Radio Frequency (RF) Technologies
RF fundamentals
RF is alternating electromagnetic energy. Frequency and wavelength are inversely related (λ = c / f): about 12.5 cm at 2.4 GHz and 6 cm at 5 GHz. Candidates must name the propagation behaviors - absorption (water, foliage), reflection (metal, glass), scattering (small or rough objects), refraction (bending through density changes) and diffraction (bending around obstructions) - and recognize that multipath produces both diversity gain and intersymbol interference.
Power math
Everything is logarithmic. ±3 dB doubles or halves power; ±10 dB is a factor of ten; +6 dB roughly doubles free-space distance. dBm is absolute, dBi/dBd are relative, and dBi = dBd + 2.14. EIRP = transmit power + antenna gain − cable and connector loss. A link budget adds gains and subtracts losses to predict RSSI at the client.
Noise, SNR and modulation
Noise floor is the denominator of SNR: a −65 dBm signal over a −95 dBm noise floor is 30 dB SNR, enough for high MCS rates. Doubling channel width raises the noise floor about 3 dB. Higher-order modulation (up to 1024-QAM) demands more SNR; OFDM subcarriers, OFDMA resource units and MIMO spatial streams convert SNR into throughput.
Traps
Confusing dB, dBm and dBi; omitting cable loss from EIRP; believing a 6 dB increase comes from doubling transmit power (doubling is 3 dB); and treating free-space path loss as frequency-independent when it rises with frequency.
Rule of thumb
A 6 dB increase in path loss halves usable range at the same data rate; dropping one MCS step costs roughly 3–6 dB.