Radio waves in the ionosphere

1. When a radio wave leaves a transmitting antenna, it travels in all directions. 2. One part of the signal travels along the ground and is called the ground wave. 3. The second part of the signal travels through the lower atmosphere in a direction parallel to the ground. 4. Another part travels at an angle to the ground. 5. The part travelling through the lower atmo­sphere is called the tropospheric wave; the part travelling at an angle to the ground — the ionospheric wave.

6. In the high-frequency part of the radio spectrum — 3—30 megacycles (mc) — the ground and tropospheric wave compo­nents travel short distances, not more than 25 or 30 miles. 7. The ionospheric wave component of the signal can travel to great distances, making long-distance short-wave communication possible.

8. While leaving the transmitting antenna, the ionospheric wave starts travelling and reaches a region called the iono­sphere. 9. This region begins at a height of about 60 miles above the ground. 10. On reaching the ionosphere, radio waves supply the free electrons of the region with electromagnetic energy. 11. As a result, the free electrons start vibrating and radiate this energy.

12. The ionosphere is formed primarily by ultraviolet radia­tion reaching it from the Sun. 13. As this radiation interacts with the gases in the upper atmosphere, these gases, which con­sist mainly of neutral molecules, absorb the ultraviolet energy, and in the process lose an electron. 14. This process leaves free electrons and positively charged gas molecules, which are called ions. 15. The formation of ions is called ionization.

16. The ionosphere has the property of bending radio waves and returning them to the ground at considerable distances from the point of transmission. 17. Bending may change the direction of the wave and it is returned to the ground at some distant point.

18. The ionosphere is not a single¹ region; it consists of several layers and the properties of these layers vary, depend­ing on many factors. 19. One of the layers, the F-layer², is of primary importance. 20. Most of the world's long-distance high-frequency communication takes place by means of reflec­tion of radio waves from this region. 21. The F-layer is at the height of about 175 miles.

22. Radio signals from the F-layer may be returned to the ground at distances as great as 2,000 miles from the transmitter.

Пояснения к тексту

1. single — зд сплошной

2. the F-layer — слой F ионосферы

Слова для запоминания

п height [hait], layer

и bend (bent), interact, lose (lost), supply

a distant, low, upper

ado mainly.