Задача id14082

A signal from a radio transmitter received at a distance l0 = 1 km is equal in power to the level of the receiver’s own thermal noise. From what distance l can reception be carried out with the same signal-to-noise ratio if the input circuits of the receiver are cooled from room temperature T0 = 300 K to liquid helium temperature T = 4.2 K?

Answer. Format gif