Propagation white hot

Did you notice the solar flux is at 343? Fifteen and seventeen could stay open into the night.

Elliott, K6EL



Wow, that’s exciting.

While I’ve been licensed since the late 90s, I’ve only really been active since 2015 and those numbers are a first for me.


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The solar flux is super-enhanced because there was a MAJOR Class X2 solar flare today, Feb 17, at about 2015Z. It’s mostly over though (18/0300Z here now).

I was on W0C/FR-064 in the snow doing SOTA when the event occurred. The first thing I noticed was how very quiet the HF bands gradually became. It was as if I had turned off the preamp on my KX2. At about 2000Z I was already aware of the SWF (shortwave fade). I figured it was of little use to proceed on the lower-frequency bands - but I figured that 10 meters would have less fading, and might even be enhanced. At 2005 I started calling CQ on 28.063.

I saw my RBN Hole spot at 28.063 MHz come up on my phone at 2006Z- pretty quick. I contacted four stations in the eastern part of the US, and they were all really strong. That was the end of the activation, as most of the chasers that were on had already got me. I imagine that other SOTA people experienced the effects of this event. I tuned around the bands, and I was stunned by how quiet 40 and 30M were - almost no noise was available to peak my tuner! Only a few signals were audible on 20M CW, but a couple were loud. The high solar flux during a flare will cause increased absorption in the D layer, which makes lower frequencies fade severly, but it also causes increased ionization in the F layer, which can support unusual high-angle propagation at higher frequencies.

I heard odd varying noise on 10M, not man-made. I’m pretty sure these were solar radio bursts during the peak of the flare. I was on a quiet summit, so this is to be expected.

A curve of the flare’s x-ray enhancement and other info are available at the NOAA site here:

Please look at the graph for the GOES X-RAY FLUX.

Images of the flare, and more info are here:

Now that we’re having a “hot” solar cycle, these websites are worth watching.

Remember that the 10 cm solar flux is an indirect measurement of the sun’s activity. The X-ray flux is the real deal - that’s what modifies our ionosphere and lets us work DX. A major solar flare can increase the x-ray output of the sun by over 1000 times at maximum. Note that the NOAA data is on a logarithmic scale.

This was the strongest solar flare I’ve ever noticed while on the air. There will be many more - and they can change what you do on your summits!





Yes, however the Kp Index is heading for SIX today (G2 storm) - I expect RF Blackouts somewhere in the world.

So grab any good conditions when they are there but expect lots of atmospheric noise on the lower bands.
73 Ed.


Pointing the 6m beam to VK just in case there is propagation!

73 Phil



Hi Mark,
that 343 reading from Colorado (also displayed at is from 8 am this morning and hasn’t changed, which makes me suspect it might be a false reading.

Bremen, Germany at 1300 UTC reported a peek SFI of 245 (based on data from Canada)- so still VERY GOOD but with the Kp Index expected to hit SIX today, the conditions could be VERY changeable.

The band activity graph from DXHeat is not particularly special (that’s based on DX Cluster spots I believe). So it’s saying to me that inter-Europe should be good but further afield may not be as good as you would expect from such a high SFI value.

73 Ed.

More research - the 343 value appears to have been a spike last night - it was already back at 180 by 2200 here are 3 values out of Canada:

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Fowarding this on from the CDXC Reflector:

" From: W3UR Bernie McClenny
Date: Sat, 18 Feb 2023 12:15:27 GMT

Every day, at the exact specific time, the SFI is measured. Yesterday when the measurement was taken we got the extremely high (invalid) SFI while the solar flair took place.

Bernie McClenny, W3UR

Editor of: The Daily DX (1997-2022)
The Weekly DX (2001-2022)
How’s DX? (1999-2022)"


Hi Geo,
I am curious about the fact that you noticed an almost immediate effect right after this event, if I understand you correctly.

Perhaps I am wrong but I would expect any noticeable effect on the propagation some hours after the event happened in the sun?

73 Ignacio

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There was a radio burst which travels at the speed of light. The eruption has also hurled a cloud of charged particles towards us which are due to arrive this weekend.


This is a Type II solar radio burst. Shock waves from the flare rippled through the sun’s atmosphere, creating plasma oscillations that emit shortwave energy. Briefly, the sun turned itself into a natural radio transmitter.

I was up at 4am (jet lagged and still really on UK time) and checked 15m and 10m. Zippo.

However not to miss a chance I headed up to w6/sc-369 around 8am local time and 15m was OK but 10m had a great opening into the EU and UK. Some stations (presumably running QRO) were ridiculously strong. My 75w into a dipole did the job and I was happy to net contacts across the EU and UK.

Thanks to @SA4BLM, @F4WBN, @EA2DT, @G4IPB, @GI0AZB and @GI0AZA to name a few.

In stark contrast to me activation with Andy, north of Perth 2 weeks ago, its balmy sunshine and warm (hot).


I was listening on the higher bands today but didn’t notice anything special.

There was a lot of CW activity but I think that will be the ARRL DX CW contest this weekend.

Hi Paul,
It’s good that operators are now getting occasional, delicious tastes of what propagation was like about 1957. I’m sure Elliott, K6ILM (now K6EL) remembers!

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I saw your spot and listened on 15m but didn’t hear you, would have been nice to get a S2S but I only had 5w :slight_smile: Only 4 contacts for me on 15m this afternoon.

Thanks Paul (W6PNG) for the contact - I have a relatively modest set up at home but the vertical with 100w worked so I’ve managed both VK and W6 this week (SSB) . ( I do have a low noise floor now the power line issues have been fixed…) … Just waiting for that DX S2S which seems to require an unusual combination of events - tolerable weather, good band conditions and not being needed for anything else! 73. Paul


Well I had a nice relaxed chat with a VE this afternoon on 10 m SSB, just running 10 w into my EFHW. No fading, 5 & 7 both ways. 40 was painful. 15 sounded dead, but was alive and 20 was behaving like 40!


I’m not sure if it is related to the Solar conditions but today I managed a QSO from GM/SS-125 Scald Law to a ZL4 in Dunedin on 15m. He was 58 into me but I was 44 at his end, not bad for 5 watts into a link dipole, but I think his antenna was doing a lot of the work.
I managed to work an S2S to Wales on 40m but couldn’t hear any of the European SOTA stations that were spotted on that band.


Well done! That’s fantastic.

It certainly is. Wouldn’t have happened 12 months ago.

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Solar x-rays affect our ionosphere almost immediately after they reach earth. So the short wave effect is very fast, as soon as we see the flare from earth, in other wavelengths.

Other solar effects, such as charged particles ejected by flares, often take hours to days to reach earth.

Solar radio bursts occur during and after the x-ray peak of the flare, and they appear as noise on our radios.

Since the Class X2 flare that caused the recent fade was on the east side of the sun, we don’t expect to see many effects from particles.



That was most likely Ron ZL4RMF? He puts a great signal into Europe when the higher bands are open and even through the last few years, he was there on 40 & 80m via Greyline. A really nice Gentleman and a pleasure to work.

73 Ed.

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