This turned up on TheConversation.com which I recently added to my occasionally scanned sources.
https://theconversation.com/device-transmits-radio-waves-with-almost-no-power-without-violating-the-laws-of-physics-196271 This sort of invalidates most of my expectations about what communication channels look like. In this case, the physical transmitter is a tuned antenna connected through a matched resistor to ground with a switch. By toggling the switch on and off it's possible to send 36 bits/second over 7.3 meters. The receiver is essentially hearing the modulation as changes in the noise temperature on the antenna frequency. The PNAS article -- still paywalled -- apparently goes into details of how the receiver works as an electron refrigerator in order to obey the second law, because the reviewers needed to be reassured about that. https://www.pnas.org/doi/10.1073/pnas.2201337119 -- rec --
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