Why Coaxial Cable Attenuation Skyrockets with Frequency
RF attenuation in coaxial transmission lines is governed by two physical mechanisms:
- Conductor Copper Loss (Skin Effect): At radio frequencies, electrons do not travel through the core of the wire; they crowd into an ultra-thin microscopic skin on the outer perimeter. Resistance increases with the square root of frequency ((sqrt{f})).
- Dielectric Loss: Molecular friction in the insulating foam or solid polyethylene jacket absorbs RF energy and turns it into thermal heat. Dielectric loss scales linearly with frequency ((f)).
The Standard Attenuation Equation
Coax manufacturers publish empirical coefficients (k_1) (resistive) and (k_2) (dielectric):
Loss_per_100ft (dB) = k1 × √f_MHz + k2 × f_MHz
The Trap of Thin RG-58 at UHF & Wi-Fi
Thin RG-58 cable has acceptable loss on 7 MHz HF (approx 1.2 dB/100ft). But if you run 100 feet of RG-58 to a 440 MHz UHF antenna, the loss exceeds 10.6 dB! That means over 91% of your transmitter power is incinerated as heat in the coax, leaving only 9% to radiate from the antenna!