26 Mar  2009    News for NTIA/ITS HF Propagation Models (WINDOWS version)

26 Mar  2009   1. A change was made to VOACAP and ICEPAC in the MPROB parameter.
                  MPROB is not the probability that multipath exists.
                  It is rather the reliability of the next most reliable mode
                  that lies within the multipath parameters on the SYSTEM card.
                  When there are multiple modes avaliable, both VOACAP & ICEPAC
                  calculate the Most Reliable Mode (MRM). This may not be
                  the mode with the highest reliability or highest signal power.
                  If two modes are close in reliability, a mode with fewer
                  hops may be selected as the MRM. Thus, a 2F2 mode might be 
                  selected over a 3F2 mode.
                  On the SYSTEM card, there are 2 parameters that are used to
                  determine if multipath might exist.
                  Multipath Power Tolerance (dB) is the maximum difference in
                     signal power between modes to determine if multipath exists.
                     Modes with signal power greater than this value below the 
                     MRM are examined. Previously, modes with higher signal
                     power than the MRM could have been ignored because only
                     modes within +/- this value were examined.
                  Maximum tolerable time delay (milliseconds) is a value such that
                     modes within this time delay of the MRM are not considered
                     to cause multipath problems.

                  Additionally, MPROB is only calculated using the "short path"
                  model.  Thus, if you use METHOD=30 (the suggested method),
                  MPROB is only valid for distances less than 7000km.
                  This is because METHOD=30 uses the short path model for
                  distances <7000km and the long path model for distances >10000km.
                  It interpolates between the two models in the 7000km to 10000km.
                  If you use METHOD=20, MPROB is calculated for distances <10000km.
                  If you use METHOD=22 (forced short path), MPROB is calculated
                  for all distances.
                  If you use METHOD=21 Iforced long path), MPROB is not calculated.

                  This change does not affect any other parameter.
                  Most users do not use MPROB as it does not tell you if
                  multipath exists. That information is beyond the scope of
                  these models and is reserved to The Almighty Spirit (as
                  mentioned by Klaatu in The Day The Earth Stood Still).
                  Sorry about that, but the original was such a good movie.