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Hi all,
For example we have Transmiter+combiner+spliter+feeder+antena.After losses computation we have +17dBm at the input of antenna. Antenna have 2 dBi gain. How to compute radiated output power from antenna ? How many dBm can i expect, input power is +17 dBm ?
17dBm + 2dBi = 19 dBm
your EIRP (radiated power) = 19 dBmit’s as simple as that 🙂
I assume it is an omni directional antenna ? in this case, in all 360 degrees, there will be a TX power of 19 dBm.
In case of panel antennas, only in the main direction of the lobe will you have 19 dBm. In other directions, you must include a certain attenuation (check the antenna pattern).
Regards
pixYes ant is omni for example, but i don’t understand how can be used addition or substraction on two different quantities
decibels are a weird unit 🙂 but very convenient !
dBm are absolute power, they correspond to a certain amount of mW. For instance 0dBm = 1mW, 33dBm = 2W.
dBi are relative power: they indicate how much gain is given to an input signal. It’s like the “dB”.
For instance :
0dBm + 3dB = 3dBm = 2mW
3dBm + 3dB = 6dBm = 4mW
6dBm + 3dB = 9dBm = 8mW
9dBm + 3dB = 12dBm = 16mWAs you see, 3dB is not equal to xx dBm. It is a factor which means the power (in watts) is multiplied by 2.
An antenna “multiplies” the input power by a certain factor. It’s “relative power”.
Wow, it’s clear now 🙂 🙂
Thank you very much for detailed and usefull explanation !
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