sampled at 44.1 kilohertz for compact discs and 48 kilohertz for video work, rates chosen because the sampling theorem requires more than twice the highest frequency to be reproduced, with a margin for filtering.

Radio broadcasting began in this range. Long wave runs from 148 to 283 kilohertz and medium wave, the AM band, from 526 to 1606 kilohertz. These low frequencies propagate along the ground and reflect off the ionosphere at night, giving them ranges of hundreds or thousands of kilometres from a single transmitter, which is why they carried the first national broadcasting services and still serve maritime and aviation navigation beacons.

Submarine communication uses even lower frequencies because seawater absorbs radio energy, and only signals in the range of a few kilohertz and below penetrate more than a few metres. Naval very low frequency transmitters occupy enormous antenna arrays for this reason, and their data rates are correspondingly tiny.

Ultrasound for medical imaging sits far above the audible range, in megahertz, but industrial ultrasonic cleaning and animal deterrents work between 20 and 80 kilohertz, just above what people can hear. Bats echolocate in the same territory, from roughly 20 to well over 100 kilohertz.

Older computers had clock speeds in kilohertz. The processor in the original Apple II ran at just over one megahertz, but the earliest microprocessors and many microcontrollers still operate at a few hundred kilohertz where low power matters more than speed.

Digital audio put a specific number from this range into everyday use. The compact disc samples at 44.1 kilohertz, chosen because the sampling theorem requires more than twice the highest frequency to be reproduced, and twice 20 kilohertz leaves a margin for the filter that removes everything above it. Professional recording commonly uses 48 kilohertz to match video, and 96 or 192 for mastering. Telephony sits far lower, sampling at 8 kilohertz and so cutting off above about 3.4, which is why a voice on an ordinary phone line loses the sibilance that makes the letters s and f easy to tell apart.

One kilohertz equals 1000 hertz, 0.001 megahertz, or one millionth of a gigahertz.