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Skip zone

Short answer

Skip zone is the silent region between the end of ground-wave coverage and the first sky-wave return where no signal is received. It occurs at HF because ground wave dies quickly while steep rays penetrate the ionosphere; its size increases with frequency.

Explain skip zone for ionospheric region.

The skip zone (silent zone) is the region around a transmitter, between the point where the ground wave becomes too weak and the point where the first sky wave returns (the skip distance), in which no usable signal is received.

  ~~~~~~~~~~~~~~~/\~~~~~~~~~~ ionosphere
                /  \
   ground wave /    \
  Tx~~~~~~>   /      \  sky wave lands
  ==|=====|=========|==========
     ground  skip     reception
     wave    zone

It exists because, for f > fc, steep rays penetrate the ionosphere, while the ground wave at HF dies within a few tens of km. Its size grows with frequency and shrinks when fc is high (daytime).

✓ Answer checked by Claude Opus 5.5 (high effort)

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