so ive been trying to work some DX on 20m and 17m the past few weeks and its been really hit or miss. like some days i hear almost nothing from Europe and then randomly thursday evening i worked 4 stations in the UK and a guy in Portugal back to back no problem. then the next day absolute silence again.

i checked pskreporter and there were signals getting through so its not my antenna (probably). i know solar flux has been kinda all over the place but i dont really have a good feel for how to read the numbers and actually predict when a band is gonna open up. like what SFI number should i even be looking for before i bother trying for transatlantic stuff? and does the K index actually matter as much as people say or is that more for VHF aurora stuff

sorry if this is a dumb question, been licensed about 8 months and still figuring out when to even bother turning the rig on

not a dumb question at all, this stuff trips up people who've been at it for years honestly. the short version is that SFI (solar flux index) above 120 or so is when 20m really starts to come alive for transatlantic, though you can still get good openings in the 100-110 range especially during the gray line periods — that's sunrise and sunset when the ionosphere does interesting things. below 100 it gets spotty and patience becomes your main tool.

the K index is kind of a separate thing — that's geomagnetic activity and yeah high K (above 4 or 5) will wreck HF propagation, especially the higher bands, not just VHF. so ideally you want high SFI AND low K. there are days where the flux looks great but K shoots up from a CME and it all goes sideways. i use the DXheat bandscope and also just check the NOAA space weather site when i'm feeling nerdy about it.

the random thursday you described sounds like a classic evening gray line opening — those can be spectacular and then totally gone the next day. that's not you doing anything wrong, that's just how it works

yeah what he said about the greyline is spot on. i'd also add that wwv broadcasts propagation conditions at 18 minutes past every hour if you tune to 10 or 15 mhz — old school but i still do it sometimes just to hear a voice tell me the numbers lol. also the DX cluster on 14.225 area tends to get busy when europe is actually in so that's kind of a lazy way to know if a band is open without spending an hour calling CQ into the void