[SADXA] Optimum GreyLine-Termination Angle for VK0EK (Heard) / AZ Propagation

[W7EXG (Bill)]

By now, most of us have recognized the two opportunities per day, for
propagation between AZ and VK0EK, due to the Greyline.  

QRZ bearing data shows 186 deg Short Path (SP) (6 deg Long Path (LP))

The question becomes: Is this geometrical bearing, the correct bearing when
Greyline propagation is being considered? I submit the correct answer is..
Not Always. 

For April 4th, 0140Z UTC, the greyline passing through Tucson, also passes
slightly West of Heard Island. The Greyline Terminator line is along the 7
deg / 187 deg line. It is almost the perfect storm, since the Greyline
propagation path is close to the required 186 deg SP bearing. As most of us
know, the evening propagation for VK0EK has recently been exceptional. 

(HEARD considering staying put!)

However, for April 4th, 1300Z UTC, the greyline passing thought Tucson,
passes significantly more West of Heard Island. In this case, the Greyline
Terminator line is along the 353 deg and 173 deg line.

This suggests the morning propagation may be best at a SP bearing of 173
degrees, not 186 degrees (a 13 deg bearing difference) 

Because of the further west Greyline for HEARD, and an indirect propagation
path, this suggests the AM propagation between AZ and HEARD may currently
not be as good as in the PM. 

This analysis is based on the greyline prediction websites.. some of which,
may not yield identical results. The link below is easy to use, and will
verify my analysis above. It agreed with several others greyline predictors
I tried.

https://academo.org/demos/day-night-terminator/

73s, and good luck with HEARD!

Bill W7EXG