Which filter is typically range-limited to about 4 nautical miles?

• A. FTC
• B. STC, generally to a range of 4 nm
• C. Both STC and FTC
• D. Neither STC nor FTC

Answer: (B)

This question is about how radar display filters affect how far you can reliably see targets. The short time constant filter uses a small averaging window, so it responds quickly and helps suppress near clutter. But because it doesn’t integrate signal over a longer period, weak echoes from distant targets don’t stand out as well, effectively limiting the usable display range. In typical radar setups, that limit is around four nautical miles. If you needed to see farther targets, you’d use a longer integration filter (the fixed time constant), which improves distant detection but can smear or delay results for close or fast-moving targets. So the short time constant filter is the one typically range-limited to about 4 nm.