A radar needs an echo strong enough to return from the target to the transmitting ship. An enemy receiver detecting the outgoing signal does not depend on that return journey. The range comparison places detection of the radar's emissions at twice its target-detection range. This creates a tradeoff between obtaining warning and advertising the radar's presence. Visual observation does not reveal the observer through a comparable transmitted signal.
Notable Point · 20:29-21:16
Radar detection also reveals the transmitter
Radar gives a fleet warning of an attack, but its transmitted signal can also reveal the radar to a receiver farther away.