Question
What term describing total radiated power takes into account all gains and losses?
Answer Options
- A) Power factor
- B) Half-power bandwidth
- C) Effective radiated power
- D) Apparent power
Correct Answer: C
Explanation
In a radio system, the power coming out of the transmitter is rarely the same as the power actually leaving the antenna. Components like feed lines, connectors, and filters introduce losses that reduce the power, while the antenna’s directivity introduces gain that increases power in specific directions.
The term that describes the maximum total radiated power after taking into account all gains and losses in the system (transmitter output, line losses, filter losses, and antenna gain) is Effective Radiated Power (ERP). ERP is the figure used to determine the legal power limits and for calculating signal strength over a path. It is the power, in Watts, that would have to be radiated by a dipole to give the same maximum radiated signal power in the strongest direction, given the antenna actually in use. (The difference in maximum radiated power between a particular antenna and a dipole is expressed in dBd, decibels relative to a dipole.)
(By contrast, Effective Isotropic Radiated Power, EIRP, is a theoretical figure that imagines an antenna that radiates power equally in all directions. Power expressed in ERP will be exactly 2.15dB lower than EIRP. EIRP is used in some other jurisdictions; US regulations use ERP. The difference in maximum radiated power between a particular antenna an an imaginary isotropic radiator is expressed in dBi, decibels relative to an isotropic radiator.)
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