A wireless link budget is the directional sum of every gain and loss from a named transmitter reference plane to a named receiver input; link margin is expected received power minus the receiver level required for the stated performance. Include conducted output, transmit feeder and connector loss, transmit antenna gain, path loss, polarization and pointing loss, receive antenna gain, receive feeder loss and the required receiver input. Keep free-space loss, rain, clear-air multipath, diffraction, obstruction, interference and equipment tolerance as separate rows.
For example, +30 dBm conducted power, 1.5 dB transmit loss, 34 dBi transmit gain, 129.6 dB free-space loss, 34 dBi receive gain and 1.5 dB receive loss produce about -34.6 dBm at the receiver input. Against a -70.5 dBm requirement, the arithmetic margin is 35.9 dB. Do not call all 35.9 dB fade margin until the project has applied the approved rain, multipath, clearance, pointing, polarization, interference and tolerance model.
Reject a budget that mixes typical and worst-case values, combines directions, hides reference planes or treats a regulatory EIRP ceiling as guaranteed radiated power. Required inputs are frequency, distance, path profile, antenna heights and patterns, feeder construction, polarization, climate, availability target, waveform, bandwidth, receiver criterion and coexistence environment. The final evidence should include the calculation revision, source of each value, installation measurements and the method used to predict outage.