Normal HF communication works when there's a "window" between the lowest usable frequency and the maximum usable frequency. Solar flares can cause the maximum usable frequency to be below the lowest usable frequency, a condition of HF blackout.

Does that mean that it's game over for communication? We look at what happened on August 28, 2020 on the BLACK SWAN Net as an example of how to put some key concepts like an operating schedule, a PACE Plan, and standard systems of relay together to make communication work, even if it isn't as expected.

CONTENTS
00:00 Introduction
00:32 What is Radio Blackout?
01:07 Alert! (Blah blah blah)
01:20 Fundamental HF Radio Concepts
03:19 NVIS Short and Medium Distance
03:44 Making Send of the Alert
04:17 SWPC Imagery Illustrates Absorption
06:48 Calling Net Per Plan
07:08 Finding Usable Frequency With WWV and CHU
09:04 Finding Net Stations On-Air
09:44 Using Relays (Automated or Manual)
11:23 Working Through Adverse Conditions

REFERENCES
NOAA SWPC Radio Communications Dashboard https://www.swpc.noaa.gov/communities...