In what units is RF feed line loss usually expressed?

RF feed line attenuation (loss) is universally specified by cable manufacturers using decibels (dB), which is a logarithmic unit that accurately reflects power ratios. In the US, the standard distance used for these specifications is 100 feet. While you will frequently see Ohms used in relation to coaxial cables, Ohms measure characteristic impedance (such as 50-ohm or 75-ohm coax), not signal loss. Decibels per 100 feet provides a standardized way to compare the efficiency of different cables at various frequencies. Distractors using 1,000 feet are incorrect for RF cables, though that length is commonly used when specifying the DC resistance of bulk electrical wiring.