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Comment by sciurus | Hacker News Reader

Well, it's 4 days later and we're still here...

I suspect mostly this means some amateur radio operators were annoyed for a few hours.

I suspect the opposite. Solar activity opens paths in bands that otherwise won't DX. So while some or all of HF might close VHF and the lower end of UHF can open and do amazing things.

Aside from amateur radio this would also impact naval and aeronautical radio traffic, both civil and military. Alternatives are usually available (the vulnerability of HF to solar activity is built into the structure of such systems) so it's not a crisis, but it can interfere with people and sometimes a little interference is all it takes to mess things up.

I believe DX in this context means "long distance".

Yeah, more specifically, it usually is referring to radio signal propagating using some form of bounce off the ionosphere. Usually only relatively lower frequencies do this (these are unfortunately named "HF" for high frequency). The more the earth is bombarded by charged particles, the less transparent the ionosphere is to radio signals, so the more likely you are to get a bounce from higher frequencies.

So hilariously true. Personal anecdote: Many years ago, I recall a solar flare hitting during the annual Field Day competition -- I was operating 14MHz phone in the afternoon, great conditions from my mid-west corn-belt location to both East and West coast. Then.... over a period of about 5 minutes it was like a door slammed shut, and there was nothing but noise on the 14MHz band, or any other band. After about a hour or so, I remember the noise level went down from "impossible" to merely "highly obnoxious" and I could barely eek out contacts with stations 50 miles away. 14 MHz is pretty much never NVIS. It took hours for the ionosphere to stabilize again.

Pretty much.

There was no CME associated with this flare, so it didn't cause any geomagnetic effects-- just HF radio interference. If you were trying to listen to your shortwave radio in Australia at the time, you might've been annoyed.

Nothing about this particular event is still impacting us now, although the same sunspot is still active and could produce another large flare or CME at any time. And there's another very active sunspot emerging from the far side of the sun now too.

Aviation uses HF as well, for communications with ATC on oceanic routes.

(Many airplanes on those routes now have satcom as well, though it's not a requirement.)

There could be some impact to GPS as well.

Too high frequency. GPS relies on direct line of sight, and not bouncing signals off the magnetosphere. (This is generally true of all satellite communications)

The ionosphere does weird things to GPS signals as it gets charged up. Delays change based on angle of incidence.

A key part of receiver accuracy is the ionosphere model. If you ignore ionospheric effects your position is likely to only be accurate within about a kilometer.

IIRC these types of solar events can cause some turmoil and even change the size/shape of the atmosphere. That can change how long it takes the GPS signals to get to your phone, which can add noise to the trilateration calculations. Fancier receivers have some clever ways to mitigate that, but your average cell phone GPS chip may lose some accuracy.

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