Instructions for Patching YT.EXE                   Sep 08, 1997

This patch removes a very subtle bug in YT.EXE Version 1.0, and 
makes Version 1.1. Thanks to K4AB for pointing the problem out. 
The bug shows up only in certain complex terrains, where 
diffraction points may not be visible from different Yagis in a 
stack and where the operator has specified antenna heights in an 
"upside down" fashion. 

For example, if your stack has Yagis at 90 and 50 feet, it's 
possible that the 50-foot-high Yagi can't "see" certain 
diffraction points because they are shadowed by your particular 
terrain, while the higher Yagi at 90 feet can see the diffraction 
point directly. If you specify the heights as #1 = 90 and #2 = 50 
feet (that is, the "normal" method -- meaning that's the way I do 
it!), everything is OK. But if you specify them as #1 = 50 and #2 
= 90 feet, the bug may show up. You can overlay the two scenarios 
together to see if the two computations line up exactly, as they 
should.

                DIRECTIONS FOR USING PATCH-YT.EXE

Copy these two files to the subdirectory containing the original 
YT.EXE installed from the diskette bundled with the 18th Edition 
of The ARRL Antenna Book (probably the C:\ANTBOOK\TERRAIN 
subdirectory if you followed the defaults at installation):

PATCH-YT.EXE
YT.PAT

Then, type:

PATCH-YT [Enter]

and the program will automatically patch your copy of YT.EXE. It 
will terminate if it doesn't find either an original YT.EXE or 
the file YT.PAT, the patching file.



73,

Dean Straw, N6BV
Senior Assistant Technical Editor, ARRL
n6bv@arrl.org
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