It's probably not super "significant", but it's neat. Someone has a light bulb (the omni-directional beacon) 40 km away, and completely invisible if you go look

It's probably not super "significant", but it's neat. Someone has a light bulb (the omni-directional beacon) 40 km away, and completely invisible if you go looking for it (from his ground station location). The author pointed a telescope (his directional ground station antenna) straight up and on a rainy day and could see the light bulb turn on and off.