Documentation on how IPS creates real time NAP charts and there use can be found in the document: IPS NAP Chart Construction (PDF File) The Best Usable Frequency (BUF) NAP is a new product that includes customer antenna type (propagation angle), required percentage of days and signal to noise ratio into the prediction. The BUF NAP shows the strongest predicted frequency compared to the real time Maximum Usable Frequency (MUF) NAPs showing the highest supported frequency. There can also be differences between the two products particularly around dawn and dusk, when the ionosphere is changing rapidly, as the BUF and MUF NAP charts are currently generated at different times within the hour.
Real time NAP charts are limited in area to the IPS real time Australia/NZ foF2 map area of
coverage. Perth IN01 and Port Hedland INO1 HAP charts (which the Perth-PortHedland NAP is based)
extend outside this range (to 70 degrees East). The 70 degrees east charts are based on the IPS World foF2
map which updates an hour behind, the Australia/NZ map. For this reason there are two NAP charts for the
Perth Port Hedland INO1 NAPs, one using the Australian real time map, the other the world real time map.
The Darwin site can sometimes be affected by interference so alternative NAPs are available for domestic HF communications
without the Darwin site.
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