The decision you should be able to make
Predict received power and compare it with the requirement for the selected operating mode.
Core engineering
A basic budget is Pr = Pt – Ltx + Gtx – Lpath + Grx – Lrx. Add other mechanisms as explicit losses or statistical allowances rather than silently changing FSPL.
Receiver sensitivity is conditional on bandwidth, modulation/coding, error criterion and sometimes temperature. Use the threshold for the mode needed to meet the service target.
Integrated outdoor radios may have negligible RF feed length, while connectorised systems need actual cable, connector, radome, branching and surge-device losses at frequency.
Link margin for a chosen mode = predicted received power – required receiver threshold for that mode.
Example: 20 dBm transmit, 25 dBi antennas at both ends, 2 dB terminal loss at each end and 127.7 dB FSPL gives about -61.7 dBm before other impairments. Against a -75 dBm mode threshold, the provisional margin is 13.3 dB.
Equipment and field checks
- Check conducted-power limits and automatic power reduction for the chosen mode and channel width.
- Use antenna gain and cable loss at frequency, including both polarisation chains where relevant.
- Record firmware and data-sheet versions because thresholds and permitted modes can change.
Do not progress until
Every budget line has a sign, unit, reference point and evidence source; measured commissioning RSSI will later be compared with the prediction.
Limits and cautions
- Do not apply one universal minimum margin to every path. Convert the service target through the applicable propagation method.
Primary sources
Sources were checked for this technical review. Recheck regulator and equipment requirements at the point of design or installation.