18 Apr 2006 News for NTIA/ITS HF Propagation Models (WINDOWS version) 18 Apr 2006 1. A change was made at a request from a user. He was interested in having the calculations done using an absorption calculation that used to be in IONCAP. It was determined in 1993 that this method produced a value that exceeded the lower limit of an absorption curve. Thus, it was modified to not exceed that value. This limitation was incorporated into VOACAP in June 1999, but I forgot to document it in these news files. A sizeable difference can occur a low frequencies (<3 MHz) at night. Very little data was ever collected at these frequencies when the IONCAP model was developed. It is highly recommended that most users use the "Normal" default absorption model. It will produce a result that is more conserative. For those who are "adventuresome" this option is accessed through the GUI interface by modifying the "SYSTEM" parameters. Once changed, it remains changed for all calculations until changed again. This is only accessible using VOACAP, VOAAREA, ICEPAC, ICEAREA. But will also affect the INVERSE and S/I models. It does not affect any REC533 calculations. This is (internally) accomplished by modifying the VERSION file. Normally the software version reads like: Version 06.0418W If you change the absorption to the old IONCAP model,it becomes: Version 06.0418I This information is output on every type of calculation. Thus, you will know what absorption model was used. If you change the version file by yourself, make sure you know what you are doing. Whenever you download a new version, the "Normal" absorption model will again be implemented. More information about this may come at a later time. Be aware that not everyone involved in the software was in agreement with the change.