The Radio Wave

The basic building block of radio communications is a radio wave. Like waves on a pond, a radio wave is a series of repeating peaks and valleys. The entire pattern of a wave, before it repeats itself, is called a cycle. The wavelength is the distance a wave takes to complete one cycle. The number of cycles, or times that a wave repeats in a second, is called frequency. Frequency is measured in the unit hertz (Hz), referring to a number of cycles per second. One thousand hertz is referred to as a kilohertz (KHz), 1 million hertz as a megahertz (MHz), and 1 billion hertz as a gigahertz (GHz). The range of the radio spectrum is considered to be 3 kilohertz up to 300 gigahertz.

A radio wave is generated by a transmitter and then detected by a receiver. An antenna allows a radio transmitter to send energy into space and a receiver to pick up energy from space. Transmitters and receivers are typically designed to operate over a limited range of frequencies.

Radio waves travel in waves, much like the waves of the ocean. They move (or oscillate) up and down in a uniform motion. Just imagine for a moment if you held a piece of string in your hands with one end in each hand and you pulled it apart tightly. The string would move up and down rapidly, and this is very similar to how radio waves oscillate through the air. The amount of time it takes for the string, or a radio wave, to move from its top position to its bottom position and up again to its original position is called its cycle. The amount of distance that a radio wave moves in one cycle is called its wavelength. The number of cycles in one second is the radio wave’s frequency.

Factors Associated With The Transmission of Radio Waves

One of the most important concepts for all ham radio operators is propagation. Propagation is the process of radio signals traveling through the air, bouncing from surface to surface as it travels to radio antennas. Hams will closely monitor the atmosphere for storms, weather conditions, solar flares, and other atmospheric conditions that affect the transmission of radio signals (or the propagation of radio signals) through the air. Weather can play a very important role in the effectiveness of a radio signal, and this is an especially important concern for those ham radio operators who engage in professional emergency services. Having the right antenna is an especially important concern for most radio operators.

The Radio Spectrum

The radio spectrum is the small section of the Electromagnetic Spectrum devoted to radio transmission. When you tune your radio to a specific station, you are choosing a specific frequency that is contained within the radio spectrum. All of these different frequencies are grouped together into specific types of frequencies, and these groupings are called bands. So, for example, there is the AM band, which contains signals from AM radio stations. Bands are a very important concept in ham radio so we will look at the four main segments (or bands) of frequencies.

• Shortwave or High Frequency Radio waves traveling in this band are intended for AM radio stations, “ship-to-shore” and “ship-to-ship” communication, several military frequencies, the Citizens Band, and several different ham radio bands are contained within this band.
• Very High Frequency (VHF) This band includes television channels 2 through 13, all FM radio stations, several ham radio bands, some military frequencies, and some other commercial radio frequencies.
• Ultra High Frequency (UHF) This band includes TV channels 14 and higher, two Ham radio bands, cell phones, and some military frequencies.
• Microwave This band includes GPS signals, wireless telephones, WiFi networking signals, several ham radio bands, and, yes, your microwave oven.

The Transceiver

What EMS personnel would typically refer to as a radio would actually be called a transceiver. A piece of equipment that receives a radio signal and outputs the signal to a speaker (also commonly referred to as a radio) is a receiver. A transmitter is a device that generates radio waves. When you put the two together, you get a ‘transceiver’.

History of Public Safety (Police) Radio