Radar Observer · Limitations — Second-Trace Echoes
Second-trace (multiple-trace) echoes occur under anomalous propagation when:
- AA distant target's echo returns after the next pulse is transmitted, so it plots at a false (shorter) range✓ Correct
- BRain absorbs the signal
- CThe heading marker is misaligned
- DGain is set too low
Explanation
When super-refraction lets the beam reach beyond the set's nominal range, a far target's echo can arrive after the following pulse has gone out, so the set displays it at a much shorter (wrong) range. Changing the PRF/range scale makes a second-trace echo move or vanish, distinguishing it from a real target.
Authority: Bowditch (Pub. No. 9), Radar Limitations
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