For example, consider a 10 W transmitter at a distance of 1 million metres, radiating over a bandwidth of 1 MHz. By the time that power has reached the observer, the power is spread over the surface of a sphere with area 4 πr or about 1.26×10 m, so its flux density is 10 / 10 / (1.26×10) W m Hz = 8×10 Jy.