Link Budget - in Radio Systems

In Radio Systems

For a line-of-sight radio system, the primary source of loss is the decrease of the signal power due to uniform propagation, proportional to the inverse square of the distance.

• Transmitting antennas are for the most part not isotropic aka omnidirectional.

• Completely omnidirectional antennas are rare in telecommunication systems, so almost every link budget equation must consider antenna gain.

• Transmitting antennas typically concentrate the signal power in a favoured direction, normally that in which the receiving antenna is placed.

• Transmitter power is effectively increased (in the direction of highest antenna gain). This systemic gain is expressed by including the antenna gain in the link budget.

• The receiving antenna is also typically directional, and when properly oriented collects more power than an isotropic antenna would; as a consequence, the receiving antenna gain (in decibels from isotropic, dBi) adds to the received power.

• The antenna gains (transmitting or receiving) are scaled by the wavelength of the radiation in question. This step may not be required if adequate systemic link budgets are achieved.