130:, during high solar activity periods can refract and thus block signals of up to about 15 MHz from reaching the F1 and F2 regions, with the result that distances are much shorter than possible with refractions from the F1 and F2 regions. But extremely low radiation-angle signals (lower than about 6 degrees) can reach distances of 3000 km (1900 miles) via E region refractions.
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74:. It acts as a dependable reflector of HF radio signals as it is not affected by atmospheric conditions, although its ionic composition varies with the sunspot cycle. It reflects normal-incident frequencies at or below the
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The F1 layer is the lower sector of the F layer and exists from about 150 to 220 km (100 to 140 miles) above the surface of the Earth and only during daylight hours. It is composed of a mixture of molecular
99:(at ~90 km, 56 miles). This atomic oxygen provides the O atomic ions that make up the F2 layer. The F1 layer has approximately 5 × 10 e/cm (free electrons per cubic centimeter) at noontime and minimum
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layer has about 10 e/cm. However, variations are usually large, irregular, and particularly pronounced during magnetic storms. The F layer behaviour is dominated by the complex thermospheric winds.
43:, while 'region' is the volume that contains the said layer. The F region contains ionized gases at a height of around 150–800 km (100 to 500 miles) above sea level, placing it in the Earth's
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and NO, and atomic ions O. Above the F1 region, atomic oxygen becomes the dominant constituent because lighter particles tend to occupy higher altitudes above the
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activity, and increases to roughly 2 × 10 e/cm during maximum sunspot activity. The density falls off to below 10 e/cm at night.
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layer. However, this depends upon the frequency of a propagating signal. The E layer electron density and resultant MUF,
55:, where chemical composition varies with height. Generally speaking, the F region has the highest concentration of free
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Though fairly regular in its characteristics, it is not observable everywhere or on all days. The principal
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television and FM radio signals being received over great distances, well beyond the normal 40–100
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layer exists from about 220 to 800 km (140 to 500 miles) above the surface of the Earth. The F
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anywhere in the atmosphere. It may be thought of as comprising two layers, the F1 and F2 layers.
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during the summer for paths of 2,000 to 3,500 km (1200 to 2200 miles) is the F
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78:(approximately 10 MHz) and partially absorbs waves of higher frequency.
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Ionospheric
Propagation, Transmission Lines, and Antennas for the QRP DXer
39:. As with other ionospheric sectors, 'layer' implies a concentration of
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layer frequencies are the frequencies that will not go through the F
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during both day and night. The horizon-limited distance for one-
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70:(formerly the Kennelly-Heaviside layer) and below the
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is home to the F layer of ionization, also called the
248:, Milliwatt QRP Books, 2011, pp. 1-16, 1-22 to 1-24.
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is usually around 4,000 km (2500 miles). The F
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259:"Near-Real-Time F2-Layer Critical Frequency Map"
164:
141:layer is the principal reflecting layer for HF
212:Kamide, Yohsuke; Chian, Abraham C.-L. (2007).
216:Handbook of the solar-terrestrial environment
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35:and New Zealand physicist and meteorologist
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66:The F-region is located directly above the
177:layer. Under rare atmospheric conditions,
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323: This article incorporates
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336:General Services Administration
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31:, after the English physicist
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261:. spacew.com. Archived from
220:. Berlin: Springer. p.
165:Usage in radio communication
47:, a hot region in the upper
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363:Radio frequency propagation
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291:Cambridge University Press
286:The Electronics of Radio
181:can occur, resulting in
128:maximum usable frequency
111:layer merges into the F
331:Federal Standard 1037C
325:public domain material
29:Appleton–Barnett layer
283:Rutledge, D. (1999).
143:radio communications
193:) reception area.
16:Layer in ionosphere
293:. pp. 2–237.
76:critical frequency
51:, and also in the
231:978-3-540-46315-3
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37:Miles Barnett
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340:the original
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304:. Retrieved
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267:. Retrieved
263:the original
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53:heterosphere
45:thermosphere
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154:propagation
358:Ionosphere
352:Categories
306:2014-12-07
269:2014-12-07
200:References
169:Critical F
97:turbopause
49:atmosphere
25:ionosphere
57:electrons
68:E region
21:F region
101:sunspot
23:of the
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41:plasma
327:from
187:miles
133:The F
107:The F
295:ISBN
226:ISBN
89:ions
61:ions
59:and
19:The
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183:VHF
147:hop
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91:O
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