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 _________________ Topband Reflector Archives - http://www.contesting.com/_topband
