Embedding information in energy emissions

Anything where a disturbance can be introduced, which then propagates away from the source, opens the possibility of using these for communication purposes if it can be received and interpreted again. Sound is the easiest to understand where varying lengths and intensities of air passing over our vocal cords cause vibrations at different rates and intensities, or frequencies and loudness to put it plainly. The varying intensity and frequency of sound waves are what we use to embed information in through words and sentences (which are just a combination of these two) and our ears are then able to receive these signals which we can understand.

Frequency and wavelength

As with the sound example, frequency is the term which describes the rate of oscillation of a disturbance per second. It has been referred to in cycles per second before, but the name universally accepted now is named after Heinrich Rudolf Hertz who was the first person to provide conclusive proof of the existence of electromagnetic waves. The symbol is Hz, and 1 Hertz means 1 cycle or oscillation per second.

The wavelength of a wave is the distance between two crests of the wave, or a full cycle of the wave as determined by the frequency of the wave, as well as the medium through which it is travelling. A average wavelength of a wave at sea varies between 200 – 400 ft, whereas the wavelength of a sound wave in air of a 350 Hz tone is 3ft.

Electromagnetics

Another form of disturbance and propagation model we have is electromagnetic fields. Here, a disturbance propagates away from the source at the high rate of 186 000 miles per second, and therefore this would make for an excellent communications model as almost instantaneous transmission over great distances becomes a possibility. This speed is actually the speed of light, and light itself was the first form of electromagnetic radiation used for communication purposes.

What is electromagnetic radiation

Electromagnetic radiation is the emission of energy in the form of electric and magnetic fields moving outward from the source at the speed of light. It is created by generating a time varying potential difference across a gap, and more specifically an antenna is designed to transition this energy from travelling inside a transmission line into the air. Electromagnetic radiation also has the characteristics of frequency, intensity, and wavelength.

In the formation region of an antenna where these travelling waves are created the relationship between the Electric fields and the Magnetic fields are not yet regular and high concentrations of either exist along the surface of the antenna in this formation region, this is known as the near-field. The formation area, or near-field about an antenna is typically in the order of 2 wavelengths so on a FM transmitter at 100 MHz, the wavelength is 9 ft, so being closer than 18 ft or 6 m from a single element FM antenna means you are in this formation zone where the levels of the E fields and H fields are not related as they would be a long distance off.

Radio frequency radiation (RF)

Radio frequency radiation is then the portion electromagnetic radiation, which is used for telecommunications purposes, and as a result has become an integral part of our daily lives and the global economy.

Hazards associated with RF radiation

As RF radiation is a form a travelling energy, its ability to interact with a person’s body and cause heating means exposure to high levels thereof needs to be limited and is controlled by legislation laid down by governing bodies globally.

Staying safe when working around transmitting antennas and sources of RF mandate that the field intensity, both the Electric, and Magnetic fields are correctly assessed, especially in the formation zone (near-field) in terms of safe working limits and sufficient warning must be given to the user.

The devices designed to do this are called personal RF monitors, and in order to be effective they must measure the Electric and Magnetic field over the range of operation, and report this in terms of percentage of the actual allowable exposure with 100% indicating the maximum permissible levels. The fieldSENSE60 is one such tool which has specifically been designed with telecommunications workers and those coming near transmitting antennas in mind.