Topband: Rev C of the FT5ZM direction paper

Carl Luetzelschwab carlluetzelschwab at
Sun Mar 30 19:18:26 EDT 2014

Let me try this one more time.

In a personal e-mail W4ZV said that he believed my statement "For the
record, the apex is at the antipode of FT5ZM" is incorrect. The apex
referred to is where the sunrise terminator and sunset terminator intersect
in the USA. So I did what I should have done much earlier - I dug deeper
into DX Atlas and W6ELProp.

Bill is correct. Where I screwed up is two-fold: believing for a long long
time that the apex was always at the antipode but not checking this out,
and not understanding that DX Atlas and W6ELProp define sunrise and sunset
a bit differently.

DX Atlas defines sunrise/sunset when the top limb of the Sun is on the
horizon. W6ELProp defines sunrise/sunset when the center of the Sun is on
the horizon. This difference is 4-5 minutes, and makes a difference when
looking at this "black hole" scenario. When you use the same times in both
programs (not their respective sunrise/sunset times), they both give the
same answer.

The major characteristics of this issue are given in Rev C - along with
a note with respect to the real world.

Carl K9LA

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