radiation in question. This step may not be required if adequate systemic link budgets are achieved. Simplifications needed Often link budget equations are messy and complex, so standard practices have evolved to simplify the Friis transmission equation into the link budget equation. It includes the transmit and receive antenna gain, the free space path loss and additional losses and gains, assuming line of sight between the transmitter and receiver. The wavelength (or frequency) term is part of the free space loss part of the link budget. The distance term is also considered in the free space loss. Transmission line and polarization loss In practical situations (deep space telecommunications, weak signal DXing etc.) other sources of signal loss must also be accounted for The transmitting and receiving antennas may be partially cross-polarized. The cabling between the radios and antennas may introduce significant additional loss. Fresnel zone losses due to a partially obstructed line of sight path. Doppler shift induced signal power losses in the receiver. Endgame If the estimated received power is sufficiently large (typically relative to the receiver sensitivity), which may be dependent on the communications protocol in use, the link will be useful for sending data. The amount by which the received power exceeds receiver sensitivity is called the link margin. Equation A link budget equation including all these effects, expressed logarithmically, might look like this: where: , received power (dBm) , transmitter output power (dBm) , transmitter antenna gain (dBi) , transmitter losses (coax, connectors...) (dB) , path loss, usually free space loss (dB) , miscellaneous losses (fading margin, body loss, polarization mismatch, other losses, ...) (dB) , receiver antenna gain (dBi) , receiver losses (coax, connectors, ...) (dB) The loss due to propagation between the transmitting and receiving antennas, often called the path loss, can be written in dimensionless form by normalizing the distance to the wavelength: (where distance and wavelength are in the same units) When substituted into the link budget equation above, the result is the logarithmic form of the Friis transmission equation. In some cases, it is convenient to consider the loss due to distance and wavelength separately, but in that case, it is important to keep track of which units are being used, as each choice involves a differing constant offset. Some examples are provided below. (dB) ≈ 32.45 dB + 20 log10[frequency (MHz)] + 20 log10[distance (km)] (dB) ≈ −27.55 dB +