A simple, reusable link budget structure. Work in dB and keep every assumption visible.

Transmit side
- Transmitter output power (dBm), at the PA output.
- Minus transmit losses: filter, cable, connectors (dB).
- Plus transmit antenna gain (dBi).
= EIRP (dBm). Check it against regulatory limits.

Path
- Free-space path loss: FSPL(dB) = 20*log10(d_km) + 20*log10(f_MHz) + 32.44.
- Plus additional losses: atmospheric gases, rain (for higher frequencies), foliage, building penetration, polarization mismatch, pointing loss.
- Plus a fade margin appropriate for the required availability.

Receive side
- Plus receive antenna gain (dBi).
- Minus receive losses before the LNA.
= Received signal power (dBm).

Noise and sensitivity
- Thermal noise floor: -174 dBm/Hz at 290 K, plus 10*log10(bandwidth in Hz).
- Plus receiver noise figure (dB).
- Plus required SNR for your modulation, coding and target error rate.
= Receiver sensitivity (dBm).

Link margin = received power - sensitivity. Positive margin with appropriate fade margin means the link should close.

Common mistakes
1. Mixing dBm and dBW.
2. Using the wrong bandwidth (occupied bandwidth versus noise bandwidth).
3. Forgetting implementation losses in the modem (real demodulators need more SNR than theoretical curves).
4. Ignoring the Fresnel zone. Line of sight is not enough; the first Fresnel zone should be largely clear of obstructions, or diffraction losses apply.
5. Treating fade margin as optional for outdoor links.

Post your link budgets here for review; include frequency, distance, antennas and the modulation you plan to use.