Antennas
Effective Radiated Power
- Radiated power is power supplied at the antenna system multiplied by the antenna gain
in a given direction. This can be referenced to a half-wave dipole
(Effective Radiated Power ERP) or an isotropic radiator
(Effective Isotropic Radiated power EIRP)
- For a transmitting system it is determined by subtracting system losses from system gains
- For example if an antenna system has a 6dBd gain and a feeder loss of 3dB
then the system (antenna and feeder) has an effective gain of 3dBd (a power gain of two)
- If the transmitter outputs 100 watts, the system will have a ERP of 200 watts;
a Tx power level of 20 dBW becomes ERP of 23 dBW
- Recall: Gain in db. If the ratio power out / power in is less than 1,
then a loss is involved and the dB figure will be negative