Deploying Point-to-Point Wireless Links: Page 4 of 8

Gain in point-to-point systems is a product both of radio output power and of an antenna's ability to focus that power. All other things being equal, higher gain systems are more difficult to build. Because all RF signals experience predictable loss over distance, you might logically assume those that operate over longer distances will need more gain. However, transmission is only one side of the coin. A system's receive sensitivity is equally critical. And as you probably guessed, more sensitive receivers are most costly to build.

In deploying a point-to-point system, you'll often be working with a loss budget. Loss in RF systems begins at the output of the radio transmitter and continues through to input of the receiver. Free space loss, also known as path loss, occurs as signals pass through the air, mainly because radio signals spread over distance, somewhat like water exiting a garden hose. As frequency increases, so too does path loss, meaning a 2.4-GHz system will have a greater range than that of a 5-GHz system of equal power output. For a frame of reference, note that a 2.4-GHz radio signal will experience a free space path loss of about 120 dB over a distance of 5 miles. (For a free space loss calculator, see "Free Space Loss.")