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NineEighteen
21st Apr 2003, 21:16
An aircraft is using a night time HF frequency of 5.5 MHz with ATC. The frequency the pilot would expect to use by day is:

a. 3 MHz
b. 12 MHz
c. 15 MHz
d. 18 Mhz

The correct answer is b. I can see why the freq needs to be higher by day but why 12 MHz specifically? Why not 15 MHz or 18 MHz? Is it just that the answer is most likely to be the lowest, higher frequency than 5.5 MHz or is there a relationship I should know about?

Thanks in advance
9:18

Alex Whittingham
21st Apr 2003, 21:21
There is a rough relationship, day frequencies are roughly twice night-time frequencies.