TopBand: Stew Perry Contest Distance Calculations

[Earl W Cunningham]

The 3rd annual Stew Perry Topband Distance Challenge contest is almost
upon us.  Tree, N6TR, who will be scoring the logs, will be using the
same accurate ellipsoidal Earth algorithm for calculating QSO distances
as I use in my program DBGRID.

For those of you who wish to calculate youir scores before submitting
your logs, you may e-mail me direct with your request for DBGRID for a
free copy.

Logically, it would seem best to calculate the distance between the
centers of the 4-character grid squares, however Tree will score the logs
by calculating the distance between the centers of subsquares "LL", which
is slightly different than the exact centers of the 4-character grid
squares.  This will result in a slightly longer distance for northern
hemisphere to northern hemisphere QSOs and slightly shorter for southern
hemisphere to southern hemisphere QSOs.   The difference for
cross-hemisphere QSOs can go either way, depending on the latitudes of
both stations.

 For example, the distance from the center of my grid square (DM04) to
the center of OH8LAE's grid square (KP44) is 8678.771 km.  The distance
between the center of DM04LL and the center of KP44LL is 8683.097 km, a
more than 4 km greater distance.  The slight error could conceiveably
result in a one-point difference for some QSOs, but Tree says that if
subsquare "LL" is used for all logs that the playing field will be level.

Anyway, if you use DBGRID to score your logs, be sure to use subsquares
"LL" so that your scoring will agree with Tree's.

73 es Season's Greetings, de Earl, K6SE


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