Question
Which of the following paths is most likely to support long-distance propagation on 160 meters?
Answer Options
- A) A path entirely in sunlight
- B) Paths at high latitudes
- C) A direct north-south path
- D) A path entirely in darkness
Correct Answer: D
Explanation
The 160-meter band (1.8 MHz) is the lowest HF band and is extremely sensitive to atmospheric absorption, especially in the D-layer of the ionosphere. The D-layer, located roughly 50 to 90 km up, is heavily ionized by sunlight and is the primary cause of signal absorption on all HF bands during the day, with the effect being most pronounced at 160 meters.
Since the D-layer ionization vanishes almost completely shortly after local sunset, absorption is dramatically reduced. Therefore, the path most likely to support long-distance propagation on 160 meters is a path entirely in darkness. This requirement limits 160m DX to nighttime hours, when the signal can reach the higher F-layers for long-distance skip without being absorbed in the D-layer.
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