The term effective isotropic radiated power (EIRP) is derived from the word isotropic which means equal in all directions. Effective isotropic radiated power means the power levels that would be received at any location if an antenna were radiating equally in all directions. Therefore, a 37 dBw EIRP reading means that a perfect antenna would direct 37 dBw or 5012 watts per square meter in all directions. The reason that a transponder having rather limited power, typically in the 8 to 150 watts range, can apparently have such a high EIRP stems from the fact that this power is not radiated equally in all directions but is concentrated in a narrow beam aimed at the earth below. Ku-band transponders having a total power of 50 watts have EIRPs as high as 48 or 49 dBw when this power is directed into a tightly aimed zone beam.RP levels refer to the power of signals measured at the satellite downlink antenna. In the example above, 5012 watts per square meter would be directed towards a selected location on earth below.