The megahertz is a unit of frequency equal to one million hertz. Its symbol is MHz. It covers the part of the radio spectrum that carries most broadcasting and short-range communication, and it was the unit in which computer speed was measured for two decades.
FM radio occupies 87.5 to 108 megahertz almost everywhere, a band chosen after the Second World War because it was high enough to allow the wide channels frequency modulation needs and low enough for transmitters and receivers to be built cheaply. Terrestrial television took the neighbouring bands, and the switch from analogue to digital broadcasting freed large parts of them for mobile telephony.
Aviation communication sits just above FM radio, from 118 to 137 megahertz, using amplitude modulation rather than the clearer frequency modulation. The choice is deliberate: when two aircraft transmit at once, amplitude modulation produces an audible heterodyne squeal that alerts everyone to the collision, whereas frequency modulation would simply capture the stronger signal and silently lose the weaker one.
Computer processors were rated in megahertz from the late 1970s until around 2000. The original IBM PC ran at 4.77 megahertz, and the megahertz race that followed ended when clock speeds stalled near four gigahertz because of heat, after which manufacturers competed on core count instead. Memory bus speeds and display timings are still commonly quoted in megahertz.
Medical ultrasound works between about 2 and 18 megahertz. Higher frequencies give finer resolution but penetrate less deeply, so an abdominal scan uses a lower frequency than an examination of a superficial structure, and the operator chooses the probe accordingly.
Radio-frequency identification, garage door remotes, wireless microphones, marine VHF and amateur radio all live in this range. So do the harmonics that make poorly shielded electronics interfere with each other, which is why regulatory testing concentrates on emissions in the tens and hundreds of megahertz.
Mobile telephony has made the unit a matter of money. Spectrum is auctioned in blocks measured in megahertz, and governments have raised sums in the tens of billions from bands at 700, 800, 900, 1800 and 2600 megahertz. Physics sets the value of each: lower frequencies travel further and penetrate buildings better, so the 700 and 800 bands cover rural areas cheaply, while the higher ones carry more data over shorter distances and suit cities. An operator's coverage map and its data speeds are therefore both consequences of which megahertz it managed to buy, which is why the auctions are followed as closely as any other national asset sale.
One megahertz equals one million hertz, 1000 kilohertz, or 0.001 gigahertz.
| Unit | Symbol | 1 Megahertz equals | 1 of these equals | Converter |
|---|---|---|---|---|
| Nanohertz | nHz | 1 × 1015 nHz | 1 × 10-15 MHz | Megahertz to Nanohertz |
| Microhertz | µHz | 1000000000000 µHz | 1 × 10-12 MHz | Megahertz to Microhertz |
| Millihertz | mHz | 1000000000 mHz | 0.000000001 MHz | Megahertz to Millihertz |
| Hertz | Hz | 1000000 Hz | 0.000001 MHz | Megahertz to Hertz |
| Kilohertz | kHz | 1000 kHz | 0.001 MHz | Megahertz to Kilohertz |
| Gigahertz | GHz | 0.001 GHz | 1000 MHz | Megahertz to Gigahertz |
| Terahertz | THz | 0.000001 THz | 1000000 MHz | Megahertz to Terahertz |