Which statement correctly describes the EIRP calculation formula?

Which statement correctly describes the EIRP calculation formula?

• A. EIRP = Ptx + G + L
• B. EIRP = Ptx - L
• C. EIRP = Ptx + G - L
• D. EIRP = Ptx + L - G

Answer: (C)

EIRP represents the power that would be radiated in a specific direction if the source were an ideal isotropic radiator. To get that value, you start with what the transmitter actually puts out, then account for how the antenna concentrates energy and the losses along the path. The antenna gain increases the power in the direction of interest, so you add the gain. Any losses in cables, connectors, and other components reduce the power that reaches the air, so you subtract the losses. Put together, the correct formula is Ptx plus G minus L. For example, if the transmitter delivers 20 dBm, the antenna gain is 6 dBi, and there are 2 dB of losses, the EIRP would be 20 + 6 − 2 = 24 dBm. Using the other forms would either ignore the gain or improperly treat losses, leading to an incorrect estimate of the radiated power.

EIRP represents the power that would be radiated in a specific direction if the source were an ideal isotropic radiator. To get that value, you start with what the transmitter actually puts out, then account for how the antenna concentrates energy and the losses along the path. The antenna gain increases the power in the direction of interest, so you add the gain. Any losses in cables, connectors, and other components reduce the power that reaches the air, so you subtract the losses. Put together, the correct formula is Ptx plus G minus L.

For example, if the transmitter delivers 20 dBm, the antenna gain is 6 dBi, and there are 2 dB of losses, the EIRP would be 20 + 6 − 2 = 24 dBm. Using the other forms would either ignore the gain or improperly treat losses, leading to an incorrect estimate of the radiated power.