Topband: greyline forecast for 80m

[S57AD]

W6EL prop program helped me to work my first (and single, so far) Alaska on
80m some 20 years ago.


73, Mirko, S57AD

2017-02-17 18:50 GMT+01:00 Merv Schweigert via Topband <
topband at contesting.com>:

> I agree seat time is the only sure way.  I have tried a number of
> different prop programs
> and have not been satisfied so to speak.
>
> What I use now most of the time does not specifically show grey line, but
> does do long
> and short path,  and you can "estimate" grey line by the sunrise / sunset
> times shown
> and the path predictions to the destination.
>
> It is the old old W6EL prop program.
>
> For me it has been very accurate in predicting openings,  simple to use.
> Have been able to snag needed countries on the low bands using this tool,
> its interesting
> to be sitting on the freq and hearing just whispers of the DX, and as the
> time plotted
> by W6EL approaches the signal comes up out of the noise and you have a
> shot at
> working them.
> Some times the window is very short,  but it seems to be pretty accurate
> as to time / freq.
> It only covers 80 to 10 meters by the way.
>
> 73 Merv K9FD/KH6
>
> Hello Kris N5KM,
>>
>> Thanks for the clarification.
>>
>> 80m is a different story. Yes, we can predict greyline propagation on 80m
>> (I assume when you say greyline propagation, you mean propagation along
>> the
>> terminator). And our predictions say there is still significant loss along
>> and near the terminator on the low bands. Simply put, absorption is
>> proportional to the product of electron density times electron-neutral
>> collision frequency - so as we progress from day to night, absorption
>> moves
>> up from the D region to the lower E region. There is still a prohibitive
>> amount of absorption along the terminator on the low bands.
>>
>> What I and others believe is that what really happens is the RF takes a
>> short cut across the dark ionosphere, where absorption is minimal. The RF
>> gets far enough away from the terminator to minimize absorption, but not
>> far enough away to look like it's not greyline. Thus the importance of the
>> greyline is to put both ends of the path in or near darkness. For a great
>> article on 80m greyline, read Ed N4II's article in the Nov/Dec QEX titled
>> "Gray Line Propagation, or Florida to Cocos (Keeling) on 80m". I have
>> written about the problems with "greyline propagation" numerous times, but
>> N4II's article is more elegant!
>>
>> So can we predict this alternate explanation of greyline? Unfortunately,
>> no
>> - as it involves two great circle paths joined by a skew point. Having
>> said
>> that, many years ago Rod VE7VV developed a DOS program to address these
>> skewed paths. I am not familiar enough with it at the moment to offer any
>> comments. I believe Bill W4ZV has used it more extensively. One comment -
>> the output of this program appears to be in terms of a monthly median,
>> since the model of the ionosphere in our prediction programs is a monthly
>> median model. In other words, VE7VV's predictions say something like a
>> signal will be so many dB above 0.5 uV on a percentage of days.
>> Unfortunately, we do not know which will be the good days. Bottom line -
>> keep you butt in the chair at the appropriate times.
>>
>> Carl K9LA
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-- 
Mirko S57AD