What is the approximate maximum fiber run length before signal dropout?

• A. 20 miles
• B. 26 miles
• C. 32 miles
• D. 40 miles

Answer: (B)

The key idea is link budget—how far a fiber signal can travel before the loss of signal strength causes dropout. As light moves through fiber, it loses power due to attenuation, and the receiver must still be able to decode the signal once the power drops to a minimum level. The farther you go, the more loss accumulates, so there’s a practical distance you can reach without adding repeaters or amplifiers.

Using a typical fiber attenuation value around 0.2 dB per kilometer for common long‑haul fiber, a run of about 42 kilometers (roughly 26 miles) accumulates enough loss to approach the limit where the receiver can no longer reliably detect the signal, even with some margin for noise. That makes 26 miles a reasonable approximate maximum for a repeaterless link in many broadcast setups. Shorter distances, like 20 miles, are well within the budget and safe; longer distances, such as 32 or 40 miles, would usually require amplification or repeaters to avoid dropout.