---
title: "Skip zone"
subject: "Propagation and Antenna"
chapter: 4
key: "semester_6/propagation_and_antenna:skip-zone"
source: https://www.bctengineer.com/q/semester_6/propagation_and_antenna/skip-zone
site: BCT Engineering
---

# Skip zone

Propagation and Antenna · Chapter 4: Propagation and Radio Frequency Spectrum

- Asked in: 2072 Magh, 2 marks
- Video: [The Skip Zone](https://www.youtube.com/watch?v=C1kglBuZKHk) — Stan Gibilisco
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/propagation_and_antenna/skip-zone
- Whole chapter: https://www.bctengineer.com/md/semester_6/propagation_and_antenna/chapter-4

## Question

Explain skip zone for ionospheric region.

## 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.

## Answer

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.

```text
  ~~~~~~~~~~~~~~~/\~~~~~~~~~~ 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).

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. The skip zone lies between:
   A. The transmitter and the antenna base
   B. The end of the useful ground wave and the point where the first sky wave returns
   C. The ionosphere and the earth
   D. Two sky-wave hops
   Answer: B. No usable signal is received between ground wave end and the skip distance. (Key point: Definition)

2. Why does a skip zone exist at HF?
   A. Ground wave dies within tens of km and steep rays above fc penetrate the ionosphere
   B. The D layer absorbs ground waves
   C. The earth is flat
   D. Atmospheric noise is high
   Answer: A. For f > fc steep rays go through the layer, so sky waves land only beyond the skip distance. (Key point: Why it exists)

3. How does the skip zone change with frequency?
   A. It shrinks as frequency rises
   B. It grows as frequency rises
   C. It is independent of frequency
   D. It vanishes above fc
   Answer: B. Higher frequency needs a larger angle (longer path) to be refracted, so the skip zone grows. (Key point: Size variation)

## Related in Propagation and Antenna

- [Critical frequency](https://www.bctengineer.com/question.md?key=semester_6%2Fpropagation_and_antenna%3Acritical-frequency) — Propagation and Antenna, chapter 4, asked 2×

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- [Oxidation pond for Terai town, 12,000](https://www.bctengineer.com/question.md?key=semester_6%2Fsanitary_engineering%3Aoxidation-pond-terai-12000) — Sanitary Engineering, chapter 7