> Modern modulation techniques are insanely efficient. It's amazing that mobile phones work. There's old modulation techniques that are crazy efficient too - t

> Modern modulation techniques are insanely efficient. It's amazing that mobile phones work. There's old modulation techniques that are crazy efficient too - the most obvious one being GPS. A small antenna, just 2cm short [1], is all you need to pick up and distinguish from each other the signal of up to a dozen different GPS and dozens of other (GLONASS, Galileo, BeiDou) navigation satellites. This is mind-blowingly nuts. For modern high-bandwidth communication, microwave point-to-point links can achieve 65km range with barely 4 watts of RF energy - e.g. German Telekom's Skylink system connecting an aviation radio transmitter on the island of Helgoland with the continental backbone at Cuxhaven [2]. And actually that is way more power than required, half a watt is enough but they chose to go for higher power to achieve perfect reliability even in worst-case conditions [3] (does make sense, given how safety-critical flight radio communication is). If all you need is satellite communication for a few bytes of information, a cellphone can send an emergency message to satellites anywhere on this planet (at least, where regulatory clearances allow for that) [4]. [1] https://electronics.stackexchange.com/questions/586900/how-can-a-9mm-square-antenna-pick-up-gps https://electronics.stackexchange.com/questions/586900/how-c... [2] https://www.youtube.com/watch?v=q_Ja6QtWwpQ https://www.youtube.com/watch?v=q_Ja6QtWwpQ [3] https://www.telekom.com/de/blog/netz/artikel/skylink-richtfunkstrecke-auf-helgoland-612072 https://www.telekom.com/de/blog/netz/artikel/skylink-richtfu... [4] https://support.apple.com/de-de/101573 https://support.apple.com/de-de/101573