Link budget

+ transmitter output power - transmitter cable and connector loss + transmitter antenna gain - free space loss + receiver antenna gain - receiver cable and connector loss

Cables reduce the link budget by dissipating power. Manufacturers rate cable loss in decibels per foot. Power is also lost through connectors, and these too are rated by their manufacturers.

The sending and receiving antennae add to the link budget. They do so by focusing power, not by amplifying it.

The largest loss in most wireless links will be due to the free space between the antennae. The greater the distance and the higher the frequency, the greater the loss. The power drops with the square of the frequency and the square of the distance. Doubling the distance or the frequency will cut power by a factor of four.

A link will succeed if the total loss does not exceed the sensitivity threshold of the receiving radio.

You can calculate link budgets using this calculator. (Note that the calculator is an Excel spreadsheet that you can download for use off line).

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