Review: Point-to-Point Systems: Page 12 of 15

Attenuation: The loss that occurs as a signal travels through a wire, free space or an object. Attenuators can be used to purposely decrease the power of a wireless signal. Attenuation is measured in dB (decibels).

dB (decibels): The unit of measurement for gain or loss in a wireless signal. dB is measured on a logarithmic scale--a 3 dB increase in gain doubles the power of a radio signal. A 10 dB increase in gain increases the power tenfold.

Diffraction: Describes the bending of an RF wave as it hits an object. Diffraction is different than refraction--diffraction describes waves bending around an obstacle, while refraction describes waves bending due to an object's different density as the wave passes through it.

Fade margin: The extra signal, factored into a wireless link budget, beyond the receive sensitivity to allow for a wireless link to operate reliably. As the distance of a wireless link increases, there is a greater chance for loss to be introduced into the signal, so a greater fade margin should be budgeted for.

Free space loss: The predictable decrease in power of a wireless signal as it travels through the air. Free space loss is measured through a logarithmic equation (calculators are available on the Web to determine free space loss).