DIY mystery box will wow your friends by hinting at what the ionosphere is up to

A rough guide to when your signal will behave, or not

Shortwave radio enthusiasts are sure to know the problem: You're trying to tune in to your favorite global broadcast only to find that the signal is fuzzy. Is it you? Your equipment? It might just be the conditions in the ionosphere, which you'd know if you built this DIY device. …