Link budget

The transmission of power balance (English link budget ) is a measure of the quality of a transmission channel in communications technology. The balance sheet is Bel indicated in the unit and calculated in a simple model by adding the transmitter power, receiver sensitivity, antenna gain and free space loss.

The transmission of power balance can in Bel expressed adopt positive or negative values ​​.

Calculation

The power transfer balance sheet describes the received power at the receiver, benefits are expressed in dBm, relative to the output by the transmitter output power minus the various damping factors that describe the transmission channel. An exemplary power transfer balance can have the following form:

The directional characteristics of the receive and transmit Ante Call are as antenna gain entered with a positive sign, the remaining summands represent transmission losses are as the attenuation of connecting cables on reception and on transmission side. The term represents the free-space loss, this term is usually the largest in terms of value. All losses during propagation are summarized in the term path loss. These are in addition to the free space attenuation, especially absorption losses during the penetration of media (atmosphere), losses due to diffraction and shadowing as well as losses due to reflections within the Fresnel zone (as fading occurring ). All this in addition to free space attenuation occurring losses are summarized here.

The attenuation values ​​sweep usually several orders of magnitude, primarily due to the high free space attenuation. Power transfer balances with very large values ​​occur because of the large distances in interstellar communication systems or by the earth - moon - earth communication. In the last case, the free space attenuation to 250 dB, which must be compensated by antennas with correspondingly large gain, high transmit power and very sensitive receiver.