The decision you should be able to make
Read a radio or antenna data sheet and identify the values that belong in a link budget.
Core engineering
Wavelength is lambda = c/f. A higher frequency means a shorter wavelength, but it does not by itself guarantee a narrower beam. For the same physical aperture and efficiency, shorter wavelength permits higher gain and a narrower main beam.
Use 10 log10(P2/P1) for power ratios. Use 20 log10(E2/E1) only for field or voltage ratios under the same impedance. dBm is absolute power referenced to 1 mW; dBi is antenna gain relative to an isotropic radiator; dB is a ratio.
Received signal is useful only relative to the receiver requirement and the interference-plus-noise environment. Transmit power alone is not a measure of link quality.
Power in dBm = 10 log10(power in mW). A doubling of power is about +3.01 dB; a tenfold increase is +10 dB.
100 mW is 20 dBm. Adding a 23 dBi antenna does not create 23 dBm of transmitter power; it produces 43 dBm EIRP before transmit-side losses, which must then be checked against local rules.
Equipment and field checks
- Confirm whether each power figure is conducted power, EIRP, per-chain power or total power.
- Use gain at the actual operating frequency and the correct polarization, not a family headline value.
- Match PoE standard, voltage range, connector type, environmental rating and supported regulatory domain.
Do not progress until
Every value in the first budget has a unit, reference point and source data-sheet revision.
Limits and cautions
- This lesson uses far-field, narrowband link-budget concepts. Near-field coupling and complex indoor multipath require different treatment.
Primary sources
Sources were checked for this technical review. Recheck regulator and equipment requirements at the point of design or installation.