What is a megahertz?

"Wave frequency". Licensed under CC BY-SA 3.0 via Wikimedia Commons

You hear that term a lot, whether it’s a computer, radio, TV, or satellite installation. It seems like it’s a good way of measuring things, but did you ever stop to think about the term and what it means?

The hertz is a unit of measurement named after pioneer electricity theorist Heinrich Hertz, and it describes a complete cycle per second. If you can walk around in a circle fast enough that you make it around once every second, you’re walking at one hertz. If you can jump up and down once a second, you’re jumping at one hertz.

If you apply the normal metric system prefixes to “hertz” you get measurements that are usually used for something having to do with electricity. By their very nature, electromagnetic fields pulse in and out (or back and forth depending on your point of view.) They tend to do this fairly quickly. Regular electricity coming through your wall outlet pulses at 60 hertz, but radio transmissions start at 540 kilohertz (540,000 times per second) and go up from there. Most TV reception is in the 250-750 megahertz (250,000,000 pulses per second) while satellte transmission is in the gigahertz range. The greater the frequency, the longer a signal can travel but it requires more power to make it do so.

It’s worth mentioning that megahertz and gigahertz are also used to measure the speed of computer processors, and in this case the term refers to a complete instruction performed by a processing unit. Even though most things in computers are expressed in powers of two (for example a megabyte isn’t 1,000,000 bytes, it’s 1,024,578 bytes) megahertz aren’t like that, and can be any number needed.

It’s a useful term and it leads you to an understanding of the “electromagnetic spectrum” — the words that describe how radio waves of all frequencies can exist all around us and don’t interfere with each other in general. Some radio waves are visible to us, and we call those waves “light.” Some do such a poor job of passing through organic matter that they actually heat it up, and we call those waves “microwaves.” We use special devices to mess with the waves in such a way that they carry information that can be decoded later, and we call those “radio, TV and satellite.” At the end of the day it’s all electromagnetic radiation and the big difference between the types of waves… is measured in megahertz.