Grayline version 1.2, by PA3CQR
===============================

Main purpose of the program.
----------------------------

The main purpose of the program is to help radioamateurs and shortwave listeners
to benefit from so called 'grayline propagation'. A short explanation :
The grayline is a virtual line which divides the earth in the day and the night side. 
When 1 radiostation is in the dusk and the opposite station is in the dawn, there is a
possibility for so called 'grayline propagation'. At sunrise the D-layer builds up slowly
and at sunset it disappears slowly again. During this change, low frequencies are not
absorbed but refracted by the D-layer and they will enter the F-layer with a much lower
wave angle than normal. In this way longer distances can be used for propagation on
the lower hf bands. Grayline propagation occurs in general from about 1.8 to 10 MHz
and the propagation paths will be in the dark.

The program calculates possible grayline propagation paths for your location to other
DXCC countries for any given date.
The sunrise/sunset calculation algorithm is taken from 'Van Heddeghem', ON4HW and can be
found in the book 'Low-Band DXing' by John Devoldere ON4UN published by the
A.R.R.L. ( First edition Second printing page I-17 ). The grayline width calculation
algorithm is from John Devoldere, ON4UN published in the same book at page
I-6 and I-7.

System requirements:
--------------------
An IBM compatible PC with MS-DOS 5.0 or higher and 128 kB free RAM.
A mathematical coprocessor is not needed but will speed up the program.
The program will also run in a MS-DOS window within MS-Windows 3.11/95/98.

Installation.
-------------

All the files in the zip archive must be placed together in a subdirectory which
can have any name you like.
Next the grayline.ini file must be edited with an ascii editor. 
The first line is your latitude in decimal degrees (north uses +, south uses -).
The second line is your longitude in decimal degrees (west uses +, east uses -).
The third line is the time offset (hours) compared to UTC. Enter a zero if you want
to display UTC times. Corrections for Daylight Savings Time must be made manually !

Now you can run grayline.exe from the MS-DOS prompt or double-click the grayline.exe file 
from Windows explorer.

The program is easy to use. It asks for what day you want grayline path
calculations and if you would like the results on your screen or written in
a text file. On the screen you can scroll through the results with the arrow
keys and switch between the predicted paths for sunrise and sunset with the
'PageUp' and 'PageDown' keys. Use the 'End' key to leave the program.
If you choose to write to a file, the data is written in an a textfile called grayline.out

Adding / removing DXCC entries.
-------------------------------

The grayline.dat file is a comma delimited DXCC country list which can be
modified if there will be new dxcc entries or if entries will be removed.

The format is : prefix,city,country,latitude,longitude,cq-zone

    prefix    : max.  5 positions
    city      : max. 19 positions
    country   : max. 19 positions
    latitude  : decimal degrees (north uses +, south uses -)
    longitude : decimal degrees (west uses +, east uses -)
    cq-zone   : 2 digit integer between 01 and 40

Status / Distribution status of the program.
--------------------------------------------

This program is freeware. The zip archive can be freely distributed as long as the contents
of the archive and the contents of the files in the archive are NOT changed.

Credits to John Devoldere ON4UN and Van Heddeghem ON4HW.
Special thanks to Cesar PY2YP who carefully checked and debugged the DXCC datafile.
Any critics for improvement are welcome.

73, Folkert PA3CQR

How to contact the author.
--------------------------

You can contact the author by e-mail at geurink@iri.tudelft.nl
More info at url http://www.iri.tudelft.nl/~geurink/grayline.htm

