Sign language is just radio communication but on another frequency
Because you use light to communicate in sign language, and light is just an electromagnetic wave like radio but on another frequency. You just need to be in line of sight
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Alas, RADAR relies on transmitting and then reading the reflected waves.
RADAR: RA(dio) D(etection) A(nd) R(anging)
It doesn’t rely on self transmission. It can but you can detect and range other sources without generating it yourself.
That’s just what the acronym means, it doesn’t describes the actual process. I don’t think there is a single RADAR that doesn’t have a transmitter. At that point it would just be a… radio.
Passive radar?
Fair enough, though I would argue that’s a very specific subtype of radar and anyone saying “radar” refers to the type that is used in 99.999% of the cases.
Yeah probably true. I only thought to look it up because I knew active and passive sonar was a thing.