If we had the ability to actually "see" airwaves, they'd probably block our view entirely. From radio station transmissions to handheld 2-way radio signals there must be thousands of signals in the air at any given time.

Shortwave radios (also known as receivers) allow for the reception of possibly hundreds of radio station transmissions from all over the world. How is it that a small radio can receive radio waves from countries transmitting from hundreds of thousands of miles away? Radio waves that are transmitted in other countries hit the earth's ionosphere, and then reflected back to other parts of the earth. Shortwave radios are built to receive these waves and possibly many others.

Most receivers can get signals from up to 13 different shortwave bands. In addition to the shortwave band, many radios can also receive AM/FM bands, along with LW and MW. Most shortwave radios are portable with a speaker built-in and some even come with built-in cassette players / recorders. The basic features of any shortwave radio include programmable stations, a headphone jack and a built-in antenna.

Shortwave radios can pick up a multitude of waves from the local radio stations, to internationals ones and even handheld portable 2-way radio signals. Radio waves are received at varying frequencies. Radio station frequencies are always measured in KiloHertz. On most shortwave radios you'll find toggles where you can flip from one band to another. What are the different types of bands and what do they stand for. Here's a quick summary:

SW - Shortwave
Most shortwave radios, whether small portable ones or larger tabletop radios, usually have up to 13 different channels. Shortwave frequencies go from 350KHz to 30,000KHz and are picked up from all parts of the world. Because shortwave transmission operates off waves reflected from the earth's ionosphere (which has to do with activity on the sun), shortwave channels are not always stable. A station mat be on one frequency at midday and on another in the evening. Higher end shortwave radios usually come with a small booklet or guide to shortwave channels. There are also downloadable lists and programming guides available on the Internet.

MW/AM
The Medium Wave (MW) band is an internationally agreed band of frequencies (530-1710KHz) primarily set aside for the purpose of broadcasting. It is also known as the AM (Amplitude Modulation), MF band, or the Broadcast Band (BCB) in various parts of the world. There are stations using this band in every continent. In the USA alone there are about close to 5500 stations on 106 channels in the AM band. All shortwave radios can receive these waves.

FM
FM (76-108MHz) stands for frequency modulation. FM is used by local radio stations. FM frequencies generally have less greater interference and static. All shortwave radios can receive these waves.

LW
Long Wave (LW) (150-529KHz) is only used by broadcasters in Europe, North Africa, Mongolia and the Asian part of the former Soviet Union. In other parts of thw world, frequencies in this band may be used mainly by navigational beacons.

SSB
SSB stands for "Single Side Band". This particular band is not a carrier of frequencies but rather a derivative of them, hence it's name "side". If we took one AM frequency and dissected it, we'd find that it consists of even more bands, in fact two: USB (Upper Side Band) and LSB (Lower Side Band). Not all shortwave radios can receive SSB signals. If your shortwave radio doesn't read SSB, then when you tune to a channel that's transmitting on this band, what you hear will not be understandable. This channel usually permits reception of amateur radio and military/commercial/maritime communication. High-end shortwave radios have the ability to receive SSB signals.

Shortwave radios come in various sizes and with a number of different functions. There are differences in tuning, saved presets, and extra features as well.

Tuning
Shortwave radio tuning can be either digital or analog. Radios with analog tuning have the traditional turning knob that you turn to lock onto a radio station. More sophisticated and pricier models have digital tuning capabilities. Digital tuning is usually more precise. Most shortwave radios that use digital tuning use a technology called PLL or Phase Locked Loop, which improves tuning precision on radios. Shortwave radios with digital tuning have additional helpful features like channel scanning and lock. Channel scanning is a mode that will literally scan the channels that your receiver is able to catch one by one.

Memory Preset Tuning
Because there are so many shortwave channels, most shortwave radios come with the ability for you to program an average of 40 channels. Higher end models can have up to 162 channel preset capabilities. Some are actually factory programmed with stations already preset. You switch between preset channels using buttons located on the radio.

Station Labels
This is a feature only available with shortwave radios that have digital tuning. Some radio models may come with station labels, which are actually names rather than a frequency reading. SO instead of saying 9410, it would say "BBC News". On some radios this feature is editable, which means you can change the title at anytime.

World Time Clock
Since most shortwave radios are used to tune into foreign radio stations around the world, many have built-in world time clocks where you can view the current time in various international countries.

Interference Reducers
Many shortwave radios have special built-in technology that works to eliminate interferece. During tuning, PLL or Phase Locked Loop helps improve tuning and precision on radios. Continuous Coverage is another feature that tunes all shortwave bands constantly. Synchronous Detection Circuitry also helps to make your shortwave radio stations sound clear.

Alarms & Sleep Timers
Many more sophisticated usually portable shortwave radios alarm clocks that you can wake up to. You can set your alarm to whatever time and have it wake you up with the station of your choice. Some shortwave radios also give you the choice of waking up to various tones too. Some even have sleeps timers, which give you the ability to program the radio to shut off after a certain period of time.

Virtually all shortwave radios have headphone jacks. Some may also have optional ports for additional antennas and RCA audio out ports for recording from these radios.

Many handheld and portable shortwave radios operate on alkaline batteries. Many also have an optional AC power connection.