Hourly NAP Charts
Documentation on how SWS creates real time NAP charts and their use is available: SWS NAP Chart Construction (or PDF). 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 SWS 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 SWS World foF2 map. For this reason there are two NAP charts for the Perth Port Hedland INO1 NAPs, one using the Australian real time foF2 map, the other the world real time foF2 map.
The Darwin site can sometimes be affected by interference so alternative NAPs are available for domestic HF communications without the Darwin site.