HF Fadeout Warning

(last updated 04 Sep 2025 19:25 UT)

SUBJ: ASWFC HF RADIO COMMUNICATIONS WARNING 25/82 ISSUED AT 0123UT/03 SEPTEMBER 2025 BY THE AUSTRALIAN SPACE WEATHER FORECASTING CENTRE. There are currently 10 numbered sunspot regions on the visible solar disk. Shortwave fadeouts are possible. DEGRADED HF PROPAGATION CONDITIONS EXPECTED FROM 03-05 SEPTEMBER 2025 IF COMMS DIFFICULTIES EXPERIENCED TRY A HIGHER FREQUENCY BAND _____________________________________________________________ SOLAR ACTIVITY FORECAST HF COMMS FADEOUTS 03 Sep: R1 Possible 04 Sep: R1 Possible 05 Sep: R1 Possible Note: An ASWFC MUF depression HF Warning and ASWFC shortwave fadeout HF Warning are both current. Shortwave fadeouts degrade lower shortwave radio frequencies first (through increased ionospheric absorption) and the usual strategy during shortwave fadeouts is to try a higher frequency. In contrast, during periods of ionospheric MUF depression, the upper frequencies are degraded first and the usual strategy is to use a lower frequency. In general use a lower frequency if you are having trouble with your normal workable frequency. If a shortwave fadeout occurs during a period when ionospheric MUFs are depressed the available HF bandwidth will be "squeezed", with increased absorption raising the lowest usable frequency and the ionospheric depression lowering the highest usable frequency. Under such conditions it is suggested that the HF communicator operates on the highest usable frequency, even though this may well be in fact lower than what is normally supported for that particular circuit.