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FA Cup
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F region
F region


noun 
Definition:
 
highest part of Earth's atmosphere: the highest part of the ionosphere that reflects high-frequency radio waves. It is divided into two layers, the F1, which extends upwards from 180 km (112 mi) and is present only during the day, and the F2, extending upwards from 300 km (186 mi).
Encarta® World English Dictionary [North American Edition] © & (P)2009 Microsoft Corporation. All rights reserved. Developed for Microsoft by Bloomsbury Publishing Plc.
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